Scalable Phosphorus Doping of p‑Type FeS₂ Microcrystals for Photovoltaic Applications

Pyrite FeS₂ is an Earth-abundant semiconductor with the potential to deliver the lowest-cost photovoltaic solutions available today. However, progress has been limited by poor control over doping and surface defect chemistry, leading to consistently low device efficiencies. In this work, we demonstrate for the first time a truly scalable approach to achieve p-type conductivity of pyrite microcrystals using phosphorus via the liquid salt growth method. We systematically explore three established doping strategies for semiconductors and identify the successful route involving the use of a FeS + P precursor containing the FeP₄ phase. Hot probe measurements confirm p-type conductivity. Neutral sources such as elemental phosphorus are shown to be thermodynamically unsuitable and fail to induce p-type behavior. This study also identifies a phosphorus compound suitable for producing p-type FeS₂ microcrystals, offering a new foundation for the development of pyrite photovoltaic devices.