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 band gap two-dimensional-conjugated copolymers J61 and J71 with varied side chains were utilized as donors to construct efficient all-PSCs with the typical electron-withdrawing polymer N2200 as an acceptor. Eventually, moderate photovoltaic performance was obtained for the J61:N2200 device with a 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 devices. In addition, relatively weak thickness dependence of photovoltaic property and excellent long-term device stabilities (in N₂ and air, respectively) were observed for the J71:N2200 all-PSCs. These results reveal that J71 with trialkylsilyl side chains is a promising polymer donor candidate for developing high-performance all-PSCs for future practical applications.