Chouhan Lata, Ghimire Sushant, Biju Vasudevanpillai
Research Institute for Electronic Science and Graduate School of Environmental Science, Hokkaido University Sapporo, Hokkaido, 001-0020, Japan.
Angew Chem Int Ed Engl. 2019 Apr 1;58(15):4875-4879. doi: 10.1002/anie.201900061. Epub 2019 Feb 28.
Moisture- or oxidation-induced degradation is a major challenge in the advancement of perovskites-based technology. The oxidation is caused by electron transfer from a photo-excited perovskite nanocrystal to oxygen and the formation of superoxide that disintegrates the perovskite structure. In air, the emission intensity of a methylammonium lead iodide (MAPbI ) perovskite nanocrystal continuously decreases, whereas a nanocrystal in argon or a polymer shows exceptionally stable emission intensity. Surprisingly, in air, the emission intensity of a nanocrystal with long-lived OFF states completely recovers after the OFF state. This property, along with the rate of non-radiative relaxation that exceeds the rate of electron transfer suggest that the perovskite nanocrystals produce and react with superoxide in the excited neutral state, but not in the ionized state. In other words, the ultrafast non-radiative relaxation in the ionized state hinders electron transfer to oxygen and prevents oxidation of perovskites.
水分或氧化引发的降解是钙钛矿基技术发展中的一个重大挑战。氧化是由光激发的钙钛矿纳米晶体向氧气的电子转移以及超氧化物的形成引起的，超氧化物会分解钙钛矿结构。在空气中，甲基碘化铅（MAPbI）钙钛矿纳米晶体的发射强度持续下降，而在氩气或聚合物中的纳米晶体则表现出异常稳定的发射强度。令人惊讶的是，在空气中，具有长寿命关态的纳米晶体的发射强度在关态之后会完全恢复。这一特性，连同非辐射弛豫速率超过电子转移速率，表明钙钛矿纳米晶体在激发中性态而非电离态下产生并与超氧化物反应。换句话说，电离态下的超快非辐射弛豫阻碍了电子向氧气的转移，并防止了钙钛矿的氧化。
