Dual Sensitizer and Processing-Aid Behavior of Donor Enables Efficient Ternary Organic Solar Cells

Herein, we report ternary organic solar cells with a power conversion efficiency (PCE) of 14.0%. By incorporating 10 wt % of BIT-4F-T in the PTB7-Th:IEICO-4F blend, we obtain an enhancement of all photovoltaic parameters compared to the binary devices, leading to a 15% performance improvement in ternary blend. The high photocurrent in 10% BIT-4F-T blend results from a complementary absorption profile of donor components and a hole transfer from BIT-4F-T to PTB7-Th. Morphological and device characterizations reveal that the addition of 10% BIT-4F-T acts not only as a sensitizer but also as a solid processing aid, which is beneficial for charge generation and transport. The effect of the third component is observed in different non-fullerene and fullerene OSCs. Our study demonstrates that careful selection of a third component, where dual sensitizing and processing-aid effects are observed, can be a design strategy to achieve a concomitant improvement in all photovoltaic parameters. The organic photovoltaics (OPV) landscape is nowadays facing a new era, ferried by the development of novel and stable acceptor materials, the so-called non-fullerene acceptors (NFAs), making the 15% power conversion efficiency (PCE) threshold no longer a research dream but a real goal. Despite the priority of high efficiency, the device longevity as well as the large area fabrication need to be addressed to make competitive organic solar cells with the other thin-film photovoltaic technologies. An elegant approach to overcome these limitations is the concept of ternary blend organic solar cells: three (or more) organic materials are combined from one hand to simultaneously enhance all photovoltaic parameters, which in turn will increase the power output of the solar cell. On the other hand, ternary blends have the potential to improve the device stability under light, thermal, and shelf-life conditions compared to traditional donor:acceptor blends. Here, we show ternary organic solar cells with a power conversion efficiency of 14%. By a careful selection of a third component (BIT-4F-T), we obtain an enhancement of all photovoltaic parameters compared to the binary devices (PTB7-Th:IEICO-4F). This is because of a dual effect of the third component acting not only as sensitizer but also as a solid processing aid, which is beneficial for charge generation and transport.