The sulde perovskite LaYS 3 has been recently identied as a promising wide band gap photoabsorber material by computational screening techniques. In this study, we combine experiment and theory to comprehensively characterize LaYS 3 thin lms produced by sulfurization of sputter-deposited precursors. An attractive feature of LaYS 3 is its optimal band gap (2.0 eV) for application as a wide-band gap photoabsorber in 1 tandem solar energy conversion devices. Promisingly, the LaYS 3 lms are photoconductive, with a grain size in excess of 1 µm and comparable recombination timescales to state-of-the-art hybrid halide perovskite absorbers. Although the fabrication of solar cells based on LaYS 3 absorbers is complicated by the high temperature necessary to grow the compound, complete solar cells could be produced in this work by growing LaYS 3 on refractory metal back contacts. These are the rst reported solar cells based on a sulde perovskite absorber. A major reason for their poor performance could be the highly localized trap states observed directly by photoluminescence imaging of LaYS 3 , which may also explain the surprisingly long carrier lifetimes and the low carrier mobility found in this material.

The light-soaking effect is the observation that under constant illumination the measured power conversion efficiency of certain solar cells changes as a function of time. The theory of the light-soaking in metal halide perovskites is at present incomplete. In this report, we employ steady-state microwave conductivity, a contactless probe of electronic properties of semiconductors, to study the light-soaking effect in metal halide perovskites. By illuminating isolated thin films of two mixed-cation perovskites with AM1.5 solar illumination, we observe a continual increase in photoconductance over a period of many (>12) hours. We can fit the experimentally observed changes in photoconductance to a stretched exponential function, in an analogous manner to bias-stressed thin-film transistors. The information provided in this report should help the community better understand one of the most perplexing open problems in the field of perovskite solar cells and, ultimately, lead to more robust and predictable devices.

A strategy is demonstrated to evaluate the carrier mobility in-plane and out-of-plane using contactless time resolved microwave conductivity.