Structure, Morphology, and Photovoltaic Implications of Halide Alloying in Lead-Free Cs_3Sb_2Cl_xI_(9-x) 2D-Layered Perovskites

摘要

Compositional tuning is a major driving force behind the excellent optoelectronicproperties observed in typical Pb-based perovskites. For lead-free perovskitederivatives, a challenge to understand the connection between compositionaltuning and intrinsic optoelectronic properties, hence a barrier toward boostingtheir performance, comes from the fact that multiple crystalline substructurescan form based on composition, film processing, or both. Especially with lowerdimensional (0D, 1D, and 2D) substructures, the particular polymorph present inthe film can be a greater determinant of optoelectronic properties than thecomposition itself. Herein, a simple method to alloy the halide site in all-inorganiclead-free Cs_3Sb_2I_9 films is reported while maintaining a consistent 2D-layeredsubstructure, as a means to independently study the photovoltaic implicationsof halide substitution. A broad suite of spectroscopy and device measurementsis used to identify an optimal stoichiometric substitution of chloride for iodide(≈8 mol%, measured) that balances both intrinsic and bulk optoelectronicproperties to achieve a top power conversion efficiency of 2.2%. This workunderscores the importance of controlling substructure while investigating theimpacts of compositional tuning for the development of lead-free perovskites andmore broadly validates the approach toward realizing lead-free alternativeperovskite solar technologies.