Role of A‐Site Composition in Charge Transport in Lead Iodide Perovskites

Abstract

As the power conversion efficiency and stability of solar cells based on metal halide perovskites continue to improve, the community increasingly relies on compounds formed of mixed cations and mixed halides for the highest performing devices. The result is that device engineers now have a potentially infinite number of compositions to choose from. While this has provided a large scope for optimization, it has increased complexity of the field, and the rationale for choosing one composition over another remains somewhat empirical. Herein, the distribution of electronic properties for a range of lead iodide perovskite thin films is mapped. The relative percentages of methylammonium, formamidinium, and cesium are varied, and the electronic properties are measured with time‐resolved microwave conductivity, a contactless technique enabling extraction of electronic properties of isolated films of semiconductors. It is found a small amount of Cs leads to larger carrier mobilities and longer carrier lifetimes and that compositions with a tolerance factor close to 0.9 generally show lower performance that those closer to 0.8 or 1.0.

Keywords

• cesium lead iodide
• formamidinium lead iodide
• methylammonium lead iodide
• perovskites
• time-resolved microwave conductivities