Mechanistic insights into excitonic photoluminescence in hybrid organic–inorganic perovskites with targeted regulation of organic cations

We report a mechanistic study of excitonic photoluminescence in predesigned hybrid organic–inorganic perovskite (HOIP) systems, i.e., (DMAEA)Pb2I6, (DMAPA)PbI4, (DEAEA)Pb2I6, and (DEAPA)4Pb5I18, featuring targeted regulation of organic cations. Starting from the prototype DMAEA (i. e.,2-N,N-dimethylamino-l-ethylamine) for (DMAEA)Pb2I6, the other three HOIPs differ only in the extensions with CH2 group(s) at the “head” or/and “tail” of DMAEA that is an “alkylated ammonia”. Their crystal structures are constructed and structural distortions are evaluated. The steady-state/transient absorption and emission spectroscopic characterizations, combined with the band-structure calculations, are conducted. The two different photoluminescence (PL) mechanisms are identified, i.e., PL emissions dominated by free excitons for (DMAPA)PbI4 and by self-trapped excitons for (DMAEA)Pb2I6, (DEAEA)Pb2I6, and (DEAPA)4Pb5I18. The self-trapped excitonic effect involved in the latter three HOIPs is quantitatively analyzed. This work would be of guiding value for the design of HOIP systems based on organic-cation engineering, beneficial for the pertinent performance optimization in light-emitting applications.