Optimizing photovoltaic efficiency in CZTS solar cells by investigating the role of different advanced materials as back surface field layer

The fast development of renewable resources requires high-performance and low-cost photovoltaic technologies. CZTS-based solar cells are promising candidates because of the earth-abundant materials and tunable bandgap. However, the efficiencies of these cells are hindered by interfacial recombination. In this study, we numerically analyze the incorporation of back-surface field (BSF) layers to reduce the current losses enhancing the efficiency of a CZTS device. By using systematic SCAPS-1D simulations, we investigated eight different BSF materials (PTAA, Zn₃P₂, SnS, MoOx, CuI, CNTS, V₂O₅, and Cu₂O) leading us to conclude Cu₂O as the one with the highest efficiency, resulting in a record power conversion efficiency (PCE) of 26.19% (~ 110% enhancement with respect to the reference cell performing 12.82%). The precise Cu₂O band alignment (CBO: 1.0 eV, VBO: -0.28 eV) is the origin of an effective suppression of carrier recombination while facilitating an effective hole extraction. Promising results in terms of PCE, which remains on the order of 20%, are also achieved for an increased operational temperature of the simulated devices up to 420 K. In addition, further analyses show that the use of V₂O₅ and CuI as BSF exceeds the conventional design as well (PCE > 24%), when the defect densities are below 10¹⁴ cm^-3 and the shunt resistance is > 10⁴Ω·cm². Thus, these studies clearly illustrate whether purposeful BSF integration can surmount fundamental shortcomings of CZTS solar cells, providing a feasible route to viable commercial devices.