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 photopysical dynamics of excited states of the dyes, but also charge transport kinetics at the perovskite interfaces, changing the photovoltaic performance.