Rhodanine-3-acetic acid is a very important and common electron acceptor of organic dye for dye-sensitized solar cells (DSSCs). However, the photovoltaic performances of organic dyes with rhodanine-3-acetic acid are relatively poor in the great majority of cases due to its nonconjugated structure between rhodanine ring and carboxyl anchoring group. Herein, a rhodanine derivative with conjugated structure between rhodanine ring and anchoring group is first employed as electron acceptor for TiO2-based DSSCs. Organic dye with this conjugated electron acceptor can not only maintain wide absorption spectrum but also greatly improve the electronic structure and adsorption geometry on TiO2, which significantly enhances the electron injection and slows the charge recombination. So the power conversion efficiency of DSSC based on organic dye CRD-I with this conjugated electron acceptor is increased by 2 times as compared with DSSC based on organic dye RD-I with nonconjugated rhodanine-3-acetic acid. Moreover, it is also found that CRD-I is superior to RD-I with respect to DSSC stability and binding ability to TiO2. This work unambiguously demonstrates that the conjugated rhodanine derivative is a highly promising electron acceptor and provides a new strategy for high-efficiency rhodanine-based organic dyes in DSSCs.Keywords: adsorption geometry; conjugation structure; dye-sensitized solar cells; electron acceptor; rhodanine derivative;

•Polymer films based on poly(CBZ-TPA) and poly(CBZ-TPA-Th) were synthesized.•The electrochromic properties of the two films were investigated.•The maximum UV–vis absorption modulation of the two films are 15.83% and 23.30%.•The biggest different average IR-emissivity modulation of two films are 0.37 and 0.41.Synthesis and characterizations of novel conducting polymer film based on poly(carbazoyltriphenylamine) (poly(CBZ-TPA)) were studied. Additionally, copolymer film based on CBZ-TPA and thiophene (Th) was also obtained by electrochemical polymerization. Electrochromic properties of poly(CBZ-TPA) and poly(CBZ-TPA-Th) films were investigated by cyclic voltammetry and double step potential chronoamperometry. Optical properties of the two films were characterized by UV–vis spectrophotometer and FT-IR spectrometer. Different colors of poly(CBZ-TPA) film were achieved, which exhibits as camel gray (at −0.5 V), light gray (at 0 V) and army green (at 1.6 V). The maximum UV–vis absorption difference of poly(CBZ-TPA) film is about 15.83% in the visible region when applied with the voltage between 0 V and 1.6 V, and the coloring and bleaching time are 1.8 s and 1.0 s, respectively. The biggest different average IR-emissivity modulation of poly(CBZ-TPA) film is 0.37 in the wavelength regions of 8–14 μm. The copolymerization film of thiophene with CBZ-TPA has a distinct effect on the electrochromic performance of poly(CBZ-TPA) film. Compared with poly(CBZ-TPA) film, poly(CBZ-TPA-Th) film shows different colors, which exhibits as maize-yellow (at −0.5 V), milk white (at 0 V) and dark green (at 1.4 V). The maximum UV–vis absorption difference of poly(CBZ-TPA-Th) film is about 23.30% in the visible region between 0 V and 1.4 V, but it has a slower response speed (coloring and bleaching time are 3.0 s and 4.0 s, respectively). However, the biggest different average IR-emissivity modulation of poly(CBZ-TPA-Th) film reaches up to 0.41 in the wavelength regions of 8–14 μm compared to that of poly(CBZ-TPA) film.Download high-res image (231KB)Download full-size image

•Highly conductive and loose multilayered graphene paper was obtained.•Graphene papers with different parameters were fabricated.•Capacitive performance of the graphene papers was systematically investigated.•Flexible supercapacitor with good electrochemical stability was assembled.For practical applications of graphene-based materials in flexible supercapacitors, a technological breakthrough is currently required to fabricate high-performance graphene paper by a facile method. Herein, highly conductive (∼6900 S m−1) graphene paper with loose multilayered structure is produced by a high-efficiency in-situ chemical reduction process, which assembles graphite oxide suspensions into film and simultaneously conducts chemical reduction. Graphene papers with different parameters (including different types and doses of reductants, different thicknesses and areas of films) are successfully fabricated through this in-situ chemical reduction method. Meanwhile, the influences of the graphene papers with different parameters upon the supercapacitor performance are systematically investigated. Flexible supercapacitor based on the graphene paper exhibits high areal capacitance (152.4 mF cm−2 at current density of 2.0 mA cm−2 in aqueous electrolyte), and excellent rate performance (88.7% retention at 8.0 mA cm−2). Furthermore, bracelet-shaped all-solid supercapacitor with fascinating cycling stability (96.6% retention after 10 000 cycles) and electrochemical stability (an almost negligible capacity loss under different bending states and 99.6% retention after 4000 bending cycles) is established by employing the graphene paper electrode material and polymer electrolyte.Download high-res image (320KB)Download full-size image

•4-methylbenzenesulfonic acid can improve the quality of perovskite film.•4-methylbenzenesulfonic acid can grapple with mesoporous TiO2.•The π-conjugated structure in the additive benefits electron transfer.•The 4-methylbenzenesulfonic acid doped device has a low hysteresis of 0.048.•The optimized device obtains the champion PCE of 17.58%.Grain size of MAPbI3 and thickness of mesoporous TiO2 (mp-TiO2) film are found to influence current-voltage (J-V) hysteresis, where the J-V hysteresis is alleviated as grain size increases and thickness of mp-TiO2 varies. In this work, a low-cost and high-efficiency additive 4-methylbenzenesulfonic acid (4-MSA) is introduced into perovskite precursor solution to improve the performances of perovskite solar cells (PSCs) and reduce the device hysteresis. By adjusting 4-MSA concentration, the fabricated PSC shows the best power conversion efficiency (PCE) of 17.58% (Jsc = 23.15 mA cm−2, Voc = 1.04 V and FF = 0.73) and a hysteresis index (HI) of 0.048 with a fixed device area of 0.15 cm2 under illumination of AM 1.5G (100 mW cm−2). The significantly improved device performances maybe due to the fact that the carriers more easily be collected for larger grain sizes and fewer grain boundaries by doping 4-MSA into perovskite precursor solution. Furthermore, the sulfonic group is chemically bonded to mp-TiO2 and phenyl backbone has π-conjugated structure, which benefits electron transfer.Download high-res image (328KB)Download full-size image

•CsI as an interface modifier in perovskite solar cell was studied.•The CsI interlayer can improve the quality of perovskite film.•The CsI interlayer can significantly reduce hysteresis of the device.•The CsI-modified device obtains the champion PCE of 17.10%.•The optimal device shows good stability over 60 days under atmospheric humidity.Each interface is crucial to perovskite solar cells (PSCs), so the interface modification is often used to improve the PV performances. In this manuscript, an environment-friendly cesium iodide (CsI) interface layer between the mesoporous TiO2 (mp-TiO2) and the MAPbI3 perovskite active layer was introduced to improve the PV performances and stabilities of PSCs and significantly reduce hysteresis of the device. After optimizing, the PSC employing a CsI-modified mp-TiO2 as electron transporting layer (ETL) could obtain a high fill factor (FF) of 0.79 with an increased power conversion efficiency (PCE) of 17.10% and a low hysteresis index (HI) of 0.10 under illumination of AM 1.5G, while FF of 0.75 and PCE of 14.38% for PSC without CsI interface modification. The enhanced PV performances can be attributed to the improved surface morphology of mp-TiO2, the lower work function (WF) of TiO2, the passivation of surface trap states, the improved perovskite crystallization and reduced grain boundaries. Besides, the reduced WF of TiO2 results in the enhanced built-in potential, which promotes the charge separation, transport and collection.Download high-res image (249KB)Download full-size image

•Two novel dithiafulvenyl-based HTMs are synthesized for efficient PSCs.•Dithiafulvenyl unit has been used to construct HTMs for PSCs for the first time.•PSCs based on the two novel HTMs show higher Voc than Spiro-OMeTAD.•The results reveal the relationship between structure of HTM and performance of PSC.As a promising photovoltaic device, perovskite solar cell (PSC) has gained remarkable attention and shows breathtaking development. In the PSC device, hole transporting material (HTM) is a crucial component to efficiently extract and collect photoinduced charges. In this study, two novel dithiafulvenyl-based small molecules are designed and synthesized as HTMs for PSCs. The only difference of the two HTMs is that replacing phenothiazine in LHTM-1 with carbazole to construct LHTM-2, aiming to study the influences of the minor structural discrepancy on the photovoltaic performance. It shows that the molecular structure change from phenothiazine to carbazole significantly improves the molecular planarity, hole mobility and shifted the highest occupied molecular orbital level downward. Consequently, comparing with LHTM-1, CH3NH3PbI3-based PSC employing carbazole-based LHTM-2 as HTM achieves higher power conversion efficiency (PCE) of 14.81%, which is comparable to Spiro-OMeTAD-based device (PCE = 16.07%). To the best of our knowledge, this is the first time report that dithiafulvenyl-based HTMs for PSCs. These results reveal the fundamental relationships between minor structural discrepancy of HTMs and device performances of PSCs, which will afford significant guide for future development of functional molecules for PSCs.Download high-res image (110KB)Download full-size image

The cracking of electrochromic materials due to aging or reiterative bending is a major problem which noticeably degrades the performance of electrochromic devices. In the present research, we successfully induced a triphenylamine derivative into furfuryl glycidyl ether, and further by a DA cross-linking polymerization reaction with maleimide (MA) to yield polymer DATPFMA. The color of the polymer film could be switched from faint yellow to green grey to dark blue. The observed coloration efficiency values of the polymer for the electrochromic process were 82.2 and 175.3 cm2 C−1 at 580 and 1060 nm, and the coloring and bleaching response times were 4.1 and 11.0 s, respectively. The self-healing process of the polymer film at 110 °C was observed by optical microscopy and the self-healing rate was about 80%. The results indicate that the polymer DATPFMA is a novel electrochromic material with noteworthy self-healing properties.

•Natural cotton thread is used as skeleton to fabricate flexible electrode materials.•Fiber shaped electrode is prepared through a one-step hydrothermal process.•All-solid fiber-shaped supercapacitor achieves good capacitive performance.•The fabric integrated fiber-shaped supercapacitor also shows stable performance.At present, the topic of building high-performance, miniaturized and mechanically flexible energy storage modules which can be directly integrated into textile based wearable electronics is a hotspot in the wearable technology field. In this paper, we reported a highly flexible fiber-shaped electrode fabricated through a one-step convenient hydrothermal process. The prepared graphene hydrogels/multi-walled carbon nanotubes-cotton thread derived from natural cotton thread is electrochemically active and mechanically strong. Fiber-shaped supercapacitor based on the prepared fiber electrodes and polyvinyl alcohol-H3PO4 gel electrolyte exhibits good capacitive performance (97.73 μF cm−1 at scan rate of 2 mV s−1), long cycle life (95.51% capacitance retention after 8000 charge-discharge cycles) and considerable stability (90.75% capacitance retention after 500 continuous bending cycles). Due to its good mechanical and electrochemical properties, the graphene hydrogels/multi-walled carbon nanotubes-cotton thread based all-solid fiber-shaped supercapacitor can be directly knitted into fabrics and maintain its original capacitive performance. Such a low-cost textile thread based versatile energy storage device may hold great potential for future wearable electronics applications.

•The rGO-CT was fabricated via dip-coating and vapour reduction method.•The rGO nanosheets wrapped CT has impressive conductivity.•The rGO nanosheets with implanted CNPs form the 3D hierarchical nanostructures.•The two kinds of FSCs have long cycle life and excellent electrochemical stability.•The FSC based on CNPs/rGO-CT can be knitted into textile while maintaining its initial performance.Fibriform supercapacitors (FSC) are promising energy storage devices for wearable electronics which require excellent durability and fabric-like wearable comfort. In this work, we successfully converted commercial cotton threads (CT) into electrically conductive and electrochemically active threads by introducing reduced graphene oxide (rGO) and carbon nanoparticles (CNPs) using a large-scale producible method (dip-coating combined with low-temperature vapour reduction). The rGO coated CT (rGO-CT) has impressive conductivity which is attributed to the wrapped rGO nanosheets and it is steady enough to tolerate washing process for a long time. After coated with CNPs, the conductivity of CNPs/rGO composites coated CT (CNPs/rGO-CT) has been enhanced tremendously. Meanwhile, the rGO nanosheets with implanted CNPs form the three-dimensional (3D) hierarchical nanostructures which provide abundant ion transmission channels. Furthermore, we have prepared the CNPs/rGO-CT based FSC, which exhibits high volumetric capacitance (3.79 mF cm−3 at 50 mV s−1), well cycling stability (95.23% capacitance retention after 10000 charge-discharge cycles), and excellent electrochemical stability (92.30% capacitance retention after 2000 bending cycles). Especially, the CNPs/rGO-CT based FSC maintains great capacitive performance when it was knitted into textile, thus making it meet the high performance requirements of energy storage devices for knittable and wearable electronics.

•Two novel dithiafulvenyl-phenothiazine (DTF-PTZ) based organic dyes were synthesized.•N719 and DTF-PTZ dyes were used for the fabrication of co-sensitized DSSCs.•The PCEs of DSSCs based on co-sensitization were higher than individual dye.•DSSC based on co-sensitization of N719 and PTZ-2 showed the highest PCE of 8.12%.•The highest PCE of co-sensitization DSSC was 16.50% higher than N719 based device.The introduction of additional electron donor and elongation of π-conjugated bridge represents a feasible strategy to enhance light harvesting in both breadth and intensity of donor-(π conjugated spacer)-acceptor (D-π-A) dyes suitable for dye-sensitized solar cells (DSSCs). Here, two novel metal-free organic dyes, in which dithiafulvenyl unit was introduced into phenothiazine donor as an additional electron donor, cyanoacrylic acid as the electron acceptor, and without (PTZ-2) or with (PTZ-3) a benzene as the π-linker between phenothiazine donor and cyanoacrylic acid electron-withdrawing group, were synthesized by modifying the simple D-π-A dye (PTZ-1) and successfully utilized in DSSCs. Their photophysical, electrochemical, photovoltaic properties and theoretical calculations were further investigated. Relative to the reference dye PTZ-1, the power conversion efficiencies (PCEs) increased significantly from 4.04% to 5.81% (PTZ-2) and 5.22% (PTZ-3), which came mainly from the enhancement of short-circuit current (Jsc) due to the broader molecular absorption spectra and higher molar extinction coefficients. What's more, it is worth noting that the dyes of PTZ-2 and PTZ-3 have strong absorption, which can compensate for that of N719 in the low wavelength region, especially in the region of ∼300–500 nm. Therefore, a co-sensitization approach has been used for achieving enhanced performances in DSSCs wherein N719 was co-sensitized with PTZ-2 and PTZ-3, respectively. Consequently, the co-sensitized DSSC (PTZ–2 + N719) gave the highest efficiency of 8.12%, exhibiting an improvement of 16.50% compared to the device sensitized with N719 alone (PCE = 6.97%) under the same conditions.

•Two simple co-sensitizers were synthesized for N719-based DSSCs.•The co-sensitizers could avoid dye aggregation and reduce charge recombination.•Both Jsc and Voc of the co-sensitized DSSCs were enhanced relative to single N719.•Co-sensitization of a DSSC with N719 and LD04 exhibited the highest PCE of 8.955%.Compared with the development of novel organic dyes, co-sensitization is a much more convenient way to achieve highly efficient dye-sensitized solar cells (DSSCs). Here, two simple donor-(π conjugated spacer)-acceptor dyes, in which hexyloxy-substituted phenyl as an electron donor, cyanoacrylic acid as the electron acceptor and different spacers thiophene (LD03) or furan (LD04) as the π-linkers, were designed and synthesized as co-sensitizers for N719-based DSSCs. The photophysical, electrochemical, photovoltaic performances and electrochemical impedance spectroscopy of these DSSCs were investigated in detail. When compared to the DSSCs fabricated from individual N719, the co-sensitized DSSCs (N719 + LD03 and N719 + LD04) showed significantly enhanced power conversion efficiencies (PCEs), short-circuit photocurrent density (Jsc) and open circuit voltage (Voc) simultaneously, which owing to the co-sensitizers could effectively overcome the competitive light absorption by I3− in the electrolyte, avoid dye aggregation and reduce the charge recombination. Consequently, the co-sensitized DSSC (N719 + LD04) gave the highest PCE of 8.955% (Jsc = 17.628 mA cm−2, Voc = 0.758 V and fill factor = 0.670), exhibiting an improvement of 13.412% compared to the device sensitized with N719 alone (PCE = 7.896%) under illumination (AM 1.5G, 100 mW cm−2).Figure optionsDownload full-size imageDownload as PowerPoint slide

This paper shows a simple approach for the electrodeposition of V2O5 nanoparticles on a TiO2 nanorod arrays substrate by combining hydrothermal and electrochemical deposition methods. The electrochemical and optical properties of the TiO2/V2O5 hybrid film have been investigated and the results show that the hybrid film has obviously better electrochemical and electrochromic properties compared with the single V2O5 thin film. The TiO2/4cir-V2O5 hybrid film shows the most improved electrochromic properties with excellent cyclic stability, outstanding transmittance modulation (50% at 780 nm) and high coloration efficiency (28 C−1 cm2 at 780 nm). The modified electrochromic properties are mainly due to the TiO2 nanorod array structure, which contributes to improve the structural stability of the V2O5 film and benefits the intercalation/deintercalation process of Li+ ions within the V2O5 film.

•Two new PTZ-based organic dyes were synthesized and characterized.•The dyes are studied by DFT and TD-DFT calculations.•The introduction of benzil-based auxiliary donors improves the light-harvesting ability.•The DSSCs based on WY5 and WY6 have higher Jsc than that of T0.•The DSSC based on dye WY6 obtains the highest η of 5.52%.Two new D-D-π-A phenothiazine-based metal free organic dyes (WY5, WY6) were designed, synthesized, and applied in dye-sensitized solar cells (DSSCs) by introducing of benzil-based auxiliary electron donors into simple D-π-A phenothiazine dye to improve the related photovoltaic performances. In the WY6-based solar cell, 4,4′-dimethoxybenzil acts as electron donor was used to improve the electron donating ability. So, the WY6-based solar cell finally obtains a better photovoltaic performance than that of WY5-based one. Furthermore, with the addition of benzil-based auxiliary donor, the absorption properties turn better, which directly results in the enhanced short-circuit photocurrent density (from 8.78 (T0) to 10.58 (WY5) and 11.50 mA cm−2 (WY6)) and thus the enhanced power conversion efficiency (from 4.24 (T0) to 4.78 (WY5) and 5.52% (WY6)). In a word, the addition of benzil-based auxiliary electron donors effectively improved the performances of DSSCs.

•Three novel indole-based organic dyes are synthesized and characterized.•The dyes are studied by DFT calculations.•WY2 with PTZ as electron donor shows the best performance.•The DSSC based on WY2 obtains the conversion efficiency of 3.30%.Three novel organic dyes WY1, WY2 and WY3 with the same π-conjunction linker and acceptor but different donor units were synthesized and characterized to investigate the effects of different electron donor units on their photophysical, electrochemical and photovoltaic properties. Density functional theory calculations were carried out to study the ground state geometry structures and electronic structures of the three dyes. Under standard global AM 1.5 solar condition, the solar cells based on WY1, WY2 and WY3 show the overall power conversion efficiencies as 2.15%, 3.30% and 2.09%, respectively. All the investigation results reveal that different electron donors in organic dyes could cause significant differences in photovoltaic performances and organic dye WY2 with N-hexylphenothiazine as electron donor could show the best performance among the three dyes.

Dye-sensitized solar cells (DSSCs) have attracted significant attention as alternatives to conventional silicon-based solar cells owing to their low-cost production, facile fabrication, excellent stability and high power conversion efficiency (PCE). The dye molecule is one of the key components in DSSCs since it significant influence on the PCE, charge separation, light-harvesting, as well as the device stability. Among various dyes, easily tunable phenothiazine-based dyes hold a large proportion and achieve impressive photovoltaic performances. This class of dyes not only has superiorly non-planar butterfly structure but also possesses excellent electron donating ability and large π conjugated system. This review summarized recent developments in the phenothiazine dyes, including small molecule phenothiazine dyes, polymer phenothiazine dyes and phenothiazine dyes for co-sensitization, especially focused on the developments and design concepts of small molecule phenothiazine dyes, as well as the correlation between molecular structures and the photovoltaic performances.The recent developments of small molecule phenothiazine dyes, polymer phenothiazine dyes and phenothiazine dyes for co-sensitization have been summarized, with an emphasis on the developments and molecular design strategies, as well as the correlation between molecular structures and the photovoltaic performances.

Hierarchical NiS2 hollow microspheres (HM-NiS2) were successfully in situ grown on FTO by a one-step hydrothermal method, and then tested as the counter electrode (CE) for dye-sensitized solar cell (DSSC) for the first time. The SEM images reveal that the hierarchical NiS2 microspheres were successfully grown on FTO substrate. It is worth noting that some of the shells are partially broken, which is advantageous for providing more electrolyte adsorptions and electrocatalytic active sites. The electrocatalytic ability and electrochemical properties of the HM-NiS2 were studied by cyclic voltammetry, electrochemical impedance spectroscopy and Tafel polarization. The power conversion efficiency of 7.84% is achieved for the DSSC based on HM-NiS2 CE, which is close to that of the DSSC using Pt CE (7.89%). The results indicate that the in situ fabricated HM-NiS2 CE may be a good candidate for high efficiency and low-cost DSSCs.

•NiO/V2O5 hybrid electrochromic film has been prepared.•The hybrid film was obtained with nanoflake-like NiO film as substrate.•The hybrid film has a nanoporous structure.•The hybrid film has good electrochromic properties.Nanoporous NiO/V2O5 hybrid film has been successfully prepared by combining chemical bath deposition (CBD) and electrochemical deposition methods. The electrochemical and optical properties of the hybrid film were investigated by cyclic voltammetry (CV), amperometric i–t, UV–vis spectroscopy and colorimetry analysis. Compared with single V2O5 electrochromic film, the NiO/V2O5 hybrid electrochromic film reveals reasonably good cyclic stability, better transmittance modulation (35% at 776 nm) and higher coloration efficiency (30.6 C−1 cm2 at 776 nm). The noticeably improved electrochromic properties are mainly attributed to the introduction of NiO polycrystal substrate with nanoflake-like structure, which helps strengthen the structural stability of V2O5 film and improve the performance of Li+ ions intercalation/deintercalation.

Dithiafulvenyl–triphenylamine (DTF–TPA) based organic dyes with different alkyl chains attached on the DTF unit were examined to investigate the effect of alkyl chain lengths on the photovoltaic performances of dye-sensitized solar cells (DSSCs). Relative to WD9 with two methyl groups, the power conversion efficiency (η) increased significantly from 3.18% to 4.29% (WD12 with two hexyl chains) and 4.62% (WD13 with two decyl chains) in the absence of the chenodeoxycholic acid (CDCA). An increase in η of about 45.2% was obtained from WD9 to WD13. The attached longer alkyl chains in DTF–TPA based organic dyes are effective to suppress the electron recombination and reduce the interactions between dye molecules. Electrochemical impedance spectroscopy studies indicate that both the resistance for charge recombination and the electron lifetime are increased after the increase of alkyl chains length to the dye molecules. The η of DSSC based on WD9 was markedly increased by about 28.6% in the presence of CDCA as compared to that in the absence of CDCA. However, the η of WD13-sensitized DSSC was not dependent on CDCA and decreased by about 5.4% in the presence of CDCA. This work indicates that the incorporation of longer alkyl chains into DTF–TPA organic dyes is a promising way for efficient coadsorbent-free DSSCs.

•Two novel imidazole–triphenylamine-based organic dyes were designed and synthesized.•The DFT and TD-DFT calculations have been used to study the dyes.•The photophysical and photovoltaic properties of the dyes were investigated.•The dye with p-methoxyphenyl group has a better photovoltaic performance.•The DSSC based on CD-4 obtains an overall conversion efficiency of 4.11%.In order to study the influence of different imidazole derivatives in triphenylamine-based organic dyes, two different imidazole derivatives are introduced into the phenyl ring of the triphenylamine core, coded as CD-4 and CD-6, respectively. Their photophysical, electrochemical properties and the performances of the corresponding dye-sensitized solar cells (DSSCs) are further investigated. Due to the better molar extinction coefficient, quantum efficiency (QE) and longer lifetime of excited electron, the DSSC based on CD-4 has the higher overall conversion efficiencies as 4.11% than that of CD-6 as 1.51% under full sunlight (AM 1.5G, 100  mW cm−2) irradiation. Density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations were carried out to study the ground state structures, the electronic structures and the optical properties of the two dyes. The simulated UV–vis absorption spectra for the two dyes are in excellent agreement with the experimental results.

•CD-7-sensitized photoanodes by THF or DMF bath have been prepared.•The results are studied by experimental analyses and computational modeling.•Different solvent baths have different effects on dye aggregation and adsorption.•Different solvent baths have significant influences on IPCE and electron lifetime.•The different photovoltaic properties of the DSSCs have been investigated.Combining experimental analyses and computational modeling, we investigated CD-7-sensitized solar cells (DSSCs) by THF or DMF bath with aim to understand the effects of different solvent baths on the performances of the corresponding DSSCs. In experiment, the photophysical, photovoltaic and electrochemical impedance properties of the DSSCs based on THF or DMF bath were investigated. The UV–vis spectrum of CD-7 in THF is red-shifted in comparison with it in DMF, indicating that there are different interactions between CD-7 and the solvent molecules. The UV–vis spectrum of CD-7 adsorbed on TiO2 film suggested that different solvent baths have different effects on the J-aggregation and absorption strength. Monochromatic incident photon-to-electron conversion efficiency (IPCE) and electrochemical impedance analyses showed that different solvent baths have significant influences on the IPCE values and electron lifetimes of the corresponding DSSCs. The analysis results of computational modeling showed that the solvent molecules would affect the energy level of TiO2, adsorption structure and adsorbed amount of CD-7 on the TiO2 film. The above analysis results illuminate a big difference in the performances of DSSCs by THF or DMF bath. The DSSCs based on THF bath obtained the η value 1.53%, which is about twice as much as that of DMF bath.Graphical abstract

•Polyaniline and TiO2 nanorods array hybrid electrochromic film was obtained.•Electrochromic properties of the hybrid film were studied.•The hybrid film has the loose and porous surface.•The hybrid film could exhibit three different colors.Titanium dioxide (TiO2) nanorods (NRs) array was successfully prepared via hydrothermal method on fluorine doped tinoxide (FTO) coated transparent conductive glass substrate. The hybrid film of polyaniline (PANI)/TiO2 NRs was achieved through electrochemical polymerization of aniline onto the TiO2 NRs array film. The electrochromic and optical properties of the hybrid film were investigated by cyclic voltammetry (CV), amperometric i–t and UV–vis spectroscopy. The results indicate that the hybrid film has long term stability and reversible color changes after cyclic voltammetry scans for 200 circles. The PANI/TiO2 NRs hybrid film can show three different colors. Response time of PANI/TiO2 NRs hybrid film is about 0.7 s and 2.6 s at different states, respectively. The TiO2 NRs array and the loose, porous surface among the hybrid film facilitate charge transmission and also provide large surface area for electrochemical reaction.

•A novel carbazole-triphenylamine-based electrochromic film has been prepared.•The film could exhibit different colors as bluish green, light yellow and off-white.•The film can sensitively change its color within seconds.•The biggest different average emissivity dynamic of the film is 0.082.4,4′-Di(N-carbazolyl)triphenylamine (DCBZ-TPA) is synthesized and its polymer film was deposited on ITO-glass through electrochemical polymerization. Electrochromic properties of the novel film were investigated by cyclic voltammetry and amperometric i–t curve. The optical properties of the film were investigated by UV–vis and FT-IR spectroscopy. The electrochromic film can sensitively change its color within seconds, which can be described as bluish green, light yellow and off-white. A biggest different average emissivity dynamic of the film is 0.082 in the wavelength of 8–14 μm.

•A novel b-PEDOT/MWCNTs/rGO hybrid nanocomposite was prepared.•The nanocomposite as electrode material for supercapacitor was studied.•The nanocomposite could exhibit a specific capacitance of 225 F g−1.•The synergistic effects of rGO, PEDOT and MWCNTs in the nanocomposite were studied.The hybrid nanocomposite based on poly(3,4-ethylenedioxythiophene)/multiwalled carbon nanotubes/graphene was prepared by reducing the graphene oxide with hydrazine in the presence of multiwalled carbon nanotubes (MWCNTs) and the anchored poly(3,4-ethylenedioxythiophene) hollow spheres (b-PEDOT). The transmission electron microscope (TEM) images of b-PEDOT/MWCNTs/rGO nanocomposite reveal that the b-PEDOT and MWCNTs were sandwiched between layers of graphene sheets. The b-PEDOT nanoparticles act as spacers to create gaps between neighboring graphene sheets, resulting in a higher surface area compared to pure graphene. Furthermore, it shows a significant pseudocapacitance energy storage mechanism during the charge/discharge process. And the MWCNTs improve electric conductivity of the nanocomposite and contribute to a low equivalent series resistance (ESR). Utilizing this composite material, a specific capacitance of 225 F g−1 at a current density of 0.1 A g−1 has been achieved.

•Two imidazole-based organic dyes were synthesized and applied in DSSCs.•Effects of different electron acceptors on these organic dyes were studied.•DB-1 with cyanoacetic acid gives effective and faster electron injection.•DB-1 shows the better photovoltaic performance.In this paper, a comparative study on the photophysical, electrochemical properties and photovoltaic performances of simple imidazole-based dyes containing varying electron acceptors is done. Two organic dyes containing 4,5-diphenyl-1H-imidazole (DPIM) unit as electron donor and cyanoacetic acid (for DB-1) or rhodanine-3-acetic acid (for DB-2) as electron acceptor are designed and synthesized. The LUMO and HOMO energy levels of the two dyes can be ensuring positive effect on the process of electron injection and dye regeneration. The overall conversion efficiencies of 1.63% and 0.51% were obtained for DSSCs based on DB-1 and DB-2, respectively. In comparison with DB-1, DB-2 shows the lower JSC, VOC, and efficiency, which is attributed to the lower excited electron injection efficiency and faster charge recombination rate.

•Three novel phenothiazine–triphenylamine-based organic dyes are designed.•The dyes contain different aromatic groups as conjugated spacers.•The dyes before and after binding to TiO2 are studied by DFT and TD-DFT.•The simulated spectra of CD-1∼3 show better absorption than that of WD-8.•The dyes could be used as potential sensitizers for DSSCs.Three phenothiazine–triphenylamine-based organic dyes (CD-1, CD-2 and CD-3) are designed based on the dye WD-8. The geometries, electronic structures, and electronic absorption spectra of these dyes before and after binding to TiO2 are studied by density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The calculated geometries indicate that these dyes show good steric hindrance effect which is advantage to inhibit the close intermolecular π–π aggregation effectively. The lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels of these dyes could ensure positive effect on the process of electron injection and dye regeneration. The simulated spectra of CD-1∼3 show better absorption than that of WD-8 in the low energy zone. All the calculated results demonstrate that these dyes could be used as potential sensitizers for DSSCs and show better performances than WD-8.

A novel electrochromic film based on the copolymer of aniline and o-anisidine was obtained by electrochemical polymerization method. The electrochromic properties of the novel film were investigated by cyclic voltammetry and amperometric i–t curve. The optical properties of the film were investigated by UV–vis spectrophotometer and FT-IR spectroscopy. The results show that different colors of the electrochromic film could be achieved, which exhibits as light grass green, emerald green and blue-violet. The maximum difference of the UV–vis absorption of the film is about 60% between −0.6 V and 1.0 V, respectively. The biggest different average emissivity dynamic of the film is 0.408 in the wavelength of 8–14 μm region.Graphical abstractHighlights► A novel electrochromic film based on the copolymer of aniline and o-anisidine was obtained. ► The electrochromic film could exhibit different colors as light grass green, emerald green and blue-violet. ► The maximum UV–vis absorption difference of the film is about 60%. ► The biggest different average emissivity dynamic of the film is 0.408.

•Two new organic dyes containing different imidazole derivatives have been synthesized.•The imidazole derivative in dye TPA-B5 has the non-planar structure.•Dye TPA-B5 has the higher photovoltaic performance compared to the similar dyes.•The DSSC device based on TPA-B5 achieved the overall conversion efficiency of 3.13%.In order to study the influence of imidazole derivatives in triphenylamine-based organic dyes, two different imidazole derivatives are introduced into the phenyl ring of the triphenylamine core, coded as TPA-B5 and TPA-B6, respectively. The photophysical and electrochemical properties of the dyes are investigated by UV–vis spectroscopy and cyclic voltammetry. TPA-B5 increases the molar extinction coefficients and λmax because of the extension of the π-conjugation structure of the dye and non-planar structure of imidazole derivative. However, TPA-B6 does not increase the molar extinction coefficients and λmax compared with a simple triphenylamine derived dye (TPA-1), which may be due to the planar structure of imidazole derivative and benzene ring. The structure of TPA-B6 is in favor of the formation of dye aggregates on the semiconductor surface and the recombination of conduction band electrons with triiodide in the electrolyte. Overall conversion efficiencies of 3.13% and 1.21% under full sunlight (AM 1.5G, 100 mW cm−2) irradiation are obtained for DSSCs based on the two new dyes, under the same conditions, the dye TPA-1 and di-tetrabutylammonium cis-bis(isothiocyanato) bis(2,2′-bipyridyl-4,4′-dicarboxylato) ruthenium(II) (N719) give overall conversion efficiencies of 2.23% and 5.38%, respectively. Although the overall conversion efficiencies of these dyes are not very high, the results will still afford significant value for future development of efficient D–π–A sensitizers.

In order to increase the electron-donating ability of the donor part of the organic dye, two phenothiazine groups, as additional electron donors, were introduced into a triphenylamine unit to form a starburst donor–donor (2D) structure in this paper. Three new organic dyes (WD-6, WD-7 and WD-8) containing this starburst 2D structure and a 2-cyanoacetic acid acceptor linked by various conjugated linkers (benzene, thiophene, and furan) have been designed, synthesized and applied in dye-sensitized solar cells (DSSCs). The introduction of a phenothiazine group with a butterfly conformation in the triphenylamine donor parts has a good influence on preventing the molecular π–π aggregation due to the starburst 2D structure of the organic dye. The conjugated linker effects on the photophysical, electrochemical and photovoltaic properties of these organic dyes were investigated in detail. The DSSCs made with these organic dyes displayed remarkable overall conversion efficiencies, ranging from 4.90–6.79% under an AM 1.5 solar condition (100 mW cm−2). The best performance was found for organic dye WD-8, in which a furan group was the conjugated linker. It displayed a short-circuit current (Jsc) of 14.43 mA cm−2, an open-circuit voltage (Voc) of 682 mV, and a fill factor (ff) of 0.69, corresponding to an overall conversion efficiency of 6.79%. The different photovoltaic behaviors of the solar cells based on these organic dyes were further elucidated by the electrochemical impedance spectroscopy.

Two new triphenylamine-based starburst dyes (WD-2 and WD-3) are designed, in which the carbazole/phenothiazine groups are used as secondary electron donor and the rhodanine-3-acetic acid moiety as the acceptor. We report the synthesis, photophysical and electrochemical properties of the dyes as well as their applications in dye-sensitized solar cells (DSSCs). Under standard global AM 1.5 solar condition, the WD-2 sensitized cell gives a short circuit photocurrent density Jsc = 6.4 mA cm−2, an open circuit voltage Voc = 600 mV, a fill factor ff = 0.8, corresponding to an overall conversion efficiency of 3.1%. Under the same conditions, the WD-3 sensitized cell gives Jsc = 4.7 mA cm−2, Voc = 570 mV, and ff = 0.78, corresponding to an overall conversion efficiency of 2.1%. The conversion efficiency is increased about 47% from WD-2 sensitized cell to WD-3 sensitized cell. The research results show that the inefficient electron injection from the excited dyes into the conduction band of TiO2 results in the low efficiencies of DSSCs based on the two dyes.Graphical abstractHighlights► The phenothiazine group as secondary electron donor was introduced into organic dyes. ► The dyes with the starburst conformations can reduce aggregation between molecules and avoid the charge recombination processes of injected electrons with triiodide in the electrolyte. ► Power conversion efficiency of 3.1% was obtained for the DSSCs based on WD-2 without deoxycholic acid.

In dye-sensitized solar cells (DSSCs), as the excited electrons from dye molecules are injected to the conduction band of semiconductor film through the acceptor moieties, the acceptor groups have significant influences on the photovoltaic properties of the dyes. In this paper, the effects of different acceptor groups (cyanoacetic acid and rhodanine-3-acetic acid) in two phenothiazine-triphenylamine dyes (PTZ-1 and PTZ-2) on the optical, electrochemical properties and photovoltaic performances were studied. In comparison with PTZ-2, the photovoltaic performance of PTZ-1 is significantly improved by replacing rhodanine-3-acetic acid to cyanoacetic acid. The conversion efficiency of solar cell based on the PTZ-1 is increased about 110%. The lower efficiency of solar cell based on PTZ-2 is mainly because the delocalization of the excited state is broken between the 4-oxo-2-thioxothiazolidine ring and the acetic acid, which affects the electron injection from PTZ-2 to the conduction band of TiO2.Highlights► The phenothiazine-triphenylamine organic dyes with different acceptors were studied. ► The absorption of PTZ-2 with rhodanine-3-acetic acid shows an obvious red shift. ► PTZ-1 gives effective and faster electron injection from the LUMO to TiO2 electrode. ► PTZ-1 with cyanoacetic acid as acceptor shows the better photovoltaic performance.

Three organic sensitizers containing identical π-spacers and electron acceptors but different arylamine electron donors, carbazole, phenothiazine and diphenylamine, were applied in dye-sensitized solar cells to study the influence of the different electron donors on the photophysical, electrochemical and photovoltaic properties by spectral, electrochemical, photovoltaic experiments, and density functional theory calculations. The overall dye-sensitized solar cell conversion efficiencies ranged from 1.77% to 2.03%. Electrochemical impedance spectroscopy results are in good agreement with results of the short-circuit currents and the overall conversion efficiencies of the dye-sensitized solar cells based on the three dyes.Highlights► Three organic dyes with different donors were applied in dye-sensitized solar cells. ► Effects of different electron donors on the photovoltaic performances were studied. ► The dye derived from diphenylamine has the longest maximum absorption with the highest molar absorption coefficient. ► The dye containing the diphenylamine donor gives the better photovoltaic performance. ► The electrochemical impedance spectroscopy results are in good agreement with the photovoltaic performances of the dyes.

A novel π-conjugated donor–acceptor compound (1) based on tetrathiafulvalene (TTF), which is functionalized with dipyridine, has been designed and synthesized. Spectroscopic and electrochemical behaviors of compound 1 demonstrate that the donor (TTF) unit strongly interacts with the electron-accepting group through the heteroaromatic bridge. The interaction of compound 1 with metallic ions can cause remarkable changes in the absorption and fluorescence spectra. DFT calculations reveal that the pyrazine ring is almost coplanar with the TTF plane, which is beneficial to the donor and acceptor electronic communication. Additionally, compound 1 can be self-assembled into nanostructures with smooth surface, hecto-nanometers in width and deca-micrometers in length.Graphical abstractHighlights► Compound 1 has significantly intramolecular charge transfer interaction. ► Compound 1 with metallic ions can cause remarkable changes in the spectra. ► The pyrazine ring in compound 1 is almost coplanar with the TTF plane. ► Compound 1 has been self-assembled into micro/nanostructures.

The synthesis and application to dye-sensitized solar cells of two new triphenylamine-based organic dyes containing benzimidazole derivatives as secondary donors together with a simple triphenylamine derived dye for the purpose of comparison is reported. The photophysical and electrochemical properties of the dyes were investigated by UV–vis spectroscopy and cyclic voltammetry. The introduction of benzimidazole derivatives in the phenyl ring of the triphenylamine core increases the molar extinction coefficients and λmax because of the extension of the π-conjugation structures of the dyes. Overall conversion efficiencies of ∼2.5% under full sunlight (AM 1.5G, 100 mW cm−2) irradiation were obtained for DSSCs based on these new dyes, under the same conditions, the reference dye and di-tetrabutylammonium cis-bis(isothiocyanato) bis(2,2′-bipyridyl-4,4′-dicarboxylato) ruthenium(II) (N719) gave overall conversion efficiencies of 1.23% and 5.61%, respectively. Our findings demonstrate that the introduction of benzimidazole derivatives as secondary donors in triphenylamine-based dye can improve their photovoltaic performance compared to the unsubstituted reference dye in DSSCs.Graphical abstractHighlights► Two new triphenylamine-based organic dyes containing benzimidazole derivatives have been synthesized. ► The introduction of benzimidazole derivatives increases the molar extinction coefficients and λmax of the new dyes. ► The overall conversion efficiencies of 2.43% and 2.65% were obtained based on the new dyes. ► Introduction of benzimidazole derivatives into triphenylamine-based dyes improves their photovoltaic performances.

A novel and highly conjugated donor–acceptor dyad consisting of tetrathiafulvalene unit covalently attached to a porphyrin unit has been synthesized and characterized. As compared to tetraphenylporphyrin, the fluorescence intensity and lifetime of the dyad was decreased owing to photoinduced electron transfer between the tetrathiafulvalene and porphyrin units in the excited state. The fluorescence intensity of the dyad was recovered dramatically upon the addition of Fe(ClO4)3·6H2O to a solution of the dyad, and the fluorescence intensity grows with an increasing amount of Fe(ClO4)3·6H2O. More importantly, the fluorescence intensity of the dyad can be reversibly modulated by the sequential electrochemical oxidation and reduction of the tetrathiafulvalene unit, thus a new redox fluorescence switch based on this dyad has been constructed.Highlights► A novel donor–acceptor dyad has been synthesized and characterized. ► The fluorescence quenching behavior of the dyad has been investigated. ► The fluorescence intensity of the dyad can be reversibly modulated. ► A new redox fluorescence switch based on dyad 1 has been constructed.

A new tetrathiafulvalene (TTF) derivative—5,6-diamino-2-(4,5-bis(decylthio)-1,3-dithio-2-ylidene)benzo[d]-1,3-dithiole (1) with strong amphiphilic character and good reversible redox property has been synthesized. The Langmuir–Blodgett (LB) film of compound 1 was fabricated and its physical properties were characterized by UV–vis spectra, X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM) and surface profiler. The room temperature in-plane dc conductivity of the LB film increases from 10−7 S cm−1 to 10−5 S cm−1 after doped by iodine.Graphical abstractHighlights► A new tetrathiafulvalene (TTF) derivative (1) possessing strong amphiphilic character and good reversible redox property has been synthesized. ► The LB film of compound 1 is fabricated and its physical properties are characterized. ► The room temperature in-plane dc conductivity of the LB film increases from 10−7 S cm−1 to 10−5 S cm−1 after doped by iodine.

Three carbazole–triphenylamine-based dyes (D1, D2, D3) are designed. The geometries, electronic structures, and electronic absorption spectra of these dyes are studied by DFT and TD-DFT. The calculated geometries indicate that these dyes are all noncoplanar, which can help to inhibit the close intermolecular π–π aggregation effectively. The LUMO and HOMO energy levels of these dyes can be ensuring positive effect on the process of electron injection and dye regeneration. The trend of the calculated HOMO–LUMO gaps nicely compares with the spectral data. The calculated results of these dyes demonstrate that these dyes can be used as potential sensitizers for TiO2 nanocrystalline solar cells.Graphical abstractHighlights► Carbazole–triphenylamineb-ased dyes were designed and studied by DFT and TD-DFT. ► The calculated geometries indicate that these dyes are all noncoplanar. ► The trend of the calculated HOMO–LUMO gaps nicely compares with the spectral data. ► These dyes can be used as potential sensitizers for dye-sensitized solar cells.

The properties of two donor–acceptor compounds tetrathiafulvalene-acenaphtho[1,2-b] quinoxaline (1) and tetrathiafulvalene-3-nitro-acenaphtho[1,2-b]quinoxaline (2) have been investigated by solution-state studies (electrochemistry, absorption, self-assembly) and theoretical calculations (DFT, TD-DFT). The electrochemical studies indicate the nitro-substituted effect on their redox properties is negligible. Both compounds show effective intramolecular charge transfer (ICT) transitions in the UV-Visible range in solution. Compared with compound 1, compound 2 has a bathochromic shift in the absorption spectra, the λmax−ICT has been extended from 20800 cm−1 to 19700 cm−1 (480 nm to 507 nm). In addition, when the nitro group is employed, the self-assembly characteristics of the two compounds are substantially changed from ribbon-like nanostructures to root-like nanostructures. Density functional theory (DFT) calculations provide insights into their molecular geometries, electronic structures, and physico-chemical properties.

The poly-O-anisidine (POA) electrochromic film was obtained by cyclic voltammetry method. The optical properties of the electrochromic film were investigated by UV–vis spectrophotometer and FT-IR spectroscopy. The results show that the different colors of the electrochromic film can be achieved, which exhibit as light yellow-green, light dark green and blue. The maximum difference of the UV–vis absorption of the film is about 40% between −0.5 V and 0.9 V and the biggest different average emissivity dynamic of the film is 0.553 in the wavelength of 8–14 μm regions.Graphical abstractHighlights• The POA electrochromic film is obtained by cyclic voltammetry method. • The film can show light yellow-green, light dark green and blue reversibly. • The biggest different average emissivity dynamic of the film is 0.553.

Graphene paper has attracted considerable attention because of its impressive electrical and mechanical properties, which endow it with the great potential for applications in future flexible electronics. Therefore, developing a high-efficiency route to fabricate large-area and foldable graphene paper with good electrical and mechanical properties is quite necessary. In this work, a facile in-situ chemical reduction method for the preparation of graphene paper was successfully developed. The in-situ chemical reduction process involves simultaneous film formation and reduction, and the produced graphene paper has high integrity and good foldability. The thickness and area of graphene paper can also be readily regulated by adjusting the experimental parameters. Furthermore, the dissipation of reductant air stream (HI/CH3COOH air stream) can “push up” the graphene nanosheets to form a loose layered structure. This inside-out reduction process gives the produced graphene paper a sheet resistance as low as 17.8 Ω sq−1, verifying the advantages of this in-situ chemical reduction method. For the application of the obtained graphene paper, a flexible solid-state supercapacitor based on the graphene paper was fabricated, which had a device areal capacitance of 44 mF cm−2 (device volumetric capacitance of 858 mF cm−3) and excellent electrochemical stability.

•Dissolution-recrystallization method can improve perovskite crystallization.•Dissolution-recrystallization method can improve TiO2/perovskite interface.•The optimal perovskite solar cell obtains the champion PCE of 16.76%.•The optimal devices are of high reproducibility.In this work, a dissolution-recrystallization method (DRM) with chlorobenzene and dimethylsulfoxide treating the perovskite films during the spin-coating process is reported. This is the first time that DRM is used to control perovskite crystallization and improve the device performance. Furthermore, the DRM is good for reducing defects and grain boundaries, improving perovskite crystallization and even improving TiO2/perovskite interface. By optimizing, the DRM2-treated perovskite solar cell (PSC) obtains the best photoelectric conversion efficiency (PCE) of 16.76% under AM 1.5 G illumination (100 mW cm−2) with enhanced Jsc and Voc compared to CB-treated PSC.

In order to increase the electron-donating ability of the donor part of the organic dye, two phenothiazine groups, as additional electron donors, were introduced into a triphenylamine unit to form a starburst donor–donor (2D) structure in this paper. Three new organic dyes (WD-6, WD-7 and WD-8) containing this starburst 2D structure and a 2-cyanoacetic acid acceptor linked by various conjugated linkers (benzene, thiophene, and furan) have been designed, synthesized and applied in dye-sensitized solar cells (DSSCs). The introduction of a phenothiazine group with a butterfly conformation in the triphenylamine donor parts has a good influence on preventing the molecular π–π aggregation due to the starburst 2D structure of the organic dye. The conjugated linker effects on the photophysical, electrochemical and photovoltaic properties of these organic dyes were investigated in detail. The DSSCs made with these organic dyes displayed remarkable overall conversion efficiencies, ranging from 4.90–6.79% under an AM 1.5 solar condition (100 mW cm−2). The best performance was found for organic dye WD-8, in which a furan group was the conjugated linker. It displayed a short-circuit current (Jsc) of 14.43 mA cm−2, an open-circuit voltage (Voc) of 682 mV, and a fill factor (ff) of 0.69, corresponding to an overall conversion efficiency of 6.79%. The different photovoltaic behaviors of the solar cells based on these organic dyes were further elucidated by the electrochemical impedance spectroscopy.