Spike‐Type Band Alignment via in 2 Se 3 /CuI Charge‐Transport Engineering Enables 26% Efficient Lead‐Free RbSn 0.5
Md. Al Amin, Md. Sanwar Hossain, Md. Feroz Ali, Md Shafiul Alam, Mohammad Ali, Mohammed A. AlAqilABSTRACT
Replacing toxic Pb‐based absorbers with eco‐friendly alternatives remains a critical requirement for the sustainable commercialization of perovskite solar cells (PSCs). Here, a fully Cd‐free, lead‐free heterojunction PSC with the architecture Al/FTO/In 2 Se 3 /RbSn 0.5 Ge 0.5 I 3 /CuI/Ni is systematically designed and optimized using SCAPS‐1D. Seven electron transport layers (In 3 Se 4 , CdS, WS 2 , IGZO, SnS 2 , ZnSe, In 2 Se 3 ) and five hole transport layers (GO, GQD, PEDOT:PSS, CuSCN, CuI) are screened, identifying In 2 Se 3 and CuI as the optimal pair owing to their favorable spike‐type conduction‐band offset (+0.20 eV) and zero‐eV valence‐band offset, which suppress non‐radiative interfacial recombination as confirmed by Nyquist impedance analysis. Comprehensive optimization of absorber thickness, carrier concentration, bulk and interface defect densities, operating temperature, back‐contact work function, parasitic resistances, capacitance–voltage and capacitance–frequency response, carrier generation/recombination dynamics, and electric‐field distribution is performed. Under optimized conditions, the device delivers a power conversion efficiency of 26.01%, with Voc = 0.85 V, Jsc = 38.43 mA cm − 2 , and FF = 79.70%, surpassing previously reported RbSn 0.5 Ge 0.5 I 3 ‐based architectures. These findings establish clear design guidelines for high‐efficiency, environmentally benign Sn–Ge perovskite photovoltaics.