Hole-Transport Layer-Free Tin-Based Perovskite Solar Cells: Improving Their Performance from a Simulation Perspective

Perovskite solar cells are in rapid development, however, PCE (photovoltaic conversion efficiency) of HTL-free (Hole Transport Layer free) perovskite solar cells is reported to be low. In this work, we propose a tin-based perovskite solar cell with an ETL (Electron Transport Layer) structure of Zn({O}_0.3,{S}_0.7), a novel electron transport layer material. We simulated the device with SCAPS-1D (Solar Cells Capacitance Simulator) and found that all of the absorber layer thickness, band gap, doping concentration, defect density, device working temperature, ETL layer thickness, and doping concentration have different degrees of influence on the device performance. After optimization, {V}_OC (Open Circuit Voltage) is 1.07 V, {J}_SC (Short-circuit Current Density) is 24.25 mA {cm}⁻², FF (Filling Factor) is 87.87%, and PCE arrives up to 22.72%. There is a significant performance improvement compared to pre-simulation (initially, {V}_OC is 0.97 V, {J}_SC is 24.21 mA {cm}⁻², FF is 69.12%, and PCE is 16.22%). It is shown that when the thickness of the absorber layer is larger than the diffusion length, it leads to harmful photogenerated carrier complexes and increases the diffusion length before reaching the electrode, which affects the carrier transport migration. Defect density bears the brunt of the performance impact, the greater it is the worse the performance, so it should be controlled to a small range. When the operating temperature higher than 300 K, the device performance tends to deteriorate and it is recommended to keep the operating temperature around 300 K. The ETL layer doping concentration and thickness have little influence on performance. Finally, we also analytically simulate and compare several traditional ETL PSCs, and the matching of LUMO (Lowest Unoccupied Molecular Orbital) and absorber energy levels of different ETL materials was found to be different, and the higher the matching is, the more favorable the electron transport and the higher the PCE. This work provides new strategy to design PSCs.