Carrier recombination in CH3NH3PbI3: why is it a slow process?

Abstract

In methylammonium lead iodide (MAPbI₃), a slow recombination process of photogenerated carriers has often been considered to be the most intriguing property of the material resulting in high-efficiency perovskite solar cells. In spite of intense research over a decade or so, a complete understanding of carrier recombination dynamics in MAPbI₃has remained inconclusive. In this regard, several microscopic processes have been proposed so far in order to explain the slow recombination pathways (both radiative and non-radiative), such as the existence of shallow defects, a weak electron-phonon coupling, presence of ferroelectric domains, screening of band-edge charges through the formation of polarons, occurrence of the Rashba splitting in the band(s), and photon-recycling in the material. Based on the up-to-date findings, we have critically assessed each of these proposals/models to shed light on the origin of a slow recombination process in MAPbI₃. In this review, we have presented the interplay between the mechanisms and our views/perspectives in determining the likely processes, which may dictate the recombination dynamics in the material. We have also deliberated on their interdependences in decoupling contributions of different recombination processes.

Keywords: Rashba band splitting; defect tolerance; ferroelectric domains; methylammonium lead iodide; photon recycling; polaron formation; slow recombination process.