Quantitative Decoupling of Recombination Kinetics in Compositionally and Interfacially Modified CsPbBr3/Cs4PbBr6 Films

Abstract Nonradiative defect-assisted recombination and radiative electron–hole recombination jointly determine the photoluminescence efficiency of metal halide perovskite films. However, the manner in which compositional and interfacial modifications affect these competing channels remains insufficiently quantified. Here, we analyze recombination dynamics in thermally evaporated CsPbBr3/Cs4PbBr6 composite films modified through Cs:Pb compositional regulation, KBr incorporation, and phenethylammonium iodide (PEAI) interfacial treatment. Temperature-dependent steady-state and time-resolved photoluminescence measurements from 77 to 298 K are used to estimate an effective first-order recombination rate constant (k1) and a calculated bimolecular radiative electron–hole recombination coefficient (k2). Relative to Sample 1 (Cs:Pb = 1:1), the room-temperature k1 of Sample 10 (3 nm C60/Cs:Pb = 1.4:1 (10 at% KBr)/3 nm PEAI) decreases from 334 × 106 to 13.2 × 106 s–1, corresponding to an approximately 25-fold reduction, while the apparent thermal activation energy derived from k1(T) decreases from 72.4 to 28.1 meV. The calculated k2 increases from 21.5 to 88.1 × 10–10 cm3 s–1, corresponding to an approximately 4.1-fold increase. The modified film also exhibits the highest photoluminescence quantum yield in the investigated series (43.2%), a higher effective thermal-quenching energy (79.9 meV), and lower inhomogeneous line width broadening (Γ0 = 18.9 meV). These results establish a quantitative relationship among defect-related recombination, radiative recombination, thermal-quenching behavior, and thin-film photoluminescence, while avoiding assignment of a single microscopic mechanism beyond the available evidence.