Perovskite solar cells (PSCs) have become a promising photovoltaic (PV) technology, where the evolution of the electron‐selective layers (ESLs), an integral part of any PV device, has played a distinctive role to their progress. To date, the mesoporous titanium dioxide (TiO2)/compact TiO2 stack has been among the most used ESLs in state‐of‐the‐art PSCs. However, this material requires high‐temperature sintering and may induce hysteresis under operational conditions, raising concerns about its use toward commercialization. Recently, tin oxide (SnO2) has emerged as an attractive alternative ESL, thanks to its wide bandgap, high optical transmission, high carrier mobility, suitable band alignment with perovskites, and decent chemical stability. Additionally, its low‐temperature processability enables compatibility with temperature‐sensitive substrates, and thus flexible devices and tandem solar cells. Here, the notable developments of SnO2 as a perovskite‐relevant ESL are reviewed with emphasis placed on the various fabrication methods and interfacial passivation routes toward champion solar cells with high stability. Further, a techno‐economic analysis of SnO2 materials for large‐scale deployment, together with a processing‐toxicology assessment, is presented. Finally, a perspective on how SnO2 materials can be instrumental in successful large‐scale module and perovskite‐based tandem solar cell manufacturing is provided.
We presented the results of optical and electrical studies of the properties of hydrogenated amorphous silicon (a-Si:H) film which was prepared by hot wire method. Using transmittance measurements, the dielectric constant of the a-Si:H was determined. The temperature-dependent conductivity was measured using the two-point probe method in the temperature range 115–326 K. It was shown that the temperature-dependent conductivity can be well explained by the nearest-neighbor hopping conduction and the Efros–Shklovskii variable-range hopping conduction models. A clear transition from the nearest-neighbor hopping conduction mechanism to the Efros–Shklovskii variable-range hopping conduction mechanism was also observed. The transition between two conduction regimes and characteristic hopping temperatures, as well as the complete set of parameters describing the properties of the localized electrons (the localization length, the hopping energy, the hopping distance, the width of the Coulomb gap, and the value of the density of states at the Fermi level) were determined.
Undoped and Fe-doped TiO2 thin films were obtained by rf-sputtering technique onto heated glass substrates (250 °C) covered with indium tin oxide. The temperature dependence of the electrical conductivity was investigated in the temperature range 13–320 K, and it shows that the conduction mechanism in the studied samples is described by small-polaron hopping (SPH) at temperatures higher than half of the Debye temperature (θD). It was found that the magnitude of the SPH coupling increases by Fe doping in TiO2 thin films. With decreasing temperature, the conduction behavior transited from SPH conduction to variable-range hopping (VRH) conduction. In the intermediate temperature domain (200 K<T<θD/2), the VRH conduction was found to be dominant, while a temperature-independent conductivity behavior was observed in the lower temperature range (T<200 K).
We carried out the temperature (22–350 K) and magnetic field (0.05 and 1.4 T) dependent Hall mobility and carrier density measurements on Al0.22Ga0.78N/GaN heterostructures with AlN interlayer grown by metal-organic chemical-vapor deposition. Hall data is analyzed with a simple parallel conduction extraction method and temperature dependent mobility and carrier densities of the bulk and two-dimensional (2D) electrons are extracted successfully. The results for the bulk carriers are discussed using a theoretical model that includes the most important scattering mechanisms that contribute to the mobility. In order to investigate the mobility of two-dimensional electron gas, we used a theoretical model that takes into account the polar optical phonon scattering, acoustic phonon scattering, background impurity scattering, and interface roughness scattering in 2D. In these calculations, the values are used for the deformation potential and ionized impurity density values were obtained from the bulk scattering analysis. Therefore, the number of fitting parameters was reduced from four to two.
Summary
Natural dyes extracted from fruits, vegetables, flowers, and leaves are considered as promising alternative sensitizers to replace synthetic dyes for dye‐sensitized solar cells (DSSCs). Generally, solar activity of natural dyes stem from anthocyanin pigment. Carbonyl, carboxyl, and hydroxyl groups present in the anthocyanin molecule improve the adsorption ability of dye on TiO2 and therefore facilitate charge transfer. Here, for the first time, novel natural dyes extracted from St. Lucie cherry, yellow jasmine, and madder berries are reported to act as sensitizer in DSSCs. These novel natural dye extracts are prepared by dissolving related fruits in ethanol. The ingredient of the dyes is identified by FT‐IR spectroscopy. Accordingly, FT‐IR spectrum reveals that novel natural dye extracts exhibit all the characteristic peaks of anthocyanin pigment. Specifically, St. Lucie cherry consists of more distinct carbonyl group than other sources. Also, photoanodes composed of three TiO2 layers are prepared by using a spin‐coating method. Then, they are immersed into natural dyes and analyzed by conducting UV‐Vis spectroscopy. Compared with bare TiO2, natural dye–loaded photoanodes demonstrate far higher absorption ability in the visible region. After fabrication of devices with different novel natural dye sensitizers, current‐voltage characteristics and electrochemical impedance spectroscopy measurements are performed. The best power conversion efficiency (PCE) of 0.19% is obtained by sensitization of St. Lucie cherry with an open‐circuit voltage (Voc) of 0.56 V, short‐circuit current density (Jsc) of 181 μA cm−2, and fill factor (FF) of 0.55. Furthermore, St. Lucie cherry–sensitized devices show the lowest charge transfer and highest recombination resistances. This result can be attributed to the obvious carbonyl group exhibited by St. Lucie cherry.
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