Hybrid organic-inorganic perovskites have been used in optoelectronic devices including solar cells, photodetectors, light-emitting diodes and lasers, but the surface of hybrid perovskites is prone to surface defects, where charge carriers are trapped in the semiconducting material. To solve this problem, the crystal surface must be passivated. Researchers describe testing hybrid organic-inorganic perovskite crystals treated with benzylamine to investigate the mechanisms by which the surface of the crystal is passivated, and traps states are reduced.