Publication date: 17th July 2025
We present a comprehensive study of MAPbBr₃ single crystals that combines steady-state photoluminescence (SSPL) and time-resolved photoluminescence (TRPL) over a wide temperature range (77–290 K).
The goal is to clarify the nature of the photoexcited species and the competition between radiative mechanisms in a system designed to minimize the influence of material defects. In a high-quality single crystal, the low-temperature orthorhombic phase reveals the coexistence of two spectrally and dynamically distinguishable channels: a near–band-edge excitonic emission and a lower-energy band attributable to radiative recombination mediated by surface defect states.
Temperature-dependent steady-state measurements further allow us to disentangle the impact of crystalline phases and electron–phonon coupling. The variation of peak energy and spectral broadening with temperature confirms dominant coupling to optical phonons. Interaction which LO phonons is also identified as the main intrinsic limit to mobility. This spectroscopic fingerprint is consistent with the general picture observed in hybrid perovskites[1,2]. Discontinuities in energy and linewidth around 150 K and 240 K mark the orthorhombic↔tetragonal and tetragonal↔cubic transitions, indicating a reconfiguration of the electronic landscape and of the defect states that govern recombination in each phase[3].
In the time domain, PL decays are analyzed using a diffusion model that yields the temperature dependence of the diffusion coefficient (D) and the surface recombination velocity (S)[4]. In the orthorhombic phase we document an abrupt increase in both D and S, consistent with a regime of weakly bound, highly mobile excitons with reduced phonon scattering. The long decay tails indicate that late-time dynamics are dominated by bulk diffusion.
Taken together, we show that excitons act as sensitive probes of structural order/disorder: their energies, linewidths, temporal dynamics and phonon coupling are affected by phase transitions. This temperature-dependent SSPL/TRPL approach provides a coherent map of the recombination channels in MAPbBr₃.
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