Numerical simulation and optimization of BaZrSe₃/ZnS heterojunction solar cells: achieving high performance

In this work, a ZnO:Al/ZnO/ZnS/BaZrSe₃/Au heterojunction solar cell was numerically investigated using SCAPS-1D to optimize its structural and electronic parameters for high photovoltaic performance. The effects of absorber thickness (50 nm-6.0 μm), buffer layer thickness (10-100 nm), doping densities, defect states, operating temperature, and back metal contacts were systematically studied. The results revealed that increasing the BaZrSe₃ absorber thickness enhanced the short-circuit current density (J _sc) due to improved light absorption, with an optimum thickness of 2.0 μm balancing carrier generation and recombination. The ZnS buffer layer exhibited optimum performance at 20 nm, ensuring efficient charge transfer without increasing resistive losses. The acceptor doping concentration in BaZrSe₃ strongly influenced the device properties, with N _A = 10¹⁸ cm^-3 yielding the maximum PCE of 22.77%. Similarly, an optimized donor doping density of 10¹⁹ cm^-3 in the buffer enhanced carrier extraction. Defect density analysis showed that PCE remained stable up to N _T = 10¹⁴ cm^-3, beyond which recombination dominated, reducing efficiency. Temperature-dependent simulations indicated a decline in PCE from 22.92% at 300 K to 17.87% at 360 K due to enhanced carrier recombination. Finally, the choice of back contact significantly affected performance, with a high work-function metal (5.9 eV) achieving superior results, including PCE = 29.46%, V _oc = 0.7528 V, J _sc = 46.38 mA cm^-2, and FF = 84.37%. These results highlight the promising potential of BaZrSe₃ as a lead free absorber material for next-generation thin film solar cells, where optimization of thickness, doping, and contact engineering play a crucial role in maximizing device efficiency.