Additive and High-Temperature Processing Boost the Photovoltaic Performance of Nonfullerene Organic Solar Cells Fabricated with Blade Coating and Nonhalogenated Solvents

Benefitting from narrow band gap nonfullerene acceptors, continually increasing power conversion efficiency (PCE) endows organic solar cells (OSCs) with great potential for commercial application. Fabricating high-performance OSCs with potential for large-scale coating and nonhalogenated solvent processing is a necessity. Herein, we have proposed the use of nonhalogenated solvents combined with high-temperature blade coating to prepare a PM6 (poly[(2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione)]):Y6 (2,2′-((2Z,2′Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2″,3′′:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2-g]thieno[2′,3′:4,5]thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene)))blend active layer. The resultant OSCs deliver a PCE of 15.51% when the PM6:Y6 active layer is blade-coated at 90 °C in nonhalogenated o-xylene (o-XY) host solvent containing 1,2-dimethylnaphthalene (DMN) additive. It is found that high-temperature blade coating and nonhalogenated solvent additive DMN can suppress excessive aggregation of Y6 and enhance the crystallinity of PM6 and Y6 by regulating the dynamic process of active layer formation. Finally, an optimized blend morphology with nanofibrous phase separation and enhanced crystallinity are achieved for the PM6:Y6 active layer prepared with high-temperature blade coating and nonhalogenated o-XY:DMN solvents, which not only shortens the film-drying time but also leads to increased charge generation, transport, and collection efficiency. The 1.00 cm2 OSCs prepared with high-temperature blade coating and nonhalogenated solvents exhibit a high PCE of 13.87%. This approach shows great potential for large-area fabrication of OSCs.