Fundamental Flaw in the Current Construction of the TiO2 Electron Transport Layer of Perovskite Solar Cells and Its Elimination

High-Quality TiO2 Electron Transport Film Prepared via Vacuum Ultraviolet Illumination for MAPbI3 Perovskite Solar Cells

The electron transport layer (ETL) plays an important role in determining the conversion efficiency and stability of perovskite solar cells (PSCs). Here, TiO2 thin film was prepared by irradiating diisopropoxy diacetylacetone titanium precursor thin film with 172 nm vacuum ultraviolet (VUV) at a low temperature. The prepared TiO2 thin film has higher electron mobility and conductivity. As it is used as an ETL for MAPbI3 PSCs, its band structure is better matched with the perovskite, and at the same time, due to the good interface contact, more uniform perovskite crystals are formed. Most importantly, a large number of hydroxyl radicals were formed during VUV irradiation of the precursor film, which made up for the oxygen defect present on the surface of the TiO2 thin film, and were adsorbed to the film surface. These hydroxyl groups form hydrogen bonds with methylammonium (MA) components on the MAPbI3 buried surface, thus promoting the transfer of photogenerated electrons at the MAPbI3/ETL interface. The power conversion efficiency of PSCs fabricated in air with the ETL prepared by VUV irradiation is 20.46%, which is higher than that of the contrast solar cell based on the sintered ETL (17.96%).

Numerical Simulation and Optimization of Highly Stable and Efficient Lead-Free Perovskite FA1-xCsxSnI3-Based Solar Cells Using SCAPS

Formamidinium tin iodide (FASnI3)-based perovskite solar cells (PSCs) have achieved significant progress in the past several years. However, these devices still suffer from low power conversion efficiency (PCE=6%) and poor stability. Recently, Cesium (Cs)-doped Formamidinium tin iodide (FA1−xCsxSnI3) showed enhanced air, thermal, and illumination stability of PSCs. Hence, in this work, FA1−xCsxSnI3 PSCs have been rigorously studied and compared to pure FASnI3 PSCs using a solar cell capacitance simulator (SCAPS) for the first time. The aim was to replace the conventional electron transport layer (ETL) TiO2 that reduces PSC stability under solar irradiation. Therefore, FA1−xCsxSnI3 PSCs with different Cs contents were analyzed with TiO2 and stable ZnOS as the ETLs. Perovskite light absorber parameters including Cs content, defect density, doping concentration and thickness, and the defect density at the interface were tuned to optimize the photovoltaic performance of the PSCs. The simulation results showed that the device efficiency was strongly governed by the ETL material, Cs content in the perovskite and its defect density. All the simulated devices with ZnOS ETL exhibited PCEs exceeding 20% when the defect density of the absorber layer was below 1015 cm−3, and deteriorated drastically at higher values. The optimized structure with FA75Cs25SnI3 as light absorber and ZnOS as ETL showed the highest PCE of 22% with an open circuit voltage Voc of 0.89 V, short-circuit current density Jsc of 31.4 mA·cm−2, and fill factor FF of 78.7%. Our results obtained from the first numerical simulation on Cs-doped FASnI3 could greatly increase its potential for practical production.