title: Fine tuning of the PCDTBT-OR:PC71BM blend nanoscale phase separation via selective solvent annealing toward high-performance polymer photovoltaics.
abstract: Solution-processable polymer solar cells show great promise for providing a cost-effective route to create lightweight and flexible solar energy conversion devices. The photoactive layer comprising the conjugated polymer donor and fullerene derivative acceptor must be optimized to form bicontinuous nanoscale phase separation in order for efficient exciton dissociation and charge collection due to the short exciton diffusion length of organic semiconductors. The donor polymer poly[9-(heptadecan-9-yl)-9H-carbazole- 2,7-diyl-alt-(5,6-bis(hexyloxy)-4,7-di(thiophen-2- yl)benzo[c][1,2,5]thiadiazole)-5,5-diyl] (PCDTBT-OR) has a deeper highest occupied molecular orbital level compared to its counterpart PCDTBT, and shows promise in increasing the open-circuit voltage and power conversion efficiency (PCE) of polymer solar cells. The phase separation evolution of the PCDTBT-OR:PC71BM blend with various weight ratios under tetrahydrofuran (THF) vapor annealing and its influence on the photovoltaic performance is investigated in detail. It is found that THF vapor annealing can promote the acceptor PC71BM aggregation from the donor PCDTBT-OR matrix to form nanoscale donor/acceptor phase separation for efficient exciton dissociation and charge collection depending on the donor/acceptor weight ratio and the annealing time. The THF vapor-annealed PCDTBT-OR:PC71BM solar cells exhibit remarkable enhancement, with a PCE of 7.01% compared to 3.25% of the as-cast solar cells with the same active layer thickness. This work provides a general methodology to construct nano-interpenetrating networks for homogeneous polymer/fullerene blends and is potentially applicable to the roll-to-roll manufacturing of polymer solar cells.
authors.affiliation: State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, People's Republic of China. University of Chinese Academy of Sciences, Beijing 100039, People's Republic of China.
authors.forename: Bin
authors.initials: B
authors.lastname: Meng
authors.forename: Gang
authors.initials: G
authors.lastname: Fang
authors.forename: Yingying
authors.initials: Y
authors.lastname: Fu
authors.forename: Zhiyuan
authors.initials: Z
authors.lastname: Xie
authors.forename: Lixiang
authors.initials: L
authors.lastname: Wang