Oxidative Passivation of Metal Halide Perovskites

Abstract

The authors propose a comprehensive mechanism for the improvement to optoelectronic properties observed when metal halide perovskites are exposed to light and air in ambient conditions, a process known as photo-brightening. Hydrogen peroxide is shown to be the active reagent responsible, and the authors demonstrate its use as a simple and fast post-treatment, resulting in substantial improvements to photoluminescence and photovoltaic device performance.

Investigation of the Role of the Environment on the Photoluminescence and the Exciton Relaxation of CsPbBr3 Nanocrystals Thin Films

“…Moreover, beyond the static effects, the interaction with WA also modifies the PL relaxation dynamics, which become slower in WA. While this effect can be described as an average lifetime increase, also observed in MAPbI 3 films [23], our data evidence that this effect, in our sample, cannot be simply explained by the suppression of a non-radiative decay channel that increases the lifetimes. In particular, we observe that no variations are present both in the FE trapping lifetime τ 1 and in the FE relaxation time τ 2 , while the variation affects the pre-exponential amplitudes, with a reduction of the FE trapping and the increase of the FE relaxation one.…”

“…To understand the processes leading to the PL intensity dependence on the environment in Sample #F and the origin of the strongly different behavior observed in Sample #A, it is first useful to remind that the PL intensity increase observed in both samples is qualitatively similar to the one reported both for lead halide perovskites polycrystalline thin films [22][23][24][25] and single crystals [26,27]. In all these systems, the PL intensity increase in WA has been ascribed to oxygen or moisture induced passivation of halide vacancies, which reduces the non-radiative decay rate, thus increasing the PLQY and the PL lifetime.…”

“…The presence of PL enhancement in WA in our samples thus suggests that the co-precipitation growth method leads to the formation of NCs with a higher density of bromine vacancies on the surface with respect to NCs grown by hot-injection. It is also important to underline that the very high PLQY of the just deposited films and the relatively small PL intensity increase of Sample #F suggest a defect density much smaller than the one of bulk polycrystalline films and single crystals, typically showing much lower initial PLQY and much higher PL enhancement in WA [22][23][24][25][26][27]. We also underline that the observed small red-shift and the narrowing of the FE and BE bands are consistent with previous results on MAPbI 3 thin films [24], ascribed to defects passivation without irreversible degradation.…”

“…To date, it has been demonstrated that lead halide perovskites can be degraded by many factors such as temperature [13], light exposure [13][14][15][16][17], and interaction with oxygen and moisture [18][19][20][21]. Interestingly, despite the reports of material degradation due to its interaction with air, several experiments demonstrated that the interaction with oxygen and wet air can also improve the light emission and the device performances of bulk polycrystalline thin films [22][23][24][25] and single crystals [26,27]. This effect, typically reversible, is generally ascribed to the oxygen passivation of halide vacancies taking place at the air-perovskite interface, which decreases the excitation non-radiative decay rate, thus increasing the photoluminescence (PL) intensity and decreasing the PL decay rate [22][23][24][25][26][27].…”

Photobrightening in Lead Halide Perovskites: Observations, Mechanisms, and Future Potential

“…Other works have proposed mechanisms to understand the photobrightening effect related to atmospheric conditions . Illumination in general generates defects such as halide vacancies (e.g., through light‐induced ion migration) or atomic lead species .…”