Photoelectromagnetic Effect in Hybrid Lead Iodide Perovskite

This is the first report of the photoelectromagnetic (PEM) effect in single crystals and thin films of pure and mixed cation methylammonium lead iodide. A combination of photoconductance (PC) and PEM measurements has a unique capability to characterize bulk recombination unaffected by surface effects. We report lower limits to the bulk carrier lifetime, the carrier mobility, and the bulk diffusion length in methylammonium lead iodide (MAPbI₃) and acetamidinium-substituted lead iodide (MA_0.9AA_0.1PbI₃) perovskite single crystals and thin films. Data show that the oversized acetamidinium cation passivates the bulk, leading to a 10x longer bulk recombination lifetime. The ratio of PC to PEM signal allows a direct measurement of the bulk recombination velocity (BRV) that determines the open-circuit voltage in solar cells. Surprisingly, the BRVs of the MAPbI₃ single crystal and polycrystalline thin film are comparable even though the lifetime changes by 2 orders of magnitude, explaining why the performance of single-crystal perovskite solar cells is not better than state-of-art thin-film perovskite solar cells. PEM measurement is a straightforward measurement tool that can measure and optimize the transport and recombination properties of solar cell materials.