Real-Time Monitoring of Progressive Crystal Phase Transformations and Associated Multi-Phase Optical Exciton Dynamics in Mixed (2D/3D) Inorganic–Organic Hybrid Semiconductors

Abstract

The unique crystal structure dimensionality, possibilities of a wide range of crystal phases, wide bandgap tunability, associated optical exciton characteristics, and eventual optoelectronic properties make inorganic–organic (IO) hybrid semiconductors fascinating optoelectronic materials. In this study, we investigate the digitized intercalation process of various organic moieties, resulting in a mixed IO hybrid system of type (R-NH3)2(R′-NH3)n–1PbnI3n+1 between (R-NH3)2PbI4 (2D, n = 1) to (R′-NH3)­PbI3 (3D, n = ∞) and vice versa. By employing real-time photoluminescence (PL) monitoring, we observe progressive and dynamic structural deviations/evolution and elucidate the underlying mechanisms occurring during the intercalation process. The interplay of (i) cyclic, (ii) long alkyl chain, and (iii) small alkyl amine based organic moieties during the intercalation leads to the formation of either 2D ((R-NH3)2PbI4) or 3D (R′-NH3PbI3) IO hybrid networks and unveiling significant structural phase variations within the 2D and 3D crystal packings. Several metastable interdigitized structural conformations appear during the dynamic process, ranging from n = 1 (2D) to n = ∞ (3D). Although, such metastable intermediate phases have been reported individually in chemically synthesized mixed IO hybrid structures, but in this work, for the first time, we demonstrate the real-time dynamic variations in these mixed IO hybrid configurations. The results have convincingly unveiled such conversions, which are clearly revealed by the progressive shift of exciton energies from high to low energies or vice versa. This comprehensive study provides a deep insight into various scenarios applicable to the nature of multiphase crystal packings in the broad range of IO hybrid semiconductors.