The Bright Side and Dark Side of Hybrid Organic–Inorganic Perovskites

The previously developed bistable amphoteric native defect (BAND) model is used for a comprehensive explanation of the unique photophysical properties and for understanding the remarkable performance of perovskites as photovoltaic materials. It is shown that the amphoteric defects in donor (acceptor) configuration capture a fraction of photoexcited electrons (holes) dividing them into two groups: higher energy bright and lower energy dark electrons (holes). The spatial separation of the dark electrons and the dark holes and the k-space separation of the bright and the dark charge carriers reduce electron hole recombination rates, emulating the properties of an ideal photovoltaic material with a balanced, spatially separated transport of electrons and holes. The BAND model also offers a straightforward explanation for the exceptional insensitivity of the photovoltaic performance of polycrystalline perovskite films to structural and optical inhomogeneities. The blue-shifted radiative recombination of bright electrons and holes results in a large anti-Stokes effect that provides a quantitative explanation for the spectral dependence of the laser cooling effect measured in perovskite platelets. National Research Foundation (NRF) Accepted version This work (JWA, WW) was supported by the Singapore National Research Foundation through the Intra-CREATE Collaborative Grant NRF2018-ITC001-001. B. W. acknowledges the support from the National Natural Science Foundation of China (NFSC) (grant No. 51802331), Science and Technology Program of Guangzhou (No. 2019050001). T. C. S. acknowledges the support of Nanyang Technological University under its internal grant (M4082480); and the National Research Foundation (NRF) Singapore under its Competitive Research Program (NRF-CRP14-2014-03) and its NRF Investigatorship (NRF-NRFI-2018-04).