报告题目：Radiative versus non-radiative recombination in perovskites: from individual nano-crystals to films

报告人：   Prof. Ivan Scheblykin（瑞典隆德大学）

报告时间：2019年6月20日（星期四）下午15:00-16:00

报告地点：激光光谱研究所三层报告厅

报告简介：

  Charge recombination in semiconductors depends on concentration of electrons, holes, traps, non-radiative recombination centres, trapping cross sections, radiative recombination rate and many other factors. All these makes it difficult to comprehend the recombination kinetics in metal halide perovskites (MHP) where most of the mentioned parameters either not known or/and vary enormously from sample to sample. Photoluminescence (PL) is an important tool allowing following the fate of the photogenerated charges by monitoring their radiative recombination in competition with the other recombination processes. Among many contradictory observations and believes regarding PL, I would mention one here. The common knowledge in the photovoltaic community is that the larger the MHP crystal (micrometres and more) the lower the defect concentration and higher PL quantum yield (PLQY). At the same time, for the LED community where PLQY is the most crucial, MHP nanocrystals with sizes less than 100 nm are considered to be the best for reaching efficient devices. These two statements seem to contradict to each other and need an explanation.

    I will talk about the dependence of PLQY on crystal size, temperature, and the role of different types of non-radiative centres. Experiments carried out on individual nano- and micro crystals and intact films will be discussed. A particularly intriguing phenomenon which we believe is inherent to MHP semiconductors is a stochastic activation and de-activation of very strong non-radiative centres often called “super-traps”. This effect is clearly manifested as PL blinking of nano- and micro-crystals of MHPs and PL flickering of local areas in thin films. Implications of PL blinking and its usage for unravelling MHP physics will be demonstrated.

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        [5]  M. Gerhard et al, Nature Communications 10 (1), 1698 (2019).