Influence of morphology on photoluminescence properties of methylammonium lead tribromide films

The morphology of hybrid perovskite thin films plays a crucial role for their photophysical properties. However, the underlying mechanisms are still unclear. To gain further insight into this phenomenon, methylammonium lead tribromide films of different morphology were investigated using photoluminescence spectroscopy. Photostability measurements demonstrate three mechanisms: (A) reversible degradation of the photoluminescence, depending positively on the grain-boundary density, which is presumably caused by photo-induced bromide vacancies, (B) enhancement of the photoluminescence intensity in the presence of oxygen and moisture and (C) destruction of the perovskite after several minutes of ultraviolet illumination with excitation power above 100 W/cm(2). Both the intensity and the lifetime of the photoluminescence were significantly smaller in films with micrometer-sized crystallites compared to granular films. This is ascribed to crystals being partially isolated in the former, causing smaller diffusion lengths, whereas the carriers in the granular films can diffuse from grain to grain resulting in higher photoluminescence lifetime and intensity