Bulk Defect Suppression of Micrometer-Thick Perovskite Single Crystals Enables Stable Photovoltaics

Metal halide perovskite single crystals have become emerging candidates for photovoltaic applications due to their better optoelectronic properties and higher stability than their polycrystalline thin-film counterparts. However, in contrast to the rapid enhancement of power conversion efficiency (PCE), the operational stability of single-crystal perovskite solar cells (PSCs) remains far lagging behind. Herein, it is discovered that widely investigated 20 μm-thick single-crystal PSCs show poor operational stability, which is assigned to low crystal quality of these thin single crystals. Subsequently, the crystal quality of formamidinium0.55methylammonium0.45 lead triiodide (FA0.55MA0.45PbI3) thin single crystals are optimized by adjusting the ion diffusion velocity in confined space, leading to lower trap density, larger ion migration activation energy, and reduced light-induced degradation of material properties. As a result, stable single-crystal PSCs with no efficiency degradation after 330 h of continuous operation at the maximum power point under 1 sun illumination are achieved. Moreover, thickness-dependent device efficiency discloses an ultralong carrier transport length of 200 μm in FA0.55MA0.45PbI3 thin single crystals, which is instructive for developing lateral-structure solar cells.