Unravelling the Mechanism of Photo-activated Ion Dynamics in Organic-Inorganic Perovskites

Study of the emission behavior of organometal halide perovskites CH3NH3PbBr3 as function of excitation intensity by using photoluminescence (PL) and time-resolved photoluminescence (TRPL) techniques reveals the photoactivated mobile ion can evidently impact carrier dynamics in the minutes time scale. We observe that PL intensity and PL decay exhibit excitation intensity dependent reductions in the minute time scale under continuous excitation at constant intensity. It has been confirmed that the carrier recombination intimately related to the density of photoexcited carriers. However, this long response time suggests photo-activated ion migration, rather than photo-generated electrons and holes, are responsible for the observed change in carrier dynamics. The observations provide insight into the nonradiative behavior of perovskite material under illumination. Because free carrier recombination process is linked to charge separation/transportation efficiency, these key findings are useful for understanding of instability of perovskite solar cells.