Ternary Strategy Enables Non‐Halogenated Solvent‐Processed All‐Polymer Solar Cells with High Efficiency Over 18%

Abstract Herein, efficient ternary all‐polymer solar cells (all‐PSCs) are fabricated by employing PDEDTQ that possesses down‐shifted highest occupied molecular orbital (HOMO) level and blue‐shifted absorption with higher maximum absorption coefficients compared with the host donor JD40‐BDD20 as a guest donor into the JD40‐BDD20:PA‐5 host blend. The enhanced light‐harvesting and the energy transfer from PDEDTQ to JD40‐BDD20 can be observed in the ternary device, which conduces to improving the short circuit current density (J_SC). Additionally, the PDEDTQ shows relatively weak crystalline and well miscibility with the JD40‐BDD20, meaning that the morphology can be tuned using the PDEDTQ. Subsequently, a more uniform and fine‐divided network with slightly weakened crystalline occurs in the ternary blend film, implying that a more intermixing domain with a higher density of donor/acceptor (D/A) interfaces may be formed. Thus, compared with JD40‐BDD20:PA‐5, the ternary device obtained enhanced exciton dissociation and charge extraction, reducing charge recombination and energy loss (E_loss). Ultimately, in addition to guaranteeing outstanding fill factor (FF), the higher J_SC and improve open circuit voltage (V_OC) are achieved and then boosted the power conversion efficiency (PCE) from 17.39% to 18.47%, which is one of the highest PCEs for the all‐PSCs. Overall, this work provides guidance on forming a high‐quality network with uniform distribution of D/A using ternary strategy, and then obtaining high‐efficiency all‐PSCs processed using non‐halogenated solvent.