Air stable, photosensitive, phase pure iron pyrite nanocrystal thin films for photovoltaic application

Iron pyrite (FeS₂) is a naturally abundant and nontoxic photovoltaic material that can potentially make devices as efficient as silicon-based ones; however existing iron pyrite photovoltaic devices contain thermodynamically unstable FeS₂ film surfaces that lead to low open circuit voltages. We report the rational synthesis of phase pure, highly crystalline cubic FeS₂ nanocrystals (NCs) using a trioctylphosphine oxide (TOPO) assisted hot-injection method. The synthesized pyrite NC films have excellent air stability over one year. In contrast, obvious surface decomposition was observed on the surface of FeS₂ NCs synthesized without TOPO. A high carrier mobility of 80 cm²/(V s) and a strong photoconductivity were observed for the first time for pyrite films at room temperature. Our results indicate that TOPO passivates both iron and sulfur atoms on FeS₂ NC surfaces, efficiently inhibiting surface decomposition.