Lee, Cheng-Kuang; Pao, Chun-Wei
Nanomorphology Evolution of P3HT/PCBM Blends during Solution-Processing from Coarse-Grained Molecular Simulations
JOURNAL OF PHYSICAL CHEMISTRY C, 118:11224-11233, MAY 29 2014

Solvent screening is a critical aspect of the nanomorphological control of low-cost, all-solution-processed bulk heterojunction organic photovoltaic cells. In order to reveal the correlations between solvent/solvent mixtures and the bulk heterojunction nanomorphologies during solution-processing, we constructed a multiscale, coarse-grained molecular simulation model for ternary solvent/P3HT/PCBM mixtures to systematically investigate the nanomorphologies of P3HT/PCBM blends during solution-processing in solutions over a wide range of P3HT/PCBM solubilities and solvent evaporation rates experienced during spin-casting processes. The resulting bulk heterojunction layer morphologies of the dried films were in good agreement with available experimental results from as-spun films, which validates our coarse-grained model. Our simulations indicated that the bulk heterojunction morphologies formed in solution involve a complicated interplay among the affinities of the solvent, P3HT, and PCBM in the ternary system, as well as the solubilities of the donor and acceptor; in particular, the solubility of the less-mobile material (i.e., P3HT) can notably affect the film quality, compactness, and the degree of donor/acceptor domain fineness in the dried films. Therefore, the present study demonstrates that this multiscale molecular simulation model can be used to accurately investigate the morphological evolution of bulk heterojunction blends during solution-processing and can be readily applied to the modeling of other advanced all-solution-processed organic photovoltaic cells such as small-molecule bulk heterojunction organic photovoltaic cells.

DOI:10.1021/jp501323p

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