Study by Numerical Simulation of the Effect of Instability-Induced Defects by Illumination, Thermal, and Bias Stresses in Perovskite Solar Cells and Approaches to Reduce Their Degradation Degree

This study addresses the stability issues affecting TiO₂-MAPbI₂-spiro-OMeTAD (n-i-p type) perovskite solar cells, with a focus on degradation mechanisms induced by various environmental stress factors such as illumination, thermal stress, and bias. Using SCAPS-1D simulation software, we systematically investigate the impact of defects at critical locations within the solar cell structure, including the electron transport layer (ETL)/perovskite interface, the bulk perovskite layer, and the hole transport layer (HTL)/perovskite interface. Four types of defects were analyzed: recombination centers (N_R), shallow donors (N_DT), deep donors (N_DP), and shallow acceptors (N_AT). The simulation results reveal that deep donor defects in the bulk layer (with a concentration of 10¹⁶ cm⁻³) have the most severe impact on device performance, reducing the power conversion efficiency (PCE) from 22.64% to 2.43%, likely due to thermal degradation. Similarly, defects at the ETL/perovskite interface, with a density of 10¹⁴ cm⁻², cause a PCE drop to 16.60%, which can be attributed to light-induced degradation. At the perovskite/HTL interface, defects result in a more moderate decline in PCE to 19.47%, potentially linked to hysteresis effects caused by bias stress. To mitigate these stability challenges, we propose two strategies: the incorporation of PbS buffer layers at both interfaces (ETL/perovskite and HTL/perovskite), and the introduction of a graded perovskite layer that includes MAPbSn_0.1Cl₃ at the rear. These approaches significantly improve the PCE, reducing the degradation effects related to interface and bulk defects. Our findings underscore the critical role of defect management in enhancing the long-term performance of perovskite solar cells.