Fast Polaron Formation and Low Carrier Mobility in Defect-Free Polyhedral CsPbBr3 Perovskite Nanocrystals

Albeit enormous achievement has already been made in photovoltaic and optoelectronic fields with perovskites, further advancement is needed to address key challenges encountered in these systems. Here, we synthesized polyhedral dodecahedron cesium lead bromide (dodecahedron-CsPbBr3) perovskite, which offers new polar facets exposed on the surface, longer carrier lifetime, and high photoluminescence (PL) quantum yield. PL investigation conducted at cryogenic temperature for dodecahedron-CsPbBr3 is clearly indicative of the absence of bound excitons originating from shallow traps, which otherwise are prevalent in conventional CsPbBr3 nanocubes (cube). The prolonged carrier cooling and 20–30% enhanced biexciton yield from transient absorption (TA) studies can be directly correlated with rapid polaron formation (0.25 ps) and defect-free nature of dodecahedron-CsPbBr3. Furthermore, temperature-dependent TA studies illustrate accelerated carrier cooling as the lattice temperature is lowered up to 5 K, which is related to the incapability of the lattice to support polarons. Terahertz (THz) spectroscopic measurements reflect lower carrier mobility in dodecahedron-CsPbBr3 than that in cube-CsPbBr3, validating the claim of slower carrier cooling as demonstrated by TA studies. These findings make dodecahedron-CsPbBr3 a potential contender for advanced next-generation efficient optoelectronic devices.