Photovoltaic Performance Study of Cs₂SnI₆-Based Perovskite Solar Cells with Gradient Structures: First-Principles Calculations and SCAPS Analysis

Cs2SnI6 is an ecologically friendly and air stable alternative to lead halide perovskite solar cells (PSCs) for photovoltaic applications. PSCs based on Cs2SnI6 have gained popularity due to their inexpensive cost and simple construction, which eliminates the hole transport layer (HTL). Yet, PSCs without HTL continue to perform worse than PSCs with HTL. We propose a gradient structure doping approach for the Cs2SnI6 PSC and investigate its potential efficiency using first-principles calculations (DFT) and SCAPS-1D in this work. DFT calculation begins by being utilized to analyze the absorption layer's structure and optoelectronic properties (density of states, optical properties, band structure). The effects of varied defect density, doping gradients, absorption layer thickness, and uniform doping concentration on the PSC were estimated and studied using SCAPS-1D. The presence of a doping gradient increases carrier migration and considerably improves the photovoltaic performance of a PSC with a Cs2SnI6 absorption layer, according to an in-depth investigation of its photoelectric performance, band structure, and carrier dynamics. The gradient-doped perovskite absorption layer has a solar cell efficiency of 24.01%, which is significantly greater than the uniformly doped PSC. As a result, this work reveals that the gradient structured Cs2SnI6 PSC has a good photovoltaic performance, giving an effective technique for the solar power industry to manufacture affordable, efficient, and nontoxic gradient structured Cs-based PSCs.