Tuning the rear conduction band offset in CIGS thin-film solar cells using Sb2(S1−xSex)3 electron blocking layer to improve efficiency

• Sb 2 (S,Se) 3 used as a rear-side electron blocking layer (EBL) in CIGS solar cells. • Tunable Se/(S + Se) ratio controls band alignment and suppresses rear recombination. • Sb 2 S 3 -based EBL introduces a 0.55 eV conduction band barrier at rear interface. • V oc enhancement achieved due to optimized electron barrier at back interface. • Power conversion efficiency improved by ∼3 % with optimized EBL design. The integration of an electron blocking layer (EBL) is a promising strategy to enhance the open-circuit voltage (V oc ) and efficiency of CIGS (Cu(In,Ga)Se 2 ) solar cells. In this study, we employ Sb 2 (S,Se) 3 as a rear-interface EBL within a numerical simulation framework based on a high-performance CIGS reference cell (23.35 % efficiency). The Sb 2 (S,Se) 3 layer creates a conduction band offset that acts as an effective barrier to electron backflow, thereby suppressing carrier recombination at the rear contact. Comprehensive simulations are conducted to analyze how the electron barrier influences the photovoltaic output, focusing on key parameters including interface defect density at the EBL/CIGS and within the CIGS absorber, rear surface recombination velocity, and Nyquist characteristics. The conduction band alignment at the Sb 2 (S 1−x Se x ) 3 /CIGS is tuned by varying the Se-to-S ratio, enabling control over the conduction band offset to optimize carrier selectivity. The results reveal that for compositions with x < 0.7, the device benefits from a favorable conduction band barrier, resulting in a notable increase in V oc due to suppressed recombination at the rear interface. The slight increase in J sc results from improved long-wavelength carrier collection due to reduced rear interface recombination enabled by the optimized conduction band alignment of the Sb 2 S 3 layer. Under optimized conditions, results show an efficiency of 26.18 %, representing a ∼3 % improvement relative to the reference device. While these simulated values exceed experimental records for CIGS cells, they highlight the theoretical potential of Sb 2 (S,Se) 3 -based rear interface engineering as a viable pathway toward next-generation high-efficiency CIGS cells.