Conformational control of morphology for perylene diimide dimer as electron transporting material at perovskite surface

Synthesis of core-twisted perylene diimide (PDI) dimers attached with thiophene linkers (PDI-NHR-Th(1-4)) and their electron transporting ability at perovskite surface were studied. Synthesized dyes showed a high-lying lowest unoccupied molecular orbital (LUMO) energy levels between -3.68 and -3.71 eV, which were compatible with the conduction band of CH3NH3PbI2Br (-3.60 eV). Herein, we have investigated the role of the different substituted positions of PDI monomers to thiophene linkage from its (2,5)-, (3,4)-, (2,4)-, or (2,3)-positions in modulating the morphology of PDI dimer, aggregation behavior for charge transfer properties, optical shifts in ground and excited states, and recombination resistances at the interfaces of p-i-n devices. Conformational changes of PDI dimers attaching to different positions of thiophene linkers are found to affect not only photo-pysical dynamics of excited states of the dyes, but also charge transport kinetics at the perovskite interfaces, changing the photovoltaic performance.