Exploration of the origin of the excellent charge-carrier dynamics in Ruddlesden-Popper oxysulfide perovskite Y 2 Ti 2 O 5 S 2 .

Although the efficient separation of electron-hole (e-h) pairs is one of the most sought-after electronic characteristics of materials, due to thermally induced atomic motion and other factors, they do not remain separated during the carrier transport process, potentially leading to rapid carrier recombination. Here, we utilized real-time time-dependent density functional theory in combination with nonadiabatic molecular dynamics (NAMD) to explore the separated dynamic transport path within Ruddlesden-Popper oxysulfide perovskite Y 2 Ti 2 O 5 S 2 caused by the dielectric layer and phonon frequency difference. The underlying origin of the efficient overall water splitting in Y 2 Ti 2 O 5 S 2 is systematically explored. We report the existence of the bi-directional e-h separate-path transport, in which, the electrons transport in the Ti 2 O 5 layer and the holes diffuse in the rock-salt layer. This is in contrast to the conventional e-h separated distribution with a crowded transport channel, as observed in SrTiO 3 and hybrid perovskites. Such a unique feature finally results in a long carrier lifetime of 321 ns, larger than that in the SrTiO 3 perovskite (160 ns) with only one carrier transport channel. This work provides insights into the carrier transport in lead-free perovskites and yields a novel design strategy for next-generation functionalized optoelectronic devices.