Salutary impact of spontaneous oxidation in CH₃NH₃SnI₃ on CZTS-based solar cell

From the time of discovery, CH₃NH₃SnI₃ has been a promising candidate in photovoltaics due to its outstanding optoelectronic properties. However, stabilization was not easy to achieve in CH₃NH₃SnI₃-based solar cells. Because CH₃NH₃SnI₃ was used as an absorber, its naturally-occurring self-doping property spontaneously modified band alignment, which increased carrier recombination and decreased the efficiency of solar cell gradually. In this paper, for the first time, we have presented detailed study on use of CH₃NH₃SnI₃ as a hole transport layer in prototype solar cell having configuration: CH₃NH₃SnI₃/CZTS/CdS/ZnO/AZO, using SCAPS software. To understand the effect of spontaneous self-doping property of CH₃NH₃SnI₃ on solar cell performance, the analysis of variation in solar cell performance parameters, band alignment conduction band, valance band, Fermi levels, charge density, current density, conductance, capacitance and recombination rate was performed as a function of increasing CH₃NH₃SnI₃ carrier concentration. It was found that, when used as an hole transport layer, the inherent self-doping property of CH₃NH₃SnI₃ became a helpful trait to increase hole extraction and spontaneously enhanced our device efficiency. Thus, the inherent self-doping property of CH₃NH₃SnI₃ transformed from curse to boon when we leveraged CH₃NH₃SnI₃ as an hole transport layer in our solar cell device.