Fluorescent variations during the phase conversion of Cs–Pb–Br compounds

The lead halide perovskite is chemical unstable toward water or other polar solvents because of its ionic nature, which hinders the applications in high-performance and reliable devices. One of the main instabilities is phase conversion among different dimensions of Cs–Pb–Br compounds. In this work, hydration induced phase conversion of Cs–Pb–Br compounds is investigated. There are two anomalous fluorescent variations during the phase conversion: (1) the hydration-induced fluorescence quenching is irreversible; (2) the conversion from Cs 4 PbBr 6 to CsPbBr 3 leads to the weakening of green fluorescence. With our study, we found out: first, the hydration-induced conversion is mainly caused by the precipitation of CsBr. The extracted CsBr is spatially separated from the Cs–Pb–Br compounds, thus breaking the back conversion from CsPbBr 3 to Cs 4 PbBr 6 ; second, for the as-prepared Cs–Pb–Br compounds, the CsPbBr 3 nanodomains are well passivated by wide bandgap Cs 4 PbBr 6 , thus exhibiting a strong green emission. Whereas, after hydration, the passivation by Cs 4 PbBr 6 disappears and a large number of defects and traps appear. Consequently, the green fluorescence intensity decreases although the content of CsPbBr 3 increases.