Tin-based perovskite solar cells: Further improve the performance of the electron transport layer-free structure by device simulation

•ETL (Electron Transport Layer) is not a prerequisite for excellent device efficiency.•Comprehensive analysis of the factors of solar cells with ETL-free structure.•Excessive thickness of the absorbing layer will lead to an increase in harmful recombination.•Defect density increases the recombination rate and reduces the performance of the device.•Excessive interfacial defect density leads to asymmetric effects.•The lower the valence band of different HTLs, the higher the open-circuit voltage VOC. With the rapid development of perovskite solar cells (PSCs), PSCs without electron transport layer (ETL) structure have been reported one after another, but the efficiency is low. In this work, a tin-based ETL-free structure of perovskite solar cell is introduced. In order to explore the internal influencing factors of the device with ETL-free structure, we used SCAPS-1D (Solar Cells Capacitance Simulator) to simulate the device and adjust the appropriate physical parameters to approximate the results reported in the experiment. The simulation results show that the thickness of the absorption layer, defect density, operating temperature and band gap have different effects on the performance of the device, and the best absorbent layer thickness is 600 nm. When the operating temperature exceeds 300 K, the performance parameters will decrease, and the band gap is best controlled at about 1.3 V. It should be pointed out that defect density is the main culprit that seriously affects device performance. When defect density exceeds 1015cm−3, power conversion efficiency (PCE) begins to decline significantly, and we need to pay more attention to defect density. At the same time, the effects of different interface defect layers (IDL) on device performance are simulated. It is found that when the defect density of the interface defect layer is too high, the asymmetry effect will appear. The interface defect layer IDL2 between the absorption layer and the hole transport layer (HTL) has a greater effect on the open circuit voltage (VOC), and the interface defect layer IDL1 has a greater effect on PCE. Therefore, it is necessary to pay attention to these defect layers to improve the VOC and PCE. Finally, based on ETL-free PSCs, we list HTL of different materials for reference, and provide new ideas for perovskite solar cells in the future.