Accelerated formation of photoactive formamidinium-based lead triiodide perovskite crystals by the addition of copper iodide

Additions of copper iodide (CuI), rubidium iodide, or cesium iodide to perovskite precursor solutions accelerated the formation of the photoactive α-phase of formamidinium lead triiodide (FAPbI3) perovskite crystals. In particular, the addition of CuI suppresses the formation of low-dimensional perovskite phases, thereby reducing carrier transport. The first-principles calculations revealed that substituting Cu at the formamidinium site could maintain the effective mass ratios of the α-phase. The CuI addition to FAPbI3 is expected to enhance its photovoltaic properties. Moreover, introducing CuI into perovskite precursor solutions is suggested as a new approach to accelerate the formation of the photoactive α-FAPbI3 phase.