Temperature-Dependent Band Gap in Two-Dimensional Perovskites: Thermal Expansion Interaction and Electron–Phonon Interaction

Two-dimensional organic–inorganic perovskites have attracted considerable interest recently. Here, we present a systematic study of the temperature-dependent photoluminescence on phase pure (n-BA)2(MA)n−1PbnI3n+1 (n = 1–5) and (iso-BA)2(MA)n−1PbnI3n+1 (n = 1–3) microplates obtained by mechanical exfoliation. The photoluminescence peak position gradually changes from a red-shift for n = 1 to a blue-shift for n = 5 with an increase in temperature in the (n-BA)2(MA)n−1PbnI3n+1 (n = 1–5) series, while only a monotonous blue-shift has been observed for the (iso-BA)2(MA)n−1PbnI3n+1 (n = 1–3) series, which can be attributed to the competition between the thermal expansion interaction and electron–phonon interaction. In the (n-BA)2(MA)n−1PbnI3n+1 (n = 1–5) series, the thermal expansion interaction and electron–phonon interaction are both gradually enhanced and the former progressively dominates the latter from n = 1 to n = 5, resulting in the band gap versus temperature changing from a red-shift to a blue-shift. In contrast, both of these factors show a weaker layer thickness dependence, leading to the monotonous blue-shift in the (iso-BA)2(MA)n−1PbnI3n+1 (n = 1–3) series.