Single-Crystal Perovskite Solar Cells Exhibit Over Half a Millimeter Electron Diffusion Length

Single-crystal halide perovskites exhibit photogenerated carriers of high mobility and long lifetime, making them excellent candidate materials for applications that demand thick semiconductors, such as ionizing radiation detectors, nuclear batteries, and concentrated photovoltaics. However, charge collection depreciates with increasing thickness, That requiring tens to hundreds of volts of external bias to extract charges from a thick perovskite layer, leading to a considerable amount of dark current and fast degradation of perovskite absorbers. However, extending the carrier diffusion length could mitigate many of the anticipated issues that prevent the practical utilization of perovskites in the abovementioned applications. Here we fabricate single-crystal MAPbI3 perovskite solar cells that are up to 400 times thicker than state-of-the-art perovskite polycrystalline films, yet retain high charge collection efficiency in the absence of an external bias. Cells with thicknesses of 110, 214, and 290 µm displayed power conversion efficiencies (PCEs) of 20.0, 18.4, and 14.7%, respectively. The remarkable persistence of these high PCEs, despite the increase in thickness, is a result of a long electron diffusion length in those cells, which we estimated, from the thickness-dependent short-circuit current, to be ~0.5 mm under 1-sun illumination. These results pave the way for adapting perovskite devices to optoelectronic applications in which a thick active layer is essential, such as direct X-ray detectors.