Since the report of perovskite solar cells in 2009, after more than ten years of development, the photovoltaic conversion efficiency has increased from the initial 3.8% to 25.7%. Perovskite solar cells mainly have planar and mesoporous structures. Compared with planar structure, perovskite solar cells with mesoporous structure have more mesoporous layer. With mesoporous layer, the contact area between the perovskite layer and the electron transport layer can be increased, which accelerates the extraction and transport of electrons, thus reducing the hysteresis effect of the cells. In this study, SnO₂ mesoporous layer was prepared by using hydrothermal method and applied as the electron transport layer of perovskite solar cells. The effects of hydrothermal reaction time on performances of the mesoporous SnO₂ electron transport layer and the perovskite solar cells were evaluated. Composition, morphology, optical and optoelectronic properties of the samples were studied by using XPS, SEM, UV-Vis, J-V and IPCE. It is found that diameter of the SnO₂ nanosheets was increased from 80 nm to 270 nm and the thickness of the mesoporous SnO₂ layer was increased from 70 nm to 350 nm, when the hydrothermal reaction time was prolonged from 3 h to 9 h. When the hydrothermal reaction time was 7 h, photoelectric performance of the device was optimized, with photoelectric conversion efficiency of 14.53%, open-circuit voltage of 1.04 V, short-circuit current density of 19.29 mA·cm⁻² and fill factor of 72.57%.

SnO₂ has been widely used as an electron transport material in perovskite solar cells (PSCs), due to its high optical transmittance and high electron mobility. However, SnO₂ films prepared by using sol-gel method have poor crystallinity owing to the low preparation temperature. There are many defects in the films, which led to the recombination of the photoelectrons, thus reducing the photoelectric conversion efficiency (PCE). The SnO₂ electron transport layers (ETLs) were treated with deionized water, methanol, ethanol and isopropanol. The effects of solvothermal treatments on performance of SnO₂ ETLs and PSCs were studied. With XRD, SEM, contact angle, AFM, UV-Vis, J-V curves and IPCE, physical phase, morphology, roughness, optical performance and photoelectric performance of the samples were characterized. It is found that hydrothermal and solvothermal treatment can increase crystallinity of SnO₂ and visible transmittance of the films, thus enhancing the interfacial contact between ETLs and the perovskite layers. As a result, PCE of the PSCs were effectively improved. Photoelectric performance of the PSCs assembled with the hydrothermally treated SnO₂ was optimized, with the PCE of the cell to be 15.48%, which is 13.8% higher than the PCE (13.60%) of the untreated cell. In addition, the open-circuit voltage (V_oc) was 1.09 V, the short-circuit current density (J_sc) was 19.32 mA·cm⁻², and the fill factor (FF) was 73.18%.

Perovskite solar cells (PSCs) have been developed at a rapid rate. In just over a decade, the photoelectric conversion efficiency (PCE) of PSCs is comparable with that of crystalline silicon solar cells that are developed over 60 years. The two major research topics of PSCs are the improvements of both PCE and stability. Ionic liquids (ILs) have the characteristics of low saturated vapor pressure, high ionic conductivity and low toxicity, which could find applications in the preparation of high-performance PSCs. The application and mechanism of ILs in PSCs as additive or solvent of perovskite materials and as charge transfer layer or modification layer will be reviewed, while the development trend of ILs in PSCs is prospected.

Metal-organic frameworks (MOFs) have received much attention in the field of electrochemistry owing to their high specific surface area, adjustable aperture and tunable structure. A typical V-MOF was synthesized by using hydrothermal methods, where the effects of hydrothermal time on crystalline phase composition and microstructure of V-MOF and its performance for aqueous zinc-ion batteries (AZIBs) were explored. The resulting V-MOF material, a hollow nanorod with a valence of +4 for V after hydrothermal reaction for 36 h, has the highest electrochemical performance as an anode for AZIBs, with a specific capacity of 144.5 mAh·g⁻¹ at a current density of 100 mA·g⁻¹. At a current density of 1000 mA·g⁻¹, the Coulomb efficiency remained at 100% after 4000 charge/discharge cycles.