Tailoring the Hole Transport Layer and Understanding the Impact of Sn Oxidation for Different Mixed Halide Perovskite Active Layers: On a Quest for the Perfect Match

This research work aimed to identify the optimal parameters of the hole transport layer (HTL) for enhancing the power conversion efficiency (PCE) of mixed halide (FASnI(3))(1-x)(MAPbI(3))(x)-based perovskite solar cells (PSCs). The study analyzed the impact of the HTL properties, such as bandgap (E-g), affinity (mu), mobility (mu(p)), and acceptor-doping density (N-A), on the photovoltaic (PV) parameters of five different PSCs with x = 0, 0.2, 0.4, 0.6, and 1.0. The study revealed that the influence of chi on open-circuit voltage (V-OC) decreases for the HTL with E-g >= 2.95 eV, and higher E-g results in higher V-OC values. The study also found that the impact of mu(p) on short-circuit current density (J(SC)) becomes negligible if mu(p) is more than 2 x 10(-4) cm(2) V-1 s(-1), while the influence of N-A is negligible for N-A of more than 1.5 x 10(17) cm(-3). Moreover, the impact of mu(p) is negligible on V-OC of the cells at the entire N-A range, while with an increase in N-A, V-OC of the cells increases significantly. The study found that the most suitable active layer was with x = 0.2, i.e., (FASnI(3))(0.8)(MAPbI(3))(0.2), which delivered the highest PCE of 23.05%. The oxidation of Sn2+ to Sn4+ can lead to inherent acceptor doping in the absorber layer, which affects device performance. Therefore, this study also investigated the impact of Sn oxidation on the performance of PSCs with Sn-based absorber layers and found that V-OC and fill factor (FF) reduce monotonically as the acceptor doping increases. The reduction in efficiency as a result of Sn oxidation is significant, reducing PCE from 23.05 to 20.86% for the champion device with x = 0.2. The findings of this study contribute to advancing the understanding of mixed halide (FASnI(3))(1-x)(MAPbI(3))(x) PSCs and improving their performance by selecting the appropriate HTL for specific active layers.