Boosting Photoluminescence in MAPbBr3 Single Crystals through Laser-Based Surface Modification

Single crystals (SCs) of metal halide perovskites show promise in improving the good optoelectronic characteristics of their polycrystalline counterparts, yet the surface losses represent a substantial drawback in the form of nonradiative recombination. We show that blue CW laser treatment of MAPbBr3 perovskite SCs results in the crystal surface modification, which includes the formation of an upper PbBr2 film as well as an underlying layer of a crystalline perovskite, which demonstrates ≈75 meV extended band gap. As a result, photoluminescence improves up to 2 orders of magnitude after the treatment. We suggest that the extended-band gap MAPbBr3 has a distorted crystalline lattice formed due to tensile strain after the laser-induced partial decomposition of CH3NH3+ in the presence of O2. Formic acid and methylamine are formed as byproducts to passivate the distorted MAPbBr3 layer and protect perovskite structures from adverse influences of the environment such as water-induced degradation.