Organometal halide perovskite solar cells (PSCs) are nowadays regarded as a rising star in photovoltaics. In particular, PSCs incorporating oriented TiO2 nanorod (NR) arrays as the electron transport layer (ETL) have attracted significant attention owing to TiO2 NR's superior electron transport abilities and its potential in long-term stable PSCs. In addition to improve the electron-transport ability of TiO2 NRs, the tuning of the band alignments between the TiO2 NR array and the perovskite layer is also crucial for achieving efficient solar cells. This work describes a facile, one-step, solvothermal method for the preparation of tantalum (Ta) doped TiO2 NR arrays for efficient PSCs. It is shown that the trace doping with Ta tunes the electronic structure of TiO2 NRs by a synergistic effect involving the lower 5d orbitals of the doped Ta5+ ions and the reduced oxygen vacancies. The synergistic tuning of the electronic structure improves the band alignment at the TiO2 NR/perovskite interface and boosts the short-circuit current and the fill factor. By using the optimized doped TiO2 NR array as the ETL, a record efficiency of 19.11% was achieved, which is the highest among one-dimensional-array based PSCs.

Organometallic halide perovskites have expanded promising approaches for fabricating optoelectronic devices with low cost and high performance since their discovery. Here we propose a novel technique, flash evaporation printing, to prepare perovskite thin films with high quality in an efficient way, whose success is attributed to freestanding carbon nanotube films serving as the flash evaporator. It is convenient to print patterned perovskites using this method due to the compact deposition geometry. The patterned perovskite thin films were further manufactured to planar-type photodetectors, and the performance of the photoelectric devices was evaluated. The as-prepared photodetector shows a considerable peak responsivity and fast temporal response, proving flash evaporation printing an effective route for exploiting high-performance perovskite photodetectors, and this technique can find potential applications in more fields.

Vertically aligned ZnO/ZnTe core/shell heterostructures on an Al-doped ZnO substrate are developed for non-toxic semiconductor sensitized solar cells. Structural and morphological analysis serves as evidence of the successful synthesis of ZnO nanorods, ZnTe nanocrystals and ZnO/ZnTe heterostructures. The clearly observed quenching of photoluminescence (PL) from the heterostructure indicates efficient charge transfer occurring at the interface of ZnO and ZnTe, due to the type-II energy level alignment constructed by the two. The formation mechanism of the ZnO/ZnTe heterostructure is studied in depth via time-dependent reactions. It was found that the strain between ZnO and ZnTe modifies the band alignment at the interface of the heterostructure in a manner which depends on the growth time. Finally, sensitized solar cells based on the ZnO/ZnTe heterostructures with different ZnTe growth times were fabricated to evaluate the photovoltaic performance. By the careful control of the ZnTe growth time and as a result of the band alignment between ZnO and ZnTe, the power conversion efficiency (PCE) of the vertically aligned ZnO/ZnTe based solar cells could be improved to about 2%, along with a short-circuit photocurrent density of around 7.5 mA cm−2, a record efficiency for ZnO/ZnTe based sensitized solar cells. Notably, for the optimized system the internal quantum efficiency of the ZnO/ZnTe based solar cell approaches 100% in certain wavelengths, implying effective separation of photoexcited free carriers towards either the electrolyte or anode.

•Anthocyanin and Chlorophyll extracted from Trollflower and Cypress leaf respectively are used as natural sensitizers.•Optical properties and stability of anthocyanin and chlorophyll are individually investigated.•Anthocyanin and Chlorophyll are purified with High Performance Liquid Chromatography.•Anthocyanin: chlorophyll (2:5) renders both an optimized electron injection and regeneration driving force of dye molecules.Anthocyanin and Chlorophyll extracted from Troll flower and Cypress leaf respectively are used as natural sensitizers in dye sensitized solar cells (DSCs), with their optical and electrochemical properties investigated. UV–Vis absorption measurement showed that the mixture of two dyes enabled an enhanced and wider absorption in the wavelength range of 300 nm–700 nm compared to each single dye. FTIR results proved that anthocyanin is chemically adsorbed onto the TiO2 film, while it is physical adsorption for chlorophyll. The energy level offsets on the TiO2/dye/electrolyte interface for each dye and the dye mixture with different ratios were calculated from the electrochemical analysis, which affect the electron injection and dye regeneration efficiencies. The optimized ratio of the two dyes in the mixture was found to be ∼2:5, inducing both sufficient charge transfer driving force and minimal energy loss. By incorporating this mixture into the solar cell as co-adsorbing sensitizer, the photovoltaic performance was prominently improved compared with the single dye sensitization system.

ZnTe, a non-toxic low band gap semiconductor, has a direct band gap of 2.26 eV, and can be a promising candidate for non-toxic semiconductor sensitized solar cells (SSSCs). Herein, we report a simple and low-cost solution-processing approach to synthesize ZnTe nanocrystals by using dendrite-like ZnO nanorods as templates via an in situ method for application in solar cells. Structural and morphological analyses and systematic optical property investigations evidenced the successful synthesis of ZnTe nanocrystals and ZnO/ZnTe heterostructures. The measured band alignment of the heterostructures directly points to the strong effect of strain and the possibility to engineer the band offset at the ZnO/ZnTe interface. As ZnO and ZnTe exhibit a type-II energy level alignment, both significant absorption and efficient charge transfer are enabled between the two. Finally, solar cells based on the ZnO/ZnTe heterostructure were fabricated and a short-circuit photocurrent density of over 5 mA cm−2 was achieved, benefiting from the preeminent absorption, high charge separation and transfer efficiency. A ZnS passivation layer dramatically improved the performance of the solar cells reaching a short-circuit photocurrent density of over 10 mA cm−2, along with an increase in the power conversion efficiency (PCE) from 0.46% to 1.7%. Potential pathways towards further increasing this figure are discussed.

Although low-temperature, solution-processed zinc oxide (ZnO) has been widely adopted as the electron collection layer (ECL) in perovskite solar cells (PSCs) because of its simple synthesis and excellent electrical properties such as high charge mobility, the thermal stability of the perovskite films deposited atop ZnO layer remains as a major issue. Herein, we addressed this problem by employing aluminum-doped zinc oxide (AZO) as the ECL and obtained extraordinarily thermally stable perovskite layers. The improvement of the thermal stability was ascribed to diminish of the Lewis acid–base chemical reaction between perovskite and ECL. Notably, the outstanding transmittance and conductivity also render AZO layer as an ideal candidate for transparent conductive electrodes, which enables a simplified cell structure featuring glass/AZO/perovskite/Spiro-OMeTAD/Au. Optimization of the perovskite layer leads to an excellent and repeatable photovoltaic performance, with the champion cell exhibiting an open-circuit voltage (Voc) of 0.94 V, a short-circuit current (Jsc) of 20.2 mA cm–2, a fill factor (FF) of 0.67, and an overall power conversion efficiency (PCE) of 12.6% under standard 1 sun illumination. It was also revealed by steady-state and time-resolved photoluminescence that the AZO/perovskite interface resulted in less quenching than that between perovskite and hole transport material.Keywords: aluminum doping; perovskite; solar cell; thermally stable; zinc oxide

We report herein perovskite solar cells using solution-processed silver nanowires (AgNWs) as transparent top electrode with markedly enhanced device performance, as well as stability by evaporating an ultrathin transparent Au (UTA) layer beneath the spin-coated AgNWs forming a composite transparent metallic electrode. The interlayer serves as a physical separation sandwiched in between the perovskite/hole transporting material (HTM) active layer and the halide-reactive AgNWs top-electrode to prevent undesired electrode degradation and simultaneously functions to significantly promote ohmic contact. The as-fabricated semitransparent PSCs feature a Voc of 0.96 V, a Jsc of 20.47 mA cm–2, with an overall PCE of over 11% when measured with front illumination and a Voc of 0.92 V, a Jsc of 14.29 mA cm–2, and an overall PCE of 7.53% with back illumination, corresponding to approximately 70% of the value under normal illumination conditions. The devices also demonstrate exceptional fabrication repeatability and air stability.Keywords: composite metallic; perovskite solar cells; semitransparent; silver nanowires; top electrode

A panchromatic hybrid photoelectrode featuring co-sensitization of PbS quantum dots (QDs) and dye N719 with high charge separation efficiency was designed. In this photoelectrode, PbS QDs and N719 dye molecules exhibit a type-II energy level alignment, enabling efficient charge transfer between the two sensitizers and enhanced charge injection efficiency from sensitizers into TiO2, as confirmed by the significant PL quenching and time-resolved photoluminescence. Furthermore, we show the utility of a cobalt(II/III)-based redox electrolyte in solar cells based on PbS–N719 co-sensitized photoelectrodes, achieving a photovoltaic efficiency of over 2%. This result is comparable to the highest efficiencies obtained in cells of this type, and further verifies the important role of N719 as an intermediary agent in hole extraction from the PbS QDs. Compared to QD-only sensitized cells, co-sensitization significantly enhances the cell performance: the overall energy conversion efficiency by about 40% (from 1.55% to 2.12%) and the fill factor by about 20% (from 0.50 to 0.59). However, this system is still far from being optimal, and pathways towards its improvement are discussed.

Hygroscopic lithium-bis(trifluoromethane)sulfonimide (Li-TFSI) and corrosive pyridine doped 2,2′,7,7′-tetrakis(N,N-di-p-methoxy-phenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) in perovskite solar cells generally results in poor device ambient stability due to moisture-induced degradation of the perovskite absorber. Simultaneously fulfilling good ambient stability and high efficiency, this work proposes the use of a p-type and highly conductive reduced graphene oxide (RGO) reduced by ferrous iodide acid solution, combined with dopant-free spiro-OMeTAD as a hole extraction and transport material in perovskite solar cells, achieving a maximum power conversion efficiency (PCE) of 10.6%, greatly outperforming the reference devices based on pure dopant-free spiro-OMeTAD (PCE = 6.5%). Impressively, only a 15% PCE degradation is observed for the device with RGO/dopant-free spiro-OMeTAD without encapsulation after 500 h, whereas the PCE drops by 65% for the device with Li-TFSI and pyridine doped spiro-OMeTAD. This work represents a significant step toward the realization of stable and high-efficiency perovskite solar cells.

3D hierarchical cobalt hydroxide carbonate hydrate (Co(CO3)0.5(OH)·0.11H2O) has been synthesized featuring a hollow urchin-like structure by a one-step hydrothermal method at modest temperature on FTO glass substrates. The functionalities of precursor surfactants were isolated and analyzed. A plausible formation mechanism of the spherical urchin-like microclusters has been furnished through time-dependent investigations. Introduction of other transitional metal doping (Cu, Ni) would give rise to a substantial morphological change associated with a surface area drop. The directly grown cobalt-based hydroxide composite electrodes were found to be capable of catalyzing oxygen evolution reaction (OER) under both neutral pH and alkaline conditions. The favorable 3D dendritic morphology and porous structure provide large surface areas and possible defect sites that are likely responsible for their robust electrochemical activity.

An inorganic layer and dye molecules have synergistically suppressed the recombination in a quantum dot sensitized solar cell (QDSSC), by the design of a structure featured TiO2–CdS–ZnS–N3 (N3: RuL2(NCS)2 (L = 2,2′-bipyridyl-4,4′-dicarboxylic acid)) hybrid photoanode. When fabricated into solar cells, a cobalt complex-based electrolyte rather than an iodine-based one was employed to obtain an impressive photostability for the devices. Raman and Photoluminescence (PL) measurements revealed that not only the CdS QDs were passivated by both the inorganic layer of ZnS and dye molecule of N3, but also N3 served as an efficient hole scavenger for the CdS QDs due to a type-II energetic alignment between the two sensitizers. This role of N3 as an intermediary in hole extraction from CdS QDs to the electrolyte was further proven by the significant photovoltaic performance improvement of the CdS sensitized solar cell after ZnS deposition and N3 co-sensitization. The overall efficiency of the solar cell incorporated with TiO2–CdS–ZnS–N3 film exceeded the sum of the single CdS QDs and N3 dye sensitized solar cells. This enhancement is ascribed mainly to the synergistic recombination suppression by the inorganic layer ZnS and N3 co-sensitization, leading to inhibited recombination and increased electron lifetime, as illustrated by the electrochemical impedance spectroscopy (EIS) analysis.

The Assembly of one-dimensional (1D) nanostructures such as nanowires/nanorods/nanotubes into two-dimensional (2D) macrostructured films is attracting considerable research interest because of their unique properties and wide applications. In this study, flexible membranes were successfully fabricated using α-MnO2 nanowires synthesized through a hydrothermal method. The effects of thickness and post-annealing temperature on the mechanical properties of the membranes were investigated in detail. Nano-indentation measurements showed that the modulus of the as-prepared 11.75 μm-thick membrane reached 5.765 GPa, and the modulus increased with the increasing post-annealing temperature. Thus, the fabricated membranes with superior mechanical strength can have potential applications such as in photocatalysis, filtering, and supporting substrates.

Two organic sulfide redox couples derived from 2-mercapto-5-methyl-1,3,4-thiadiazole (McMT): tetrabutylammonium thiolate (McMT−TBA+)/disulfide dimer (BMT) and tetramethylammonium thiolate (McMT−TMA+)/BMT were incorporated into quantum dots sensitized solar cells (QDSCs) as alternatives to the inorganic polysulfide electrolyte (Na2S/S). It was found in symmetrical cells test that the interfaces of the organic sulfide electrolytes/platinum counter-electrode have much lower charge transfer resistances as well as higher interface reaction rates compared with that for the inorganic one. Besides, QDSCs based on organic sulfide electrolytes exhibited obviously higher fill factors, open circuit photovoltages, and therefore higher conversion efficiency, thanks to the prohibited recombination and lower redox potential. In addition, by comparing and analyzing the performance of devices based on organic sulfide electrolytes with different cationic groups, it is found that cationic group TMA+ with smaller size was favorable for the mass transport in the electrolyte, which explains the better photovoltaic performance of McMT−TMA+/BMT based solar cell than that of McMT−TBA+/BMT based one. Eventually, a power conversion efficiency (PCE) of 0.63 % was achieved for QDSCs using McMT−(TMA+)/BMT redox couple as electrolyte, which was till now the highest for CdS QDSC based on organic sulfide electrolyte.

Cu2ZnSnS4 (CZTS) nanocrystals were synthesized successfully by two hot-injection methods, for which it was found that the temperature for sulfur precursor injection is an important factor to determine the morphology of nanocrystals. Injection carried out at a lower temperature lead to more homogeneous samples. Pure kesterite CZTS with diameter of about 15–20 nm was achieved confirmed by comprehensive characterizations including TEM, XRD, Raman, and XPS. Besides, CZTS nanocrystal based thin film, which was fabricated by solution process, exhibited a hole mobility of 4.3 × 10−2 cm2/V-s. The film was then successfully incorporated into a Schottky solar cell, yielding an open circuit voltage of about 300 mV. It is notable that this was the first time that the completely nontoxic Schottky solar cell was achieved based on CZTS nanocrystal, which was fabricated completely under room temperature.Cu2ZnSnS4 (CZTS) nanocrystals were synthesized successfully by two hot-injection methods. It was found that sulfur precursor injection carried out at a lower temperature lead to more homogeneous samples. Schottky solar cell based on CZTS nanocrystal with the open circuit voltage of 300 mV was achieved, which was fabricated completely under room temperature for the first time.

Developing metal-free electrocatalysts with both high performance and low cost for the reduction reaction at the cathode of dye-sensitized solar cells (DSCs) is critical for further cost reduction and large-scale implementation of DSCs. Here, sulfur-doped reduced graphene oxide (SRGO) and nitrogen and sulfur dual-doped reduced graphene oxide (NSRGO) were applied as highly efficient metal-free electrocatalysts for DSCs in disulfide/thiolate redox electrolytes. It was found that SRGO and NSRGO exhibited outstanding electrochemical performance toward catalyzing the disulfide/thiolate redox couple. The DSC devices based on SRGO and NSRGO counter electrodes showed power conversion efficiency of 4.23% and 4.73%, respectively. In addition, the obtained SRGO and NSRGO also presented catalytic activity higher than that of the platinum electrodes for Co(bpy)33+/2+ redox mediators. The currently reported SRGO and NSRGO demonstrate not only the attractive feasibility of replacing platinum cathodes with abundant carbon materials for novel iodine-free electrolytes but also that the judicious heteroatom doping of graphene oxide might open promising directions for further cathode candidates for iodine-free DSCs.

Over the last decades, iodine-free redox couples have been widely investigated as alternatives for the ubiquitous triiodide/iodide redox shuttle in dye-sensitized solar cells (DSCs). This is mainly motivated by desires to overcome the disadvantages associated with the latter, such as large energy loss in the dye regeneration process, visible light absorption and corrosiveness towards current-collecting metal grids. However, conventional Pt cathodes show poor catalytic activity towards those iodine-free redox couples, resulting in poor fill factors and relatively moderate power conversion efficiencies. The ultimate solution to address this challenge is to develop alternative economical Pt-free catalysts. This review selectively discusses and summarizes the recent advances in novel cathode materials for electrolytes free of iodine-based redox couples, mainly including inorganic transition metal compounds, organic conductive polymers and carbonaceous materials (particularly carbon nanotubes and graphene). Most of these advances have been realized by judiciously controlling the morphology of nanomaterials or by utilizing the collective properties of nano-assembly systems. Finally, this review highlights the importance of matchup between catalysts and the redox couples, and points to crucial issues that should be addressed in the pursuit of developing low-cost and high-catalytic cathodes for DSCs.

Molecular modification is certified as a powerful strategy to adjust the energy alignment and electron transfer dynamics of dye-sensitized solar cells (DSCs). Herein, devices are assembled with three robust solvent (3-methoxypropionitrile, N,N-dimethylformamide and γ-butyrolactone) based electrolytes to elucidate the solvent dipole effects at the semiconductor–dye–electrolyte interface. Photovoltaic results demonstrate that open-circuit photovoltages of the devices vary linearly with the dipole moment of the solvents, along with an adverse dependence of the short-circuit photocurrent density under simulated irradiation. Impedance analysis reveals an apparent dipole moment-modulated conduction band edge shift of the nanocrystalline TiO2 electrodes with respect to the redox potential of the electrolyte. Furthermore, the adverse shifts of the short-circuit photocurrent are explained by a dipole dependence of the driving force for electron injection and the interfacial charge recombination, together with a notably changed charge collection efficiency. Therefore, this study draws attention to the feasibility of tuning the electron transfer dynamics and energy alignment in photoelectrochemical devices by judiciously selecting the electrolyte solvents for further efficiency improvement, especially for those alternative organic sensitizers or quantum dots with inadequate electron injection driven forces.

Hierarchical Au–Co(OH)2 microclusters have been synthesized by a facile ethanol-assisted hydrothermal method on FTO glass substrates. The as-fabricated Au–Co(OH)2 forms a typical wreath-shaped structure on a nanosheet with an urchin-like Au–Co(OH)2 structure located in the centre surrounded by densely grown Co(OH)2 nanoarrays. Morphological evolution of the Au–Co(OH)2 microclusters through intermediate steps could be identified by varying the reaction time. The incorporated electronegative Au may be responsible for the decrease of binding energy of Au–Co(OH)2 compared to Co(OH)2. The Au–Co(OH)2 electrode was found to be a promising catalyst for the oxygen evolution reaction (OER) in neutral pH solutions, with a larger roughness factor, lower OER onset and much higher current density than a Co(OH)2 electrode. The improvement of the OER activity of Au–Co(OH)2 microclusters may be due to their large surface area provided by the 3D network of microclusters, and the incorporation of Au as an electron sink to facilitate the oxidation of Co(II) and Co(III) to Co(IV).

Four kinds of small molecules with different proton numbers including phenylphosphonic acid (PPA), diphenylphosphinic acid (DPPA), phosphoric acid triethyl ester (PATEE), and phosphorical acid tributyl ester (PATBE) were employed as co-adsorbents of dye sensitized solar cell (DSC). They were innovatively pre-adsorbed onto the nanocrystalline TiO2 surface before dye molecule sensitization, which were detected from X-ray photoelectron spectrum (XPS). Combined with UV–vis absorption analysis, it was found the co-adsorbents got to bind with TiO2 more and more easily by increasing proton numbers, which in turn made dye loading amount get smaller and smaller. The as-prepared photoanodes were fabricated into solar cells, yielding impressively enhanced short-circuit current and cell efficiency except PPA which decreased the dye loading amount dramatically. The enhancement of charge recombination resistance and electron lifetime analyzed from EIS results revealed that the more prominent photovoltaic performance improvement with fewer protons was resulted by the more efficient inhibition of recombination between electrons in the conduction band of TiO2 and the oxidized species in the electrolyte. Besides, regarding from the charge transport resistance, fewer protons are favorable for the negative shift of the conduction band level of TiO2 and thus larger open-circuit yielding.

The electrochemical properties of Co–Ni layered double hydroxides (LDHs) as efficient electrocatalysts for water oxidation were investigated in potassium phosphate electrolyte under neutral pH condition. The Co–Ni LDHs with a core–shell structure were fabricated using a facile route from a Co–Ni hydroxide precursor with iodine as a topotactic oxidizer. The unique core–shell morphology is likely due to the enrichment of Co(III) hydroxide in the inner core indicated by selected area electron diffraction and energy-dispersive spectroscopy. Through a self-assembling process at the organic/inorganic interface and dip-coating, the Co–Ni LDHs were deposited onto FTO glass substrates to prepare composite electrodes. Low over-potential and high current density was achieved in the oxygen evolution reaction. The excellent electrocatalytic activity of Co–Ni LDHs may be attributed to more accessible Co active sites and rapid movement of interlayer ions within their layered structure.

Type-II heterostructure CdTe/CdSe core/shell nanocrystals (quantum dots, QDs) are explored as sensitizers in a QD-sensitized photoelectrochemical solar cell. These QDs comprise a hole-localizing core and an electron-localizing shell. Among their advantages is the significant red shift of the absorption edge of the heterostructured QD relative to its two constituents due to spatially indirect absorption leading to improved absorption characteristics, intraparticle exciton dissociation upon photoexcitation, and a relatively small content of the less abundant tellurium element. Upon incorporation in a sensitized solar cell utilizing a porous TiO2 and a polysulfide electrolyte, these QDs exhibited efficient charge separation and high internal quantum efficiency despite hole localization in the CdTe core. Monochromatic incident photon-to-current conversion efficiency (IPCE) measurement shows a spectrally broad photoresponse spanning the whole visible spectrum and reaching up to ∼900 nm.

Searching for suitable platinum-free electrocatalysts toward novel iodine-free redox couples is of vital importance for further cost reduction and large-scale implementation of dye-sensitized solar cells (DSCs). Herein, cross-stacked superaligned carbon nanotube (CSCNT) sheets were incorporated as efficient economical cathodes in organic disulfide/thiolate redox electrolyte mediated DSCs. Electrochemical characterization revealed that the CSCNT sheets exhibited notably higher electrocatalytic activity toward the disulfide/thiolate redox shuttle over that of ubiquitous platinized cathodes, featuring a significantly decreased charge transfer resistance (ca. 1.26 Ω cm2) and a 4-fold attenuated apparent activation energy (ca. 6.90 kJ mol−1) for disulfide reduction, as well as excellent electrochemical stability. Such a superior electrocatalytic activity was mainly attributed to the synergistic effect of the high specific surface area, relatively open structure for electrolyte accessibility and defect-rich CSCNT cathode. A device incorporating a CSCNT cathode confers a high fill factor of 0.67 and power conversion efficiencies up to 5.81%, which are significantly higher than 0.54 and 4.54% for that with a sputtered Pt cathode. Our investigations demonstrate not only the attractive feasibility of replacing scarce platinum cathodes with abundant carbon materials for novel iodine-free electrolytes, but also the importance of suitable catalyst redox coupling for progress in developing low-cost and high-efficiency DSCs.

AlI3 synthesized by I2 and Al in ethanol was used as reductive agent to directly obtain flexible reductive graphene oxide (RGO) films with high conductivity of 5320 S/m from graphene oxide (GO) films at a low temperature of 80 °C. This reductive method has provided a low-cost and effective route for large-scale production of graphene with high catalytic activity. Structural evolution during the reduction of GO was studied by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. The RGO films served as counter electrode exhibited high electrochemical activity.

Nitric acid was added to binder-free TiO2 paste for the preparation of plastic TiO2 dye-sensitized photoanode at low temperature on conductive indium–tin oxide (ITO)-coated polyethylene naphthalate (PEN) substrate. The influence of nitric acid on the electron transport within the cells was scrutinized. It was found that the electron transport was accelerated by means of increasing nitric acid contents. Rheological behavior testing revealed that the increasing concentration of nitric acid leaded to a decrease of viscosity of the paste and then increased the coordination number within the photoanode, which represent the possible electron transfer pathways in the photoanode. This was confirmed by scanning electronic microscopy (SEM) results. Electrochemical impedance spectroscopy (EIS) results showed that the charge transport resistance in the TiO2 film (Rt) decreased gradually when the nitric acid content increased from 0 to 0.1 M, which was attributed to the increasing coordination number of TiO2 particles in the nanoporous film. Meanwhile, the increasing NO3− will prohibit the electron recombination between TiO2 and electrolyte proved by EIS measurements. However, excessive nitric acid also leaded to a corrosion of the ITO substrate and impaired the photovoltaic performance of the flexible devices. Hence, the devices prepared with nitric acid content of 0.025 M achieved the highest overall energy conversion efficiency of 5.30%.

Ethynyl-linked porphyrin hetero-dimers substituted by a series of electron donors, namely, bis(4-methoxyphenyl)amino (BMPA), bis(4-tert-butylphenyl)amino (BTBPA) and 3,6-di-tert-butylcarbazol-9-yl (DTBC) as well as a reference dimer with a non-donor moiety (3,5-di-tert-butylphenyl, DTBP) have been synthesized to systematically investigate the influence of donor introduction on the photovoltaic performances of near-IR dye-sensitized solar cells (DSCs) with these sensitizers incorporated. Despite the expected bathochromic shift and intensification of long-wavelength absorption bands as well as elevated LUMO levels and thus increased electron injection driving forces, the substitution of diphenylamino groups (BMPA and BTBPA) with stronger electron-donating abilities gave rise to surprising mediocrity in the short-circuit photocurrent densities (Jsc), leading to overall energy conversion efficiencies in the order BMPA (3.94%) < DTBP (4.57%) < BTBPA (4.83%) < DTBC (5.21%). A study of the in situ fluorescent behavior of these sensitizers revealed that for all the sensitizers, excited-state lifetimes were significantly shortened in the simulated DSC environment compared to those in a free solution. BMPA showed the shortest intrinsic in situ lifetime while DTBC showed the longest one. These results were correlated with the photovoltaic performances, which is required for a better understanding and further design of porphyrin array sensitizers.

A highly efficient quantum dot (QD)/inorganic layer/dye molecule sandwich structure was designed and applied in electrochemical QD-sensitized solar cells. The key component TiO2/CdS/ZnS/N719 hybrid photoanode with ZnS insertion between the two types of sensitizers was demonstrated not only to efficiently extend the light absorption but also to suppress the charge recombination from either TiO2 or CdS QDs to electrolyte redox species, yielding a photocurrent density of 11.04 mA cm–2, an open-circuit voltage of 713 mV, a fill factor of 0.559, and an impressive overall energy conversion efficiency of 4.4%. More importantly, the cell exhibited enhanced photostability with the help of the synergistic stabilizing effect of both the organic and the inorganic passivation layers in the presence of a corrosive electrolyte.

With a comparable specific surface area, 17% enhanced dye-loading capacity was observed for the first time in the (001) faceted TiO2 single crystals compared to that of benchmark P25 nanoparticles, thus generating a significant enrichment in both short-circuit photocurrent density and power conversion efficiency of dye-sensitized solar cells (DSCs). Such a remarkably increased dye-loading capacity was primarily ascribed to the higher density of 5-fold-coordinnated Ti atoms on the (001) surfaces. Furthermore, kinetic studies revealed that such single crystals confer a higher electron lifetime and charge collection efficiency compared with conventional P25 electrode, which might originate from the specific surface configuration in these high energetic facet dominant single crystals. Our study provides straightforward evidence for the superior reactivity of (001) facets and implies that such single TiO2 crystals with high-energetic facets would be a promising electrode material for DSCs.

A novel dye-sensitized solar cell (DSSC) structure using vertically aligned single-walled carbon nanotubes (VASWCNTs) as the counter electrode has been developed. In this design, the VASWCNTs serve as a stable high surface area and highly active electrocatalytic counter-electrode that could be a promising alternative to the conventional Pt analogue. Utilizing a scalable dry transfer approach to form a VASWCNTs conductive electrode, the DSSCs with various lengths of VASWCNTs were studied. VASWCNTs-DSSC with 34 μm original length was found to be the optimal choice in the present study. The highest conversion efficiencies of VASWCNTs-DSSC achieved 5.5%, which rivals that of the reference Pt DSSC. From the electrochemical impedance spectroscopy analysis, it shows that the new DSSC offers lower interface resistance between the electrolyte and the counter electrode. This reproducible work emphasizes the promise of VASWCNTs as efficient and stable counter electrode materials in DSSC device design, especially taking into account the low-cost merit of this promising material.Keywords: counter electrodes; dye-sensitized solar cells; electrocatalytic activity; vertically aligned single-walled carbon nanotubes;

To improve the mechanical rigidity of the electrocatalyst and assure a higher number density of catalytic sites of the counter electrode in dye-sensitized solar cells (DSCs), we have extended widely applied titanium tetrachloride treatment to construct a rough scaffolding underlayer for the platinized counter electrode. Field-emission scanning electron microscopy and atomic force microscopy images clearly depicted the platinum nanoparticles with a diameter of ca. 10 nm homogeneously distributed on the scaffolding underlayer of the bilayer counter electrode and thus led to a characteristically high surface roughness. The electocatalytic activity of this novel bilayer counter electrode was measured and compared with the corresponding properties of conventional sputtered Pt electrode. Interestingly, electrochemical impedance spectroscopy and cyclic voltammetry measurements further demonstrated the notably larger electrochemical active surface area and thereby higher electrocatalytic activity of the bilayer counter electrode. Consequently, under standard 1 sun illumination (100 mW cm-2, AM 1.5), device with this bilayer counter electrode achieved a considerably improved fill factor of 0.67 and overall energy conversion efficiency of 7.09%, which was apparently higher than that of 0.60 and 6.37% for sputterd Pt electrode. Therefore, this present method paves a facile and inexpensive way to prepare high-electrocatalytic bilayer counter electrode in DSCs.Keywords: charge transfer resistance; counter electrode; dye-sensitized solar cells; electrocatalytic activity; electrochemical active surface area; titanium tetrachloride treatment;

Anhydrous AlCl3 was used to increase the reducing ability of sodium borohydride (NaBH4) for removing oxygen functional groups on graphene oxide (GO) at a reaction temperature below 150 °C, which provided an extendable, mild, and controllable route for large-scale production of graphene. The influences of reducing temperature and reducing time on the electrical conductivity of reduced GO were examined. Structural evolution during the reduction of GO was studied by Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Raman spectroscopy, and elemental analysis.

Diphenylphosphinic acid (DPPA) was adopted as a novel coadsorbent in dye-sensitized solar cells (DSCs) based on nanocrystalline TiO2 sensitized with N719 dye [(Bu4N)2[Ru(dcbpyH)2(NCS)2]], leading to a significant enhancement of the cell's performance. Different ratios of dye-to-coadsorbent caused varying results, including a 12.5% increase in overall conversion efficiency coupled with a 10.6% increase in short-circuit current with a ratio of 2:1. Electrochemical impedance spectroscopy (EIS) results indicated that the augment ascribes to inhibited interfacial charge recombination between the conduction band electrons and triiodide ions in the electrolyte. On the other hand, different ratios caused different shift directions of the TiO2 conduction band, which was confirmed by charge transport resistance obtained also from EIS analysis. To be specific, when the ratio of N719-to-DPPA was 2:1 and 1:1, the conduction band of TiO2 film was positively shifted, while it was negatively shifted when the ratio was 4:1.

The compression method was applied for the preparation of plastic TiO2 porous films on a conductive indium–tin oxide (ITO)-coated polyethylene naphthalate (PEN) substrate at low temperature for the generation of high-efficiency plastic dye-sensitized solar cells (DSCs). The compression parameters, including pressure and time, were varied in order to determine their effect on the photovoltaic performance of the plastic DSCs. The results from electrochemical impedance spectroscopy (EIS) showed that charge transport resistance in the porous TiO2 films (Rt) gradually decreased when the applied pressure was increased from 0 MPa to 150 MPa, which indicated a better connection between the TiO2 nanoparticles and electron transport in the TiO2 films. In addition, a longer press time led to an increased resistance of electron recombination (Rct) and an increased charge-collection efficiency. After optimization of the compression parameters, the efficiency of energy conversion was increased by approximately 81.6%. In addition, the efficiency of energy conversion was increased by an additional 4.65% under AM1.5 illumination.

Alkyl-substituted pyridinium iodide has been applied as alternative iodide source in dye-sensitized solar cells (DSCs), featuring impressively high diffusivity and electroactivity. Encouraging energy conversion efficiency up to 8.23% was achieved, implying that this alkylpyridinium iodide serves as an effective alternative iodide source for DSCs. The intensity-modulated photocurrent/photovoltage spectroscopy measurements further indicated that the electron diffusion coefficient was considerably enhanced in device with pyridinium iodide electrolyte in comparison with that of the conventional imidazolium iodide, which was primarily due to a more shallow distribution of the surface trap states after the adsorption of pyridinium cations on the TiO2 electrode surface.Research Highlights► Alternative efficient alkylpyridinium iodide in dye-sensitiezed solar cells. ► High ionic conductivity and electroactivity. ► Overall energy conversion efficiency up to 8.23%. ► Enhanced electron diffusion coefficient and charge collection efficiency.

To mitigate the mass transfer limitations of a highly viscous room temperature ionic liquid (RTIL) electrolyte, systematic characterizations of viscosity, ionic conductivity, apparent triiodide diffusion coefficient and photovoltaic response of an alternative cost-effective and highly conductive binary RTIL mixture of 1-ethyl-3-methylimidazolium trifluoroacetate (EMIATF) and 1-methyl-3-propylimidazolium iodide (PMII) were investigated. An emphasis was placed on the dynamics of electron transport and charge recombination processes; specifically, a focus was placed on the effective electron diffusion length and charge collection efficiency in the devices. Notably, the introduction of perfluorinated anions, with a strong delocalization of the negative charge over the anion backbone, was able to weaken the hydrogen bonding with the imidazolium cations and, thus, decrease the viscosity and increase the ionic conductivity of the electrolyte. A sealed device that employed the binary RTIL achieved an overall conversion efficiency of 5.22% under irradiation of 100 mW cm−2, which increased the value by 30% compared to a device with a blank PMII-based RTIL electrolyte. Electrochemical impedance spectroscopy and intensity-modulated photovoltage/photocurrent spectroscopy analysis revealed that employment of this alternative binary RTIL electrolyte system was able to significantly decrease the diffusion resistance of triiodide species in the electrolyte and retard the charge recombination between the injected electrons with triiodide anions in the electrolyte, thus improving the effective electron diffusion length and charge collection efficiency in the device. The charge collection efficiency was certified to be the dominant parameter governing the short-circuit photocurrent density and the overall conversion efficiency of devices with RTIL electrolyte.Highlights► Cost-effective and highly conductive binary ionic liquids electrolyte. ► Dynamics of electron transport and charge recombination processes. ► Significantly decreased diffusion resistance and retarded charge recombination. ► Improving the effective electron diffusion length and charge collection efficiency.

Room temperature ionic liquids (RTILs) have been used as electrolytes to investigate the anionic structure dependence of the photoelectrochemical responses of dye-sensitized solar cells (DSCs). A series of RTILs with a fixed cation structure coupling with various anion structures are employed, in which 1-methyl-3-propylimidazolium iodide (PMII) and I2 are dissolved as redox couples. It is found that both the diffusivity of the electrolyte and the photovoltaic performance of the device show a strong dependence on the fluidity of the ionic liquids, which is primarily altered by the anion structure. Further insights into the structure-dependent physical properties of the employed RTILs are discussed in terms of the reported van der Waals radius, the atomic charge distribution over the anion backbones, the interaction energy of the anion and cation, together with the existence of ion-pairs and ion aggregates. Particularly, both the short-circuit photocurrent and open-circuit voltage exhibit obvious fluidity dependence. Electrochemical impedance and intensity-modulated photovoltage/photocurrent spectroscopy analysis further reveal that increasing the fluidity of the ionic liquid electrolytes could significantly decrease the diffusion resistance of I3− in the electrolyte, and retard the charge recombination between the injected electrons with triiodide in the high-viscous electrolyte, thus improving the electron diffusion length in the device, as well as the photovoltaic response. However, the variation of the electron diffusion coefficients is trivial primarily due to the effective charge screening of the high cation concentration.

A novel heterostructural TiO2 nanocomposite, which consists of single-crystalline rutile TiO2 nanorod decorated Degussa P25 nanoparticles, has been fabricated through a facile acidic hydrothermal method and successfully applied as the photoanodes for efficient dye-sensitized solar cells. The morphology, crystal structure, specific surface area and pore size distribution of the obtained nanocomposite were systematically investigated by X-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), high resolution transmission electron microscope (HRTEM), selected-area electron diffraction patterns (SAED) and nitrogen adsorption–desorption measurements. Under standard illumination conditions (AM 1.5, 100 mW cm−2), devices with these hybrid anodes exhibited considerably enhanced photocurrent density and overall conversion efficiency in comparison with that of the commercial Degussa P25 electrodes, which can be partially attributed to the light scattering effect in the long-wavelength region as evidenced from the incident photon-to-current conversion efficiency (IPCE) response and the diffuse reflectance spectroscopy. More importantly, devices employing these hybrid anodes have demonstrated extended electron lifetimes and larger electron diffusion coefficient as validated by the intensity-modulated photocurrent/photovoltage spectroscopy measurements, which can be mainly ascribed to the fast electron transport and collection superiority of the single-crystalline nanorods.

Surface treatment of ruthenium dye (Bu4N)2[Ru(dcbpyH)2(NCS)2]-sensitized TiO2 films using diethyl 4-methylphenylphosphonate as a coadsorbent results in large improvements in DSC performance, 24% larger overall conversion efficiency and 55 mV higher open-circuit voltage without current penalty. Introducing another two coadsorbents ethyl 4-methylphenylphosphonate and 4-methoxyphenylphosphonic acid brings in negative effects. Analysis by impedance spectroscopy indicated that this was attributed to different numbers of proton-releasing hydroxyl groups of the coadsorbents and consequently different proton-adsorbing chemical environments on the surface of TiO2 photoanodes.Research highlights► Dye-sensitized solar cell. ► Proton release. ► Conduction-band shift. ► Surface passivation.

The influences of molding pressures, bonding phase contents, and SiC particle sizes on the flexural strength of SiC-based porous ceramics were investigated based on their microstructure of fracture surface. The SEM morphologies and EDS element analysis results of fracture surface showed that there were two different kinds of fracture points: SiC particle fracture points and bonding phase fracture points. It is found that molding pressures, bonding phase contents, and SiC particle sizes affect the SiC particle fracture point area in the fracture surface, and the fraction of the SiC particle fracture point area in the minimum solid area of fracture surface is a determined influence factor for the flexural strength of SiC-based porous ceramics used for hot gas filter support.

A titanate nanofiber paper with robust and good flexible property was successfully prepared by alkali hydrothermal synthesis with simple paper-making method. These nanofibers were about 80 nm in diameter and had a typical length in the range of tens of micrometers. Despite the transformation from titanate to TiO2-B phase was initially started, such nanofiber paper still kept its original shape and good flexibility after calcinations at 450 °C for 30 min. A solar cell with titanate nanofiber paper as scattering layer yielded an overall conversion efficiency of 4.90% under an incident solar energy of 100 mW/cm2, about 27.5% higher than that without nanofiber paper.

Promoted by the growing concerns about the worldwide energy demand and global warming, dye-sensitized solar cells (DSSCs) are currently attracting worldwide scientific and technological interest because of their high energy conversion efficiency and simple fabrication process. Considering long-terms stability and practice applications, growing attentions have been paid to non-volatile, 3-methoxyproprionitrile (MPN)-based electrolyte, ionic liquids (ILs) electrolyte, as well as quasi-solid state electrolyte. In this present review, recent progress in electrolyte for DSSCs made by our group are summarized, including component-optimization of the non-volatile electrolyte, the fluidity-dependent charge transport mechanism in the binary IL electrolytes as well as the structure dominance of the employed ILs. Furthermore, progress on the quasi-solid state electrolyte based on inorganic nanomaterials as gelators in our group has also been outlined.

Lanthanum (La) has been used for the first time as an additive in the sol–gel precursor lithium aluminosilicate (Li2O–Al2O3–2SiO2) to prepare β-eucryptite at different temperatures. The influence of La additive on the phase transition of β-eucryptite was studied by X-ray diffraction and differential scanning calorimetry. Scanning electron microscope analysis showed that plenty of large aspect ratio rod-like β-eucryptite was formed in the sample containing La additive at 1180 °C, and then gradually disappeared at higher sintering temperature. The La additive formed a low-temperature liquid phase LiLaSiO4 and promoted the crystal growth of β-eucryptite at 1350 °C. Li+ conductivity of bulk β-eucryptite with La additive was higher than that without La additive below 603 K.

A mesoporous TiO2 film consisting of different size nanocrystal particles without any organic binder was prepared on a conductive indium−tin oxide (ITO)-coated polyethylene naphthalate (PEN) plastic sheet by the doctor-blade method to fabricate flexible dye-sensitized photoanodes at 120 °C. It was found that the structure of the film affected the photovoltaic performance of the photoanode greatly. The mechanism of such effects was investigated both by simulation of porosity, surface area, average pore size, and electron diffusion coefficient of the mesoporous TiO2 film, and by impedance study for the electron transport and recombination in a dye-sensitized solar cell (DSC). The results showed that the electron transport and recombination dominated the operation of the DSC with such flexible photoanodes. The optimum photoanode was achieved, and the largest conversion efficiency obtained was 3.93%.

A porous electrode was prepared by introduction of indium tin oxide (ITO) into pores of a porous glass (PG) matrix with nano-size pores and thus forming an ITO/PG nanocomposite, using metallorganic chemical vapor deposition (MOCVD) method. The ITO/PG nanocomposite has through pores and a specific surface area of about 7.6×104 times larger than that of a plane transparent conductive glass. The porous electrode is suggested to be a good candidate of electrode used in photoelectric devices.

Ethynyl-linked porphyrin hetero-dimers substituted by a series of electron donors, namely, bis(4-methoxyphenyl)amino (BMPA), bis(4-tert-butylphenyl)amino (BTBPA) and 3,6-di-tert-butylcarbazol-9-yl (DTBC) as well as a reference dimer with a non-donor moiety (3,5-di-tert-butylphenyl, DTBP) have been synthesized to systematically investigate the influence of donor introduction on the photovoltaic performances of near-IR dye-sensitized solar cells (DSCs) with these sensitizers incorporated. Despite the expected bathochromic shift and intensification of long-wavelength absorption bands as well as elevated LUMO levels and thus increased electron injection driving forces, the substitution of diphenylamino groups (BMPA and BTBPA) with stronger electron-donating abilities gave rise to surprising mediocrity in the short-circuit photocurrent densities (Jsc), leading to overall energy conversion efficiencies in the order BMPA (3.94%) < DTBP (4.57%) < BTBPA (4.83%) < DTBC (5.21%). A study of the in situ fluorescent behavior of these sensitizers revealed that for all the sensitizers, excited-state lifetimes were significantly shortened in the simulated DSC environment compared to those in a free solution. BMPA showed the shortest intrinsic in situ lifetime while DTBC showed the longest one. These results were correlated with the photovoltaic performances, which is required for a better understanding and further design of porphyrin array sensitizers.

Hygroscopic lithium-bis(trifluoromethane)sulfonimide (Li-TFSI) and corrosive pyridine doped 2,2′,7,7′-tetrakis(N,N-di-p-methoxy-phenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) in perovskite solar cells generally results in poor device ambient stability due to moisture-induced degradation of the perovskite absorber. Simultaneously fulfilling good ambient stability and high efficiency, this work proposes the use of a p-type and highly conductive reduced graphene oxide (RGO) reduced by ferrous iodide acid solution, combined with dopant-free spiro-OMeTAD as a hole extraction and transport material in perovskite solar cells, achieving a maximum power conversion efficiency (PCE) of 10.6%, greatly outperforming the reference devices based on pure dopant-free spiro-OMeTAD (PCE = 6.5%). Impressively, only a 15% PCE degradation is observed for the device with RGO/dopant-free spiro-OMeTAD without encapsulation after 500 h, whereas the PCE drops by 65% for the device with Li-TFSI and pyridine doped spiro-OMeTAD. This work represents a significant step toward the realization of stable and high-efficiency perovskite solar cells.

A novel heterostructural TiO2 nanocomposite, which consists of single-crystalline rutile TiO2 nanorod decorated Degussa P25 nanoparticles, has been fabricated through a facile acidic hydrothermal method and successfully applied as the photoanodes for efficient dye-sensitized solar cells. The morphology, crystal structure, specific surface area and pore size distribution of the obtained nanocomposite were systematically investigated by X-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), high resolution transmission electron microscope (HRTEM), selected-area electron diffraction patterns (SAED) and nitrogen adsorption–desorption measurements. Under standard illumination conditions (AM 1.5, 100 mW cm−2), devices with these hybrid anodes exhibited considerably enhanced photocurrent density and overall conversion efficiency in comparison with that of the commercial Degussa P25 electrodes, which can be partially attributed to the light scattering effect in the long-wavelength region as evidenced from the incident photon-to-current conversion efficiency (IPCE) response and the diffuse reflectance spectroscopy. More importantly, devices employing these hybrid anodes have demonstrated extended electron lifetimes and larger electron diffusion coefficient as validated by the intensity-modulated photocurrent/photovoltage spectroscopy measurements, which can be mainly ascribed to the fast electron transport and collection superiority of the single-crystalline nanorods.

ZnTe, a non-toxic low band gap semiconductor, has a direct band gap of 2.26 eV, and can be a promising candidate for non-toxic semiconductor sensitized solar cells (SSSCs). Herein, we report a simple and low-cost solution-processing approach to synthesize ZnTe nanocrystals by using dendrite-like ZnO nanorods as templates via an in situ method for application in solar cells. Structural and morphological analyses and systematic optical property investigations evidenced the successful synthesis of ZnTe nanocrystals and ZnO/ZnTe heterostructures. The measured band alignment of the heterostructures directly points to the strong effect of strain and the possibility to engineer the band offset at the ZnO/ZnTe interface. As ZnO and ZnTe exhibit a type-II energy level alignment, both significant absorption and efficient charge transfer are enabled between the two. Finally, solar cells based on the ZnO/ZnTe heterostructure were fabricated and a short-circuit photocurrent density of over 5 mA cm−2 was achieved, benefiting from the preeminent absorption, high charge separation and transfer efficiency. A ZnS passivation layer dramatically improved the performance of the solar cells reaching a short-circuit photocurrent density of over 10 mA cm−2, along with an increase in the power conversion efficiency (PCE) from 0.46% to 1.7%. Potential pathways towards further increasing this figure are discussed.

Searching for suitable platinum-free electrocatalysts toward novel iodine-free redox couples is of vital importance for further cost reduction and large-scale implementation of dye-sensitized solar cells (DSCs). Herein, cross-stacked superaligned carbon nanotube (CSCNT) sheets were incorporated as efficient economical cathodes in organic disulfide/thiolate redox electrolyte mediated DSCs. Electrochemical characterization revealed that the CSCNT sheets exhibited notably higher electrocatalytic activity toward the disulfide/thiolate redox shuttle over that of ubiquitous platinized cathodes, featuring a significantly decreased charge transfer resistance (ca. 1.26 Ω cm2) and a 4-fold attenuated apparent activation energy (ca. 6.90 kJ mol−1) for disulfide reduction, as well as excellent electrochemical stability. Such a superior electrocatalytic activity was mainly attributed to the synergistic effect of the high specific surface area, relatively open structure for electrolyte accessibility and defect-rich CSCNT cathode. A device incorporating a CSCNT cathode confers a high fill factor of 0.67 and power conversion efficiencies up to 5.81%, which are significantly higher than 0.54 and 4.54% for that with a sputtered Pt cathode. Our investigations demonstrate not only the attractive feasibility of replacing scarce platinum cathodes with abundant carbon materials for novel iodine-free electrolytes, but also the importance of suitable catalyst redox coupling for progress in developing low-cost and high-efficiency DSCs.

The electrochemical properties of Co–Ni layered double hydroxides (LDHs) as efficient electrocatalysts for water oxidation were investigated in potassium phosphate electrolyte under neutral pH condition. The Co–Ni LDHs with a core–shell structure were fabricated using a facile route from a Co–Ni hydroxide precursor with iodine as a topotactic oxidizer. The unique core–shell morphology is likely due to the enrichment of Co(III) hydroxide in the inner core indicated by selected area electron diffraction and energy-dispersive spectroscopy. Through a self-assembling process at the organic/inorganic interface and dip-coating, the Co–Ni LDHs were deposited onto FTO glass substrates to prepare composite electrodes. Low over-potential and high current density was achieved in the oxygen evolution reaction. The excellent electrocatalytic activity of Co–Ni LDHs may be attributed to more accessible Co active sites and rapid movement of interlayer ions within their layered structure.

Room temperature ionic liquids (RTILs) have been used as electrolytes to investigate the anionic structure dependence of the photoelectrochemical responses of dye-sensitized solar cells (DSCs). A series of RTILs with a fixed cation structure coupling with various anion structures are employed, in which 1-methyl-3-propylimidazolium iodide (PMII) and I2 are dissolved as redox couples. It is found that both the diffusivity of the electrolyte and the photovoltaic performance of the device show a strong dependence on the fluidity of the ionic liquids, which is primarily altered by the anion structure. Further insights into the structure-dependent physical properties of the employed RTILs are discussed in terms of the reported van der Waals radius, the atomic charge distribution over the anion backbones, the interaction energy of the anion and cation, together with the existence of ion-pairs and ion aggregates. Particularly, both the short-circuit photocurrent and open-circuit voltage exhibit obvious fluidity dependence. Electrochemical impedance and intensity-modulated photovoltage/photocurrent spectroscopy analysis further reveal that increasing the fluidity of the ionic liquid electrolytes could significantly decrease the diffusion resistance of I3− in the electrolyte, and retard the charge recombination between the injected electrons with triiodide in the high-viscous electrolyte, thus improving the electron diffusion length in the device, as well as the photovoltaic response. However, the variation of the electron diffusion coefficients is trivial primarily due to the effective charge screening of the high cation concentration.

An inorganic layer and dye molecules have synergistically suppressed the recombination in a quantum dot sensitized solar cell (QDSSC), by the design of a structure featured TiO2–CdS–ZnS–N3 (N3: RuL2(NCS)2 (L = 2,2′-bipyridyl-4,4′-dicarboxylic acid)) hybrid photoanode. When fabricated into solar cells, a cobalt complex-based electrolyte rather than an iodine-based one was employed to obtain an impressive photostability for the devices. Raman and Photoluminescence (PL) measurements revealed that not only the CdS QDs were passivated by both the inorganic layer of ZnS and dye molecule of N3, but also N3 served as an efficient hole scavenger for the CdS QDs due to a type-II energetic alignment between the two sensitizers. This role of N3 as an intermediary in hole extraction from CdS QDs to the electrolyte was further proven by the significant photovoltaic performance improvement of the CdS sensitized solar cell after ZnS deposition and N3 co-sensitization. The overall efficiency of the solar cell incorporated with TiO2–CdS–ZnS–N3 film exceeded the sum of the single CdS QDs and N3 dye sensitized solar cells. This enhancement is ascribed mainly to the synergistic recombination suppression by the inorganic layer ZnS and N3 co-sensitization, leading to inhibited recombination and increased electron lifetime, as illustrated by the electrochemical impedance spectroscopy (EIS) analysis.