The Influence of Solvent Additive on Polymer Solar Cells Employing Fullerene and Non‐Fullerene Acceptors

Abstract Small‐molecule‐based non‐fullerene acceptors (NFAs) are emerging as a new field in organic photovoltaics, due to their structural versatility, the tunability of their energy levels, and their ease of synthesis. High‐efficiency polymer donors have been tested with these non‐fullerene acceptors in order to further boost the efficiency of organic solar cells. Most of the polymer:fullerene systems are optimized with solvent additives for high efficiency, while little attention has been paid to NFA‐based solar cells so far. In this report, the effect of the most common additive, 1,8‐diiodooctane (DIO), on PTB7‐Th:PC 71 BM solar cells is investigated and it is compared with non‐fullerene acceptor 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐ s ‐indaceno‐[1,2‐b:5,6b′]di‐thiophene (ITIC) devices. It is interesting that the high boiling solvent additive does have a negative impact on the power conversion efficiency when PTB7‐Th is blended with ITIC acceptor. The solar cell devices are studied in terms of their optical, photophysical, and morphological properties and find out that PTB7‐Th:ITIC devices with DIO results in coarser domains, reduced absorption strength, and slightly lower mobility, while DIO improves the absorption strength of the PTB7‐Th:PC 71 BM blend film and increase the aggregation of PC 71 BM in the blend, resulting in higher fill factor and J sc .