An amino-functionalized copolymer with a conjugated backbone composed of fluorene, naphthalene diimide, and thiophene spacers (PFN-2TNDI) is introduced as an alternative electron transport layer (ETL) to replace the commonly used [6,6]-Phenyl-C61-butyric acid methyl ester (PCBM) in the p–i–n planar-heterojunction organometal trihalide perovskite solar cells. A combination of characterizations including photoluminescence (PL), time-resolved PL decay, Kelvin probe measurement, and impedance spectroscopy is used to study the interfacial effects induced by the new ETL. It is found that the amines on the polymer side chains not only can passivate the surface traps of perovskite to improve the electron extraction properties, they also can reduce the work function of the metal cathode by forming desired interfacial dipoles. With these dual functionalities, the resulted solar cells outperform those based on PCBM with power conversion efficiency (PCE) increased from 12.9% to 16.7% based on PFN-2TNDI. In addition to the performance enhancement, it is also found that a wide range of thicknesses of the new ETL can be applied to produce high PCE devices owing to the good electron transport property of the polymer, which offers a better processing window for potential fabrication of perovskite solar cells using large-area coating method.

This work reports on incorporation of spectrally tuned gold/silica (Au/SiO₂) core/shell nanospheres and nanorods into the inverted perovskite solar cells (PVSC). The band gap of hybrid lead halide iodide (CH₃NH₃PbI₃) can be gradually increased by replacing iodide with increasing amounts of bromide, which can not only offer an appreciate solar radiation window for the surface plasmon resonance effect utilization, but also potentially result in a large open circuit voltage. The introduction of localized surface plasmons in CH₃NH₃PbI_2.85Br_0.15-based photovoltaic system, which occur in response to electromagnetic radiation, has shown dramatic enhancement of exciton dissociation. The synchronized improvement in photovoltage and photocurrent leads to an inverted CH₃NH₃PbI_2.85Br_0.15 planar PVSC device with power conversion efficiency of 13.7%. The spectral response characterization, time resolved photoluminescence, and transient photovoltage decay measurements highlight the efficient and simple method for perovskite devices.

We report a new concept for the design of metal-free organic dyes (OD5–OD9) with an extended donor–π–acceptor (D–π–A) molecular framework, in which the donor terminal unit is attached by a hole-extending side chain to retard back electron transfer and charge recombination; the π-bridge component contains varied thiophene-based substituents to enhance the light-harvesting ability of the device. The best dye (OD9) has a D–A–π–A configuration with the hexyloxyphenylthiophene (HPT) side chain as a hole-extension component and a benzothiadiazole (BTD) internal acceptor as a π-extension component. The co-sensitization of OD9 with the new porphyrin dye LW24 enhanced the light-harvesting ability to 800 nm; thus, a power conversion efficiency 5.5 % was achieved. Photoinduced absorption (PIA) and transient absorption spectral (TAS) techniques were applied to account for the observed trend of the open-circuit voltage (V_OC) of the devices. This work provides insights into the molecular design, photovoltaic performance, and kinetics of charge recombination.

Supercapacitors based on freestanding and flexible electrodes that can be fabricated with bacterial cellulose (BC), multiwalled carbon nanotubes (MWCNTs), and polyaniline (PANI) are reported. Due to the porous structure and electrolyte absorption properties of the BC paper, the flexible BC-MWCNTs-PANI hybrid electrode exhibits appreciable specific capacitance (656 F g⁻¹ at a discharge current density of 1 A g⁻¹) and remarkable cycling stability with capacitance degradation less than 0.5% after 1000 charge–discharge cycles at a current density of 10 A g⁻¹. The facile and low-cost of this binder-free paper electrode may have great potential in development of flexible energy-storage devices.

Ionic liquid electrolytes are prepared using sulfolane as a plasticizer for eutectic melts to realize highly stable and efficiently performing dye-sensitized solar cells (DSCs) in hot climate conditions. Variations in the viscosity of the formulations with sulfolane content are measured and performance in DSCs is investigated using the ruthenium dye C106 as a sensitizer. A power conversion efficiency (PCE) of 8.2% is achieved under standard reporting conditions. Apart from lowering the viscosity, the addition of sulfolane induces a negative shift of the TiO₂ conduction band edge. Strikingly the device performance increases to 8.4% at 50 °C due to higher short circuit photocurrent and fill factor, over-compensating the loss in open circuit voltage with increasing temperature. The PCE increases also upon decreasing the light intensity of the solar simulator, reaching up to 9% at 50 mW cm⁻². Devices based on these new electrolyte formulations show excellent stability during light soaking for 2320 h under full sunlight at 60 °C and also during a 1065 h long heat stress at 80 °C in the dark. A detailed investigation provides important information about the factors affecting the principal photovoltaic parameters during the aging process and the first results from a series of outdoor measurements are reported.

Sensitizers are responsible for the light harvesting and the charge injection in dye-sensitized solar cells (DSSCs). A fast dye-regeneration process is necessary to obtain highly efficient DSSC devices. Herein, dye-regeneration rates of two DSSC device types, that is, the reduction of immediately formed photo-oxidized sensitizers (ruthenium complex C106TBA and porphyrin LD14, k_ox′) by iodide ions (I⁻) and [Co(bpy)₃]²⁺, and the oxidation of formed photo-reduced sensitizers (organic dye P1, k_re′) by triiodide ions (I₃⁻) and the disulfide dimer (T₂) are investigated by scanning electrochemical microscopy (SECM). We provide a thorough experimental verification of the feedback mode to compare the kinetics for dye-regeneration by using the above mentioned mediators. The charge recombination at the dye/semiconductor/electrolyte interface is further investigated by SECM. A theoretical model is applied to interpret the current response at the tip under short-circuit conditions, providing important information on factors that govern the dynamics of dye-regeneration onto the dye-sensitized heterojunction.

This work reports on an investigation into interfacial charge transfer in CH₃NH₃PbI₃ perovskite solar cells by using anatase TiO₂ nanocuboids enclosed by active {100} and {001} facets. The devices show 6.0 and 8.0 % power conversion efficiency with and without hole-transport material. Transient photovoltage/photocurrent decay and charge extraction, as well as impedance spectroscopy measurements, reveal that carbon materials are effective counter electrodes in perovskite solar cells. The photogenerated charges are observed to be stored in mesoporous TiO₂ film under illumination and in the CH₃NH₃PbI₃ layer in the dark. The use of 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spirobifluorene (spiro-MeOTAD) as a hole-transport material accelerates interfacial charge recombination between the photogenerated electrons and holes.

Herein, we present ultrasmall delafossite-type Mg-doped CuCrO₂ nanocrystals prepared by using hydrothermal synthesis and their first application as photocathodes in efficient p-type dye-sensitized solar cells. The short-circuit current density (J_sc) is notably increased by approximately 27 % owing to the decreased crystallite size and the enhanced optical transmittance associated with Mg doping of the CuCrO₂ nanocrystalline sample. An open-circuit voltage (V_oc) of 201 mV, J_sc of 1.51 mA cm⁻², fill factor of 0.449, and overall photoconversion efficiency of 0.132 % have been achieved with the CuCr_0.9Mg_0.1O₂ dye photocathode sensitized with the P1 dye under optimized conditions. This efficiency is nearly three times higher than that of the NiO-based reference device, which is attributed to the largely improved V_oc and J_sc. The augmentation of V_oc and J_sc can be attributed to the lower valance band position and the faster hole diffusion coefficient of CuCr_0.9Mg_0.1O₂ compared to those of the NiO reference, respectively, which leads to a higher hole collection efficiency.

ZnO nanoparticles are doped with K and applied in p-type dye-sensitized solar cells (DSCs). The microstructure and dynamics of hole transportation and recombination are investigated. The morphology of the K-doped ZnO nanoparticles shows a homogeneous distribution with sizes in the range 30–40 nm. When applied in p-type DSCs in combination with C343 as sensitizer, the K-doped ZnO nanoparticles achieve a photovoltaic power conversion efficiency of 0.012 % at full-intensity sunlight. A further study on the device by transient photovoltage/photocurrent decay measurements shows that the K-doped ZnO nanoparticles have an appreciable hole diffusion coefficient (ca. 10⁻⁶ cm² s⁻¹). Compared to the widely used p-type NiO nanoparticles, this advantage is crucial for further improving the efficiency of p-type DSCs.