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

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 C71-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 cm2) 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 cm2) 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.