Phase‐Pure Iron Pyrite Nanocrystals as Air‐Stable Hole‐Transport Materials for Low‐Cost Perovskite Solar Cells

Spiro‐OMeTAD is a commonly used organic hole‐transport material (HTM) in MAPbI 3 ‐based perovskite solar cells (PSCs) for achieving high efficiency. However, its hydrophilic nature compromises device stability and performance reproducibility, especially under ambient conditions. In this study, PSCs are fabricated under ambient conditions, and phase‐pure iron pyrite nanocrystals (FeS 2 NCs) are synthesized and utilized as HTM. Using iron pyrite as the HTM leads to a 22% increase in device short‐circuit current density ( J SC ) compared to Spiro‐OMeTAD, resulting in enhanced PSC performance. This confirms FeS 2 NCs as a promising HTM for PSCs. Iron pyrite improves the extraction of photogenerated charge carriers compared to Spiro‐OMeTAD, indicating a superior extraction layer. Furthermore, the longer stability of the iron pyrite layer under humid conditions is compared to the Spiro‐OMeTAD layer, as demonstrated by contact angle measurements. This improvement helps prevent humidity‐induced degradation of the perovskite layer. Transient photocurrent studies under reverse bias conditions reveal fewer defects at the perovskite/iron pyrite interface, suggesting a defect passivation effect of FeS 2 NCs. This study demonstrates that iron pyrite can serve as an effective HTM to enhance the performance and stability of low‐cost PSCs fabricated under ambient conditions.