Manipulating the donor/acceptor (D/A) weight ratio is a critical route to produce highly efficient polymer solar cells (PSCs). However, most of the reported device performances are strongly sensitive to the blend ratio. In this work, highly efficient all-PSCs based on PBDB-T:N2200 active layer have been achieved, presenting impressive photovoltaic performance with high tolerance to wide D/A ratios ranging from 1:1 to 9:1, thus providing a broad blend ratio processing window for future practical production. In particular, the optimal device delivers the champion power conversion efficiency (PCE) of 8.61% with an outstanding fill factor (FF) of up to 75.4%, which is one of the highest FF values for the reported binary all-PSCs. Comprehensive morphological, electrical, and mechanism analysis together pointed out that the remarkable device performance are derived from the favorable interpenetrating network morphology, efficient exciton generation/dissociation, well-balanced carrier transport, and reduced bimolecular recombination. Moreover, compared to the small molecule-based and fullerene-based PSC counterparts, the all-PSCs demonstrate an excellent resilience to the D/A ratio, maintaining over 50% of the maximum PCE at a ratio of 49:1 with an extremely low acceptor content. These results depict a bright prospect of the developed all-PSCs for promising applications as flexible and scalable optoelectronic devices.
Keywords: all-polymer solar cells; blend ratio; charge transport; fill factor; morphology.