Minimizing hydrogen vacancies to enable highly efficient hybrid perovskites.

Defect-induced non-radiative losses are currently limiting the performance of hybrid perovskite devices. Experimental reports have indicated the existence of point defects that act as detrimental non-radiative recombination centres under iodine-poor synthesis conditions. However, the microscopic nature of these defects is still unknown. Here we demonstrate that hydrogen vacancies can be present in high densities under iodine-poor conditions in the prototypical hybrid perovskite MAPbI3 (MA = CH3NH3). They act as very efficient non-radiative recombination centres with an exceptionally high carrier capture coefficient of 10-4 cm3 s-1. By contrast, the hydrogen vacancies in FAPbI3 [FA = CH(NH2)2] are much more difficult to form and have a capture coefficient that is three orders of magnitude lower. Our study unveils the critical but overlooked role of hydrogen vacancies in hybrid perovskites and rationalizes why FA is essential for realizing high efficiency in hybrid perovskite solar cells. Minimizing the incorporation of hydrogen vacancies is key to enabling the best performance of hybrid perovskites.