Temperature-Dependent Photoluminescence and Carrier Dynamics of CsPbBr3 Quantum Dots: Ligand-Mediated Electron-Phonon Coupling and Trap State Energetics in Solution versus Film

• • Electron-phonon coupling in solution is ~2× stronger than in film, with average phonon energies of ~38 meV (OPA) and ~32 meV (TPA) in solution versus ~22 meV (OPA) and ~16 meV (TPA) in film; this disparity directly implicates ligand phonons in solution-phase recombination and warns that film fabrication protocols must account for ligand loss to avoid unpredictable thermal quenching in devices. • • Room-temperature PL lifetimes are 22.5 ns for solution and 5 ns for film, a 4.5× reduction upon film formation; both lifetimes increase with temperature, indicating thermally activated trap-state carrier release that dominates non-radiative decay at low temperatures and imposes a fundamental efficiency ceiling on QD-LEDs operating below 300 K. • • Trap energy levels are ~20 meV in film versus ~4 meV in solution, a 5× deepening that correlates with exciton localization and reduced wavefunction overlap with ligand phonons; this deeper trap distribution in films accelerates non-radiative recombination and explains the spectral red-shift and linewidth broadening commonly observed in QD films. • • The frozen-solution control shows no significant deviation from room-temperature solution behavior, ruling out solvent dynamics as the primary driver and isolating ligand-ligand interactions during film formation as the mechanism for increased trap density and reduced electron-phonon coupling; this identifies ligand engineering—rather than solvent selection—as the primary lever for trap passivation in solid-state devices.