Insight into the Efficiency and Stability of All-Polymer Solar Cells Based on Two 2D-Conjugated Polymer Donors: Achieving High Fill Factor of 78%

Achieving high fill factor (FF) is a great challenge for the all polymer solar cells (all-PSCs) since the FF can be influenced by numerous complicated factors. In this work, two medium bandgap 2D-conjugated copolymers J61 and J71 with varied side chains were utilized as donor to construct efficient all-PSCs with the typical electron-withdrawing polymer N2200 as acceptor. Eventually, moderate photovoltaic performance was obtained for J61:N2200 device with power conversion efficiency (PCE) of 6.58% and FF of 60.18%. While the J71:N2200-based all-PSCs delivered an outstanding PCE of 9.31% with an unprecedented FF of 78.00%. To the best of our knowledge, such an FF of 78% represents a record value for binary all-PSCs systems, which demonstrates that the all-PSCs can realize excellent FF comparable to other PSCs systems. The favorable blends morphology, molecular orientation, balanced charge transport and suppressed recombination together contributed to the remarkable photovoltaic performance of J71:N2200 devi...