Bicomponent-random Approach to Synthesis of Donor Polymers for Efficient All-Polymer Solar Cells Processed from A Green Solvent

摘要： All-polymer solar cells (all-PSCs) can offer unique merits of high morphological stability to thermal and mechanical stress. To realize its full potential as flexible or wearable devices, it is highly desirable that the all-PSCs can be fabricated from green solvent with simple post-treatment to avoid thermal annealing on flexible substrate. This proposed a severely challenge on material design to tune their properties with suitable solubility, aggregation, and morphology. To address this challenge, here, a simple bicomponent-random approach on a D-A-type polymer donor was developed by just varying the D-A molar ratio. Under this approach, a series of new random polymers PBDTa-TPDb with different molar ratio of D component of 2D-benzo[1,2-b:4,5-b']dithiophene (BDT) and A component of thieno[3,4-c]pyrrole-4,6-dione (TPD) were designed and synthesized. The energy levels, light absorption, solubility and packing structure of random donors PBDTa-TPDb were found to vary substantially with the various D-A molar ratio. The devices based PBDTa-TPDb/P(NDI2HD-T) were fabricated to explore the synergistic effects of processing solvent and composition of D-A-type random polymers. The results show that nanoscale morphology, balanced miscibility/crystallinity of blend and photovoltaic properties could be rationally optimized by tuning the composition of random donors. As a result, as-cast all-PSC based optimal donor PBDT5-TPD4 achieves a best power conversion efficiency (PCE) of 8.20% processed from green solvent, which performs better than that based reference polymer (PCE: 6.41%). This efficiency is the highest value for all-PSCs from BDT-TPD-based donors. Moreover, the optimized devices exhibited relatively insensitive to the thickness of the active layer and good stability.