Efficient, large area organic photovoltaic modules with active layers processed with non-halogenated solvents in air

Abstract

Organic photovoltaic (OPV) modules with excellent power conversion efficiencies of 4.20% and 5.87% were obtained with blends of novel low bandgap polymers, POD2T-DTBT and PDTBT-alt-TT, respectively, with PCBM as the active layers. Large area polymer:PCBM blend films were deposited by blade coating with high film uniformity, fast processing speed, and low material consumption, without the need for an inert atmosphere. With the requirements of future manufacturing in mind, the effects of air exposure on the active layers and the substitution of chlorinated solvents for polymer processing were investigated. While the decline of Voc due to air exposure was recovered by appropriate treatment of the completed devices, FF and Jsc were significantly affected due to interfacial effects, indicating that air exposure should be limited in duration. Active layers of POD2T-DTBT:PCBM processed with less toxic, non-halogenated mixed solvents, comprising non-polar o-xylene with small amounts of polar additive, showed a fine, interpenetrating nanofibrous network that facilitates charge transport in bulk heterojunction photovoltaic cells. The performance of POD2T-DTBT:PCBM photovoltaic cells and modules processed with the new ink formulations were on par with that obtained with chlorinated solvents, with the modules exhibiting impressive power conversion efficiencies above 4%. The results indicated that POD2T-DTBT was an outstanding candidate for future OPV production due to its high performance, processibility in different ink formulations and compatibility with the large area coating techniques.