Gradient Interface in Oxygen-Doped Iron Pyrite Thin Films for Hybrid Solar Absorbers

To minimize losses arising from interfacial recombination and band misalignment between the absorber and hole transport layer (HTL) in thin-film solar cells, engineering the doping profile within the absorber layer has emerged as an effective strategy where the absorber layer and the HTL are formed with gradient interface through a controlled doping process. However, achieving precise control over the spatial distribution of dopants while maintaining favorable carrier transport remains a significant challenge. In this work, low energy oxygen implantation has been performed in FeS₂ thin films and a depth-resolved doping profile was obtained using secondary ion mass spectrometry. A direct correlation between the absolute oxygen content and the resulting hole concentration has been established. The role of spatially nonuniform doping has been systematically investigated through device-level TCAD simulations. The exponentially decaying carrier concentration leads to unfavorable band alignment, resulting in enhanced recombination losses with an efficiency of 3.27%. In contrast, a Gaussian-modulated doping profile, which enables improved band alignment and carrier transport by improving the efficiency to 5.46%, showing an enhancement of ∼67%. These results demonstrate that controlled formation of gradient interfaces through oxygen doping provides an effective route to suppress recombination and enhance carrier extraction, offering a reliable framework for the design of high-performance FeS₂-based photovoltaic devices.