These results provide direct proof for the superior optoelectronic properties of perovskite monocrystalline films in devices over their polycrystalline counterparts. With the millimeter sized bulk single crystal, it’s hard to make a high efficiency solar cell. However, Dong et al. fabricated lateral structure perovskite single crystal solar cells via piezoelectric poling. A highest PCE of 5.36% can be reached at 170 K which yields an efficiency enhancement of 44 folds of the polycrystalline film