Structural signature in Stokes-shifted broad emission of solution-processed hybrid lead perovskites

Understanding the emission process of Stokes-shifted broad photoluminescence (PL) in HOIPs is important for both fundamental science and applications. We present here results of temperature-dependent PL, X-ray diffraction, and Raman studies of solution-processed (BA)2PbCl4 flakes and powder prepared from these flakes to unveil the structural signature of the self-trapped exciton mechanism that explains the observed Stokes shift of broad PL in HOIPs. We also present sharp and intense PL spectra obtained from nanofilms of Lead-Formate perovskites prepared from the Langmuir monolayer of Stearic acid over solution of these flakes. A prominent position shift of broad PL peak and X-ray diffraction peak occurs only in 2D flakes as the temperature decreases, and laser-excitation intensity increases. Such redshift in PL peak position does not happen in 3D flake-powder. In 2D perovskite nanofilms, broad PL disappears as pseudo-halide Formate substitutes for Chlorine. Results on these three systems enable us to decipher the role of composition, dimensionality, and structure on the PL of HOIPs. Understanding the emission process of broad photoluminescence in hybrid organic-inorganic perovskites is crucial for advancing fundamental science and practical applications. Here, the authors use temperature-dependent photoluminescence, X-ray diffraction, and Raman studies of (butylammonium)₂PbCl₄ to reveal the structural mechanism for self-trapped excitons, highlighting the impact of composition, dimensionality, and structure on photoluminescence behavior.