Regulation of exciton behaviour in 2D perovskites via halogen doping
Two-dimensional metal halide perovskites (2D MHPs) exhibit strong excitonic effects and structural tunability, but their photoelectric properties are dictated by exciton dynamics. This study investigates halogen doping in PEA2Pb(Br1−xClx)4, revealing a systematic spectral evolution from blue to white-light emission as Cl content increases. Temperature-dependent photoluminescence and lattice distortion analysis indicate that Cl doping induces subtle structural perturbations, switching between extrinsic and intrinsic self-trapped exciton (STE) states. Below x = 0.2, intrinsic STE formation is enhanced via lattice softening; above x = 0.2, defect-assisted trapping pathways dominate. A dual-channel trapping model, validated by temperature-activated detrapping kinetics and transient absorption spectroscopy, accounts for the observed spectral broadening. These findings provide a defect engineering strategy for tailoring emission in low-dimensional hybrid perovskites, with implications for white-light LEDs and scintillators.