Numerical simulation and optimization of all-inorganic Ca3PI3/CsSnI3 heterojunction perovskite solar cells

Abstract

To date, inorganic lead-free perovskite solar cells (PSCs) have lagged behind their lead-based and organic–inorganic hybrid counterparts in power conversion efficiency (PCE). To address this challenge, specially avoiding lead toxicity and reducing fabrication costs, we propose a fully inorganic, hole-transport-layer-free (HTL-free) Ca3PI3/CsSnI3 heterojunction device. The device, with FTO/SnS2/Ca3PI3/CsSnI3/Ni structure, is systematically simulated and optimized using SCAPS-1D. The structure featuring a thinner absorber layer at the top and a thicker one at the bottom enhances light utilization efficiency. Further analysis of the energy band diagram and recombination rate distribution reveals that the p/p+-type heterojunction forms a stepwise energy band alignment at the interface, thereby markedly improving the separation efficiency and interfacial transport of photogenerated carriers. Additionally, the influence of defect density (Nt) of both absorber layers and interface layers is also discussed, with defects at the Ca3PI3/CsSnI3 heterojunction more detrimental to performance than those at the SnS2/Ca3PI3 interface. Through multi-parameter collaborative optimization, the device achieves an upper-bound theoretical estimate PCE of 31.27%. This study provides novel insights for developing environmentally sustainable, structurally streamlined, and high-performance heterojunction PSCs.