Highly Efficient Ternary All-Polymer Solar Cells with Enhanced Stability

Developing organic solar cells (OSCs) based on a ternary active layer is one of the most effective approaches to maximize light harvesting and improve their photovoltaic performance. However, this strategy meets very limited success in all-polymer solar cells (all-PSCs) due to the scarcity of narrow bandgap polymer acceptors and the challenge of morphology optimization. In fact, the power conversion efficiencies (PCEs) of ternary all-PSCs even lag behind binary all-PSCs. Herein, highly efficient ternary all-PSCs are realized based on an ultranarrow bandgap (ultra-NBG) polymer acceptor DCNBT-TPC, a medium bandgap polymer donor PTB7-Th, and a wide bandgap polymer donor PBDB-T. The optimized ternary all-PSCs yield an excellent PCE of 12.1% with a remarkable short-circuit current density of 21.9 mA cm⁻². In fact, this PCE is the highest value reported for ternary all-PSCs and is much higher than those of the corresponding binary all-PSCs. Moreover, the optimized ternary all-PSCs show a photostability with ≈68% of the initial PCE retained after 400 h illumination, which is more stable than the binary all-PSCs. This work demonstrates that the utilization of a ternary all-polymer system based on ultra-NBG polymer acceptor blended with compatible polymer donors is an effective strategy to advance the field of all-PSCs.