Multiscale Molecular Simulation of Nanomorphologies of Bulk Heterojunction Polymer Solar Cells

Bulk heterojunction (BHJ) organic photovoltaic cells (OPVs) are one of the promising sources for low-cost solar energy harvesting. In addition to their low production costs, BHJ OPVs also have superior mechanical flexibility and light-weight over their silicon-based counterparts. The key toward device performance of BHJ OPV is the nanomorphology of the BHJ layer - the photoactive layer of OPV comprising an interpenetrating network of electron donor and acceptor materials domains. When incident photons are absorbed by the electron donor materials, excitons (bounded electron/hole pairs) are formed; these excitons then diffuse to the donor/acceptor interface and dissociate into free electrons/holes to transport to their respective electrodes for photocurrent generation. The BHJ nanomorphologies are extremely sensitive to their corresponding device fabrication protocols; hence, comprehensive insights into the correlations between device fabrication protocols and resulting BHJ nanomorphologies are critical for nanomorphology control to promote BHJ OPV device performance. Nevertheless, the experimental characterizations of BHJ nanomorphologies are never trivial; therefore, computer experiments may provide BHJ morphological details that are still elusive from experimental perspectives to fill the missing puzzle.

The typical length scale in experimental characterization of BHJ morphology is of the order of several tens of nanometers, which is well beyond the reach of ab initio calculations and all-atom molecular dynamics (MD) simulations for investigating BHJ morphologies. Since I joined RCAS in November, 2009, I have devoted to developing a multiscale molecular simulation framework that can in silico evolve the nanomorphology of the BHJ layer of different donor/acceptor blends (polymer/fullerene, polymer/nanocrystal) under various fabrication protocols (e.g. thermal annealing, solvent evaporation), with system sizes compatible with those in experiments. With such multiscale molecular simulation framework, my group is able to reveal the multi-resolution morphological details of the BHJ layer that are not yet available from experiments. In this field I have published five papers - including two papers published in the Energy [IMAGE png] Environmental Science, and one book chapter (submitted to book editor).



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barbarossapao 2015-09-16