Synthesis of cesium lead bromide nanoparticles by the ultrasonic bath method: A polar-solvent-free approach at room temperature.

Colloidal synthesis of CsPbBr nanoparticles (NPs) is often carried out by involving polar solvents that threaten the chemical stability of the NPs. Here, we report a polar-solvent-free synthesis of all-inorganic CsPbBr NPs by employing an ultrasonic bath approach. The phase evolution of the CsPbBr NPs strongly depended on the duration of ultrasonication. A secondary phase of CsPbBr was also found to evolve, which emitted narrow blue-emission bands. For the longest period of ultrasonication (12 h), the CsPbBr and CsPbBr phases co-existed to produce blue and green emission bands with a photoluminescence quantum yield (PLQY) of 53%. The purest form of CsPbBr phases was observed for the NPs produced by sonicating the precursors for 8 h. They exhibited narrow green emission bands with a PLQY of 50%. The power-conversion efficiency of a silicon solar cell was remarkably increased when coated with the CsPbBr NPs, thus, proving its potential to be used as a spectral downshifter for Si solar cells.