Organo-metal halide perovskites are promising solution-processed semiconductors, however, they possess diverse and largely not understood non-radiative mechanisms. Here, we resolve contributions of individual non-radiative recombination centers (quenchers) in nanocrystals of methylammonium lead iodide by studying their photoluminescence blinking caused by random switching of quenchers between active and passive states. We propose a model to describe the observed reduction of blinking upon cooling and determine energetic barriers of 0.2 to 0.8 eV for enabling the switching process, which points to ion migration as the underlying mechanism. Moreover, due to the strong influence of individual quenchers, the crystals show very individually-shaped photoluminescence enhancement upon cooling, suggesting that the high variety of activation energies of the PL enhancement reported in literature is not related to intrinsic properties but rather to the defect chemistry. Stabilizing the fluctuating quenchers in their passive states thus appears to be a promising strategy for improving the material quality.
Fundmental comprehension of light-induced processes of perovskites are still scarce. One active debate surrounds the influence of excess lead iodide (PbI 2) on device performance, as well as optoelectronic properties, where both beneficial and detrimental traits have been reported. Here, we study its impact on the charge-carrier recombination kinetics by simultaneously acquiring photoluminescence quantum yield and time-resolved photoluminescence as a function of excitation wavelength (450 nm-780 nm). The presence of PbI 2 in the perovskite film is identified via a unique spectroscopic signature in the PLQY spectrum. Probing the recombination in the presence and absence of this signature, we detect a radiative bimolecular recombination mechanism induced by PbI 2. Spatially resolving the photoluminescence, we determine that this radiative process occurs in a small volume at the PbI 2 /perovskite interface, which is only active when charge carriers are generated in PbI 2 , and therefore provide deeper insight into how excess PbI 2 may improve the properties of perovskite based devices.
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