Investigation Of Supramolecular Interactions Between Liquid Crystals And Accepter For Improved Morphological Stability In Solar Cells

Organic solar cells have attracted a lot of attentions due to its light weight, large area roll to roll production. In order to realize commercialization, two challenges including low power conversion efficiency(PCE) and instability must be overcome. To optimize the active layer morphology is an important way to improve the PCE and stability, which could be realized through incorporation of an additive into the active layer.In this article, the supramolecular interactions between liquid crystals(LCs) of different chemical structure and PCBM molecules have been studied, showing that the LCs containing electron-withdrawing CN substituent on the phenyl ring exhibited the strongest interactions with PCBM, as revealed by theoretical calculations and experimental analysis based on fourier transform infrared spectrometer(FTIR), differential scanning caloremetry(DSC), polarized optical microscope(POM). After the electric field treatment at 600 V/mm in air environment, the P3HT:PCBM containing 4-octyloxy-4’-cyanobiphenyls(8OCB) showed of higher power conversion efficiency(PCE) of 2.9 % and more stable morphology, in contrast to the specimen containing dioctylterthiophene(8TTP8) with PCE of 2.7 %. The 4-cyano-4’-pentylterphenyl(5CT) was found to restrict crystallization of PC61 BM molecules in P3HT:PC61BM system after annealing at 150 °C for 1 h, due to the strongest strength of supramolecular interactions. The supramolecular interaction between liquid crystals and PCBM could also improve the morphological stability in PTB7-Th:PC71BM system, by maintaining the PCE of 3.5 % after annealing at 150 °C for 10 min in air as compared with that of 2.0 % without 5CT.