Interface-Dependent Radiative and Nonradiative Recombination in Perovskite Solar Cells

Interfacial engineering has shown to play an essential role to optimize recombination losses in perovskite solar cells; however, an in-depth understanding of the various loss mechanisms is still underway. Herein, we study the charge transfer process and reveal the primary recombination mechanism at inorganic electron-transporting contacts such as TiO2 and its modified organic rivals. The modifiers are chemically ([6,6]-phenyl C-61 butyric acid, PC(60)BA) or physically ([6,6]-phenyl C-6l butyric acid methyl ester, PC60BM and C-60) attached fullerene to the TiO2 surface to passivate the density of surface states. We do not observe any change in morphology, crystallinity, and bulk defect density of halide perovskite (CH3NH3PbI3 in this case) upon interface modification. However, we observe compelling results via photoluminescence and electroluminescence studies that the recombination dynamics at both time scales (slow and fast) are largely influenced by the choice of the selective contact. We note a strong correlation between the hysteresis and the so-called slow charge dynamics, both significantly influenced by the characteristics of the selective contact, for example, the presence of surface traps at the selective contact not only shows a larger hysteresis but also leads to higher charge accumulation at the interface and distinguishable slow dynamics (a slower stabilization of recombination dynamics at a time scale of several minutes).