Organic Solar Cells with Large Insensitivity to Donor Polymer Molar Mass across All Acceptor Classes

Abstract

Donor polymer number-average molar mass (M_n) has long been known to influence organic photovoltaic (OPV) performance via changes in both the polymer properties and the resulting bulk heterojunction morphology. The exact nature of these M_n effects varies from system to system, although there is generally some intermediate M_n that results in optimal performance. Interestingly, our earlier work with the difluorobenzotriazole (FTAZ)-based donor polymer, paired with either N2200 (polymer acceptor) or PC₆₁BM (fullerene acceptor), demonstrated <10% variation in power conversion efficiency and a consistent morphology over a large span of M_n (30 kg/mol to over 100 kg/mol). Would such insensitivity to polymer M_n still hold true when prevailing small molecular acceptors were used with FTAZ? To answer this question, we explored the impact of FTAZ M_n on OPVs with ITIC, a high-performance small-molecule fused-ring electron acceptor (FREA). By probing the photovoltaic characteristics of the resulting OPVs, we show that a similar FTAZ M_n insensitivity is also found in the FTAZ:ITIC system. This study highlights a single-donor polymer which, when paired with an archetypal fullerene, polymer, and FREA, results in systems that are largely insensitive to donor M_n. Our results may have implications in polymer batch-to-batch reproducibility, in particular, relaxing the need for tight M_n control during synthesis.

Citation

Organic Solar Cells with Large Insensitivity to Donor Polymer Molar Mass across All Acceptor Classes
Stephanie Samson, Jeromy Rech, Lorena Perdigón-Toro, Zhengxing Peng, Safa Shoaee, Harald Ade, Dieter Neher, Martin Stolterfoht, and Wei You
ACS Applied Polymer Materials 2020 2 (11), 5300-5308
DOI: 10.1021/acsapm.0c01041