Large-area blade-coated organic solar cells processed from halogen-free solvent

Abstract

High performance organic solar cells (OSCs) are generally prepared by halogenated solvents, which are detrimental to the environment and human health. The replacement of hazardous halogenated solvents is a priority in the commercialization of solution-processed OSCs. In this study, poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl) benzo [1,2-b;4,5-b'] dithiophene-2,6-diyl-alt-(4- (2-ethylhexyl)-3-fluorothieno [3,4-b] thiophene-)-2-carboxylate-2-6-diyl)] (PBDTTT-EFT):[6,6]-phenyl C-71 -butyric acid methyl ester (PC71BM)-based device processed with binary halogen-free solvents (toluene and N-methyl-2-pyrrolidone) is fabricated by blade-coating method. Through the combination of morphological manipulation of active layer and interfacial engineering, the resulting OSCs deliver a promising power conversion efficiency (PCE) up to 11.09%. Importantly, large-area (216 cm(2)) blade-coated bulk-heterojunction OSCs is also demonstrated, and the resulting devices deliver a high PCE up to 5.03%, which is comparable to those of the devices processed with halogenated solvents (PCE = 5.20%). Additionally, the devices processed with halogen-free solvents also exhibit superior stability, maintaining 88% of its initial efficiency after 3960 h of continuous operation. More encouragingly, halogen-free solvents-based manufacturing process can also be performed under ambient conditions, and a moderate PCE of 3.67% is attained for large-area (216 cm(2)) OSCs. To the best of our knowledge, 3.67% represents the highest efficiency ever reported for air-processed large-area OSCs. This work paves the way towards the realization of environmentally-friendly large-area OSCs with high performance and long-term stability.