First-Principles Investigation of Defect States and Their Influence on the Electronic Properties of Kesterite Solar Cell Absorbers for Nigerian Photovoltaic Applications

Background: Kesterite Cu2ZnSnS4 solar cell absorbers offer a pathway to low-cost, earth-abundant photovoltaics free from indium and tellurium scarcity constraints, yet intrinsic defect states remain a primary efficiency limitation whose electronic origins require thorough theoretical investigation. Aim: This study employed first-principles density functional theory calculations to investigate dominant defect states in CZTS and their influence on electronic properties relevant to photovoltaic performance. Methods: Density functional theory calculations with hybrid HSE06 exchange-correlation functional were performed using the Vienna ab initio Simulation Package. Defect formation energies, charge transition levels, and carrier capture cross-sections were computed for 22 intrinsic point defects and five defect complexes as a function of chemical potential conditions corresponding to Cu-poor and Zn-rich synthesis environments. Results: Cu vacancies and CuZn antisites were identified as the dominant acceptors with shallow transition levels at 0.12 and 0.18 eV above the valence band maximum. SnZn antisites formed deep compensating donor states at 0.38 eV below the conduction band minimum, constituting the principal non-radiative recombination centres. Cu-poor synthesis conditions minimised deep defect formation by raising the formation energy of SnZn antisites. Conclusion: Synthesis under stringently Cu-poor conditions is theoretically justified as the primary strategy for minimising non-radiative recombination in CZTS absorbers. The established defect landscape provides a rigorous foundation for optimising CZTS solar cell fabrication processes in Nigerian research laboratories. Keywords: kesterite, CZTS, first-principles, defect states, solar cell.