Ink formulation for organic photovoltaic active layers using non-halogenated main solvent for blade coating process

Abstract

Large area processing of organic photovoltaic cells and modules is a key step towards commercialization. At the same time, the scale-up of fabrication entails careful evaluation and selection of solvents, and optimization of processing parameters. It has been proven that using proper processing additives in polymer:PCBM bulk-heterojunction solution is one of the most effective strategies to improve the performance of organic photovoltaic cells. Here we report a new transition solvent strategy of using non-halogenated solvents to fabricate PDTSTPD: PC71BM based active layers. This strategy uses a combination of miscible good main solvent such as 1,2,4-trimethylbenzene and coadditives such as diphenyl ether (DPE) and 1-methylnaphtalene (MeN) for middle molecular weight PDTSTPD, or 1,8-diiodooctane (DIO) and MeN for high molecular weight PDTSTPD to tune the nano-scale morphology of the active layer during the film drying process. Inverted organic photovoltaic cells with an active area of 1cm2 on PET substrate fabricated by a blade coating process using the formulated ink have demonstrated a power conversion efficiency up to 5 %.