Nonradiative Energy Transfer through Distributed Bands in Piezochemically Synthesized Cesium and Formamidinium Lead...

Repeated absorption of emitted photons, also called photon recycling, in large crystals and thick films of perovskites leads to delayed photoluminescence (PL) and decrease of PL intensity. The role of distinct band gaps, which act as donors and acceptors of energy, and nonradiative energy transfer on such delayed, low intensity emission is yet to be rationalized. Here we report delayed emission by nonradiative energy transfer across a distribution of energy states in close-packed crystallites of cesium lead bromide CsPbBr₃ , formamidinium lead bromide FAPbBr₃ , or the mixed halide FAPb(BrI)₃ perovskite synthesized in the form of thick pellets by the piezochemical method. The PL lifetime of the bromide-rich domain in the mixed halide pellet is considerably decreased when compared with a pure FAPbBr₃ pellet. Here the domains with higher bromide composition act as the energy donor, whereas the iodide-rich domains are the acceptors. Time-resolved PL measurements of CsPbBr₃ , FAPbBr₃ , and the mixed halide FAPb(BrI)₃ perovskite pellets help us to clarify the role of nonradiative energy transfer on photon recycling.