Abstract
Experimental studies suggest that the intermolecular interactions between polymers and fullerenes are critical to the design of efficient bulk heterojunction organic photovoltaic cells. However, a detailed understanding of these intermolecular interactions is still lacking. In this work, by correlating simulation data with experimentally determined efficiencies, we identify interfacial factors that can be used to enhance the performance of BHJ organic solar cells (OSCs). We employ dispersion corrected density functional theory method (B97D3) to investigate the properties of the interfacial region in various promising combinations of monomers (P3HT, PTB7, PCDTBT, PBDTTPD, PNT4T, PffBT4T, and PBTff4T) and fullerenes (PCBM and PC71BM) used in OSCs. We analyze the conformational structures and binding energies of these combinations, and obtain the electronic offsets of gas phase and interacting monomers and fullerenes. Our findings indicate that monomer/fullerene pairs that exhibit the highest experimentally determined PCEs (i.e. those containing PNT4T, Pff4TBT, and PBTff4T) have the following common characteristics: the lowest interfacial LUMO offset, the largest ratio of Voc (as determined by interfacial band gap) to monomer's energy gap, Eg, and a relatively high binding energy. We believe that selecting materials with these interfacial properties will lead to a development of OSCs with higher efficiencies.
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•Correlations between properties of polymers and efficiencies of organic solar cells are studied.•In most stable conformations, polymers should be placed on the side of fullerenes.•The lowest LUMO offsets and the highest interfacial band gaps per monomer's energy gap correlate well with efficiencies.