Compatible Acceptors Mediate Morphology and Charge Generation, Transpration, Extraction, and Energy Loss in Efficient Ternary Polymer Solar Cells

Ternary bulk-heterojunction (BHJ) polymer solar cells (PSCs) have been proved to show superior performance over binary BHJ PSCs. In this concise contribution, an octyl-substituted indacenodithieno[3,2-b] thiophene-based non-fullerene acceptor (O-ITIC), which is a derivative of ITIC but presents lower electron affinity, narrower optical band gap, and improved propensity to crystallize, is incorporated as a third component in the state-of-the-art PM6:Y6 binary BHJ blends to fabricate ternary BHJ solar cells. Results show that the optimized PM6:Y6:O-ITIC-based ternary BHJ solar cells reach higher power conversion efficiency (PCE) of 16.5% than that achieved in PM6:Y6- and PM6:O-ITIC-based binary solar cells with PCEs of 15.8 and 11.1%, respectively. Well-mixed acceptors phases and crystallite with a favorable face-on orientation are concurrently formed in the optimized ternary BHJ films. Consequently, more efficient exciton dissociation, improved and balanced charge transportation and extraction, and suppressed charge recombination losses occur in the optimized ternary BHJ devices with the aid of the third component O-ITIC. As a result, the optimized ternary devices demonstrate the lowest energy loss of 0.51 eV, an improved fill factor of 74.7%, and thus the highest PCE of 16.5%. This systematic study makes clear that rationally designed guest acceptors not only can provide additional channels for photon absorption and exciton dissociation but also can offer an effective strategy in tailoring the BHJ nanoscale morphology that are prerequisites for fast charge transportation, efficient charge extraction, and thus promising polymer solar cells.

Automated summary

By incorporating a non-fullerene acceptor with lower electron affinity, narrower band gap, and improved propensity to crystallize as a third component in binary BHJ blends, ternary BHJ solar cells with higher efficiency were achieved. The optimized ternary BHJ films exhibited well-mixed acceptors phases and crystallite with favorable orientation, leading to more efficient exciton dissociation and improved charge transportation. The third component O-ITIC aided in reducing energy loss, increasing fill factor, and achieving the highest PCE of 16.5% in the optimized ternary devices.