Circularly Polarized Photoluminescence Obtained by Optical Spin Pumping in Achiral Lead-Halide Perovskites: Implications of Interface-Induced Rashba Splitting.

Spin-polarized electronic and optical properties in semiconductors are critical for potential spintronic device applications. However, such spin polarization is readily randomized by thermal fluctuations and generally observable only at low temperatures. By employing circularly polarized laser excitation for optical spin pumping, we detected circularly polarized emission from achiral two-dimensional/three-dimensional mixture films of (MBA)2PbBr4·(CsPbBr3)x (x = 0.5, 1, 1.5, 2, where x is the molar ratio). The circular polarization degree reaches 6%, exhibits a negative correlation with the x value, and is nearly insensitive to temperature variation. Moreover, these films display no circular dichroism absorption signals or circularly polarized luminescence upon excitation with a Xe lamp. We therefore conclude that strong Rashba-like splitting is enhanced in the interfacial regions around CsPbBr3 nanocrystals within the composite. Regulating the grain size may provide a new avenue for designing perovskite-based spintronic materials. More importantly, such spin polarization can be operating at room temperature.