Abstract
Slow electron-hole recombination, characterized by the bimolecular coefficient k2 in hybrid organic-inorganic perovskites (HOIPs), is a key to their outstanding photovoltaic performance. The measured k2 in HOIPs strongly deviates from k2 ∝ T-3/2 (T is the temperature) in typical direct-gap semiconductors. Here we show that the observed temperature dependence can be quantitatively accounted for by phonon-assisted recombination of electrons and holes located at the band extrema, which become indirect due to the Rashba effect. Polar optical phonons are most effective in facilitating this indirect recombination. The variation in k2 in HOIPs among different studies in the literature can be attributed to different Rashba strengths in their samples. Our results indicate that the confluence of the Rashba effect and polar coupling transform HOIPs into a unique indirect semiconductor that can accommodate both strong optical absorption and slow carrier dynamics.
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