Size- and Composition-Dependent Exciton Spin Relaxation in Lead Halide Perovskite Quantum Dots

The strong spin–orbital coupling in lead halide perovskites allows for facile spin injection for spintronics applications, but on the other hand, it also limits the lifetime of the injected spins. Full-dimensional confinement of the carriers using quantum dots (QDs) has been envisioned as an effective means to prolong the spin relaxation lifetime and has been explored for II–VI and III–V group QDs. Here we applied this idea to colloidal lead halide perovskite QDs and measured the exciton spin dynamics of QDs of varying sizes and compositions using circularly polarized transient absorption spectroscopy at room temperature. Interestingly, the spin lifetimes of CsPbI₃ and CsPbBr₃ QDs were prolonged and shortened, respectively, as compared to those of their bulk counterparts. Both CsPbI₃ and CsPbBr₃ QDs showed decreasing spin lifetime with decreasing QD size. Possible spin relaxation mechanisms, including those that are unique to these quantum-confined systems, were proposed, with important ramifications for the use of these perovskite QDs in spin-related applications.