Temperature-dependent photoluminescence of CsPbX₃ nanocrystal films

Temperature-dependent photoluminescence (PL) properties of all-inorganic perovskite CsPbX₃ (X=Cl, Br, I, or their mixtures) nanocrystal (NC) films are studied by use of steady-state and time-resolved PL spectroscopies. It is confirmed that the PL intensity of the NC films decreases rapidly with increasing temperature below 300 K and is nearly invariant till 370 K due to thermal quenching and degradation, respectively. With increasing temperature, photo energies of linewidth and emission peak become larger due to stronger exciton-phonon coupling. It is found that temperature-dependent PL is composed of a band-edge excitonic state and trapping state emission and produces the observation of biexponential kinetics. The short-lived emission is due to band-edge exciton recombination, while the component with long-lived lifetime is ascribed to trapping state, which arises from recombination in NC that has a photoinduced trapped pathway and a temporally resolved peak shift. Besides organic-inorganic perovskite hybrid NCs, trapping state also exists in all-inorganic CsPbX₃ NCs, even though PL spectrum has high PL quantum yield and narrow emission linewidths.