Abstract
Nonradiative losses in semiconductors are related to defects. At cryogenic temperatures, defect-related photoluminescence (PL) at energies lower than the band-edge PL is observed in methylammonium lead triiodide perovskite. We applied multispectral PL imaging to samples prepared by two different procedures and exhibiting 1 order of magnitude different PL quantum yield (PLQY). The high-PLQY sample showed concentration of the emitting defect sites around 1012-1013 cm-3. No correlation between PLQY and the relative intensity of the defect emission was found when micrometer-sized local regions of the same sample were compared. However, a clear positive correlation between the lower PLQY and higher defect emission was observed when two preparation methods were contrasted. Therefore, although the emissive defects are not connected directly with the nonradiative centers and may be spatially separated at the nano scale, chemical processes during the perovskite synthesis promote/prevent formation of both types of defects at the same time.
Highlights
Nonradiative losses in semiconductors are related to defects
An intriguing feature of metal halide perovskite (MHP) is that most of these defects are quite harmless for device performance, which has engaged the community to discuss such a feature of MHPs as defect tolerance.[10−13] the effect of defects in MHPs is obvious because, as for any semiconductor, they do influence charge recombination, charge mobility, photoluminescence yield, material degradation, and so on.[14−25]
Besides the NR recombination rate being dependent on the sample preparation, environment, light irradiation,[28] sample age, and so on, it varies greatly at the micro and nano scales within the very same sample.[15,22,29,30]
Summary
Nonradiative losses in semiconductors are related to defects. At cryogenic temperatures, defect-related photoluminescence (PL) at energies lower than the band-edge PL is observed in methylammonium lead triiodide perovskite. Note that the nature of the excitations localized at shallow defect sites can be excitonic (trapped excitons).[33] a defect-related PL at energies lower than the band-edge can occur at cryogenic temperatures.[31,33−41]
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