Abstract
We present molecular dynamics simulations of a ternary blend of P3HT, PCBM and P3HT-grafted silica nanoparticles (SiNP) for applications in polymer-based solar cells. Using coarse-grained models, we study the effect of SiNP on the spatial arrangement of PCBM in P3HT. Our results suggest that addition of SiNP not only alters the morphology of PCBM clusters but also improves the crystallinity of P3HT. We exploit the property of grafted SiNP to self-assemble into a variety of anisotropic structures and the tendency of PCBM to preferentially adhere to SiNP surface, due to favorable interactions, to achieve morphologies with desirable characteristics for the active layer, including domain size, crystallinity of P3HT, and elimination of isolated islands of PCBM. As the concentration of SiNP increases, the number of isolated PCBM molecules decreases, which in turn improves the crystallinity of P3HT domains. We also observe that by tuning the grafting parameters of SiNP, it is possible to achieve structures ranging from cylindrical to sheets to highly interconnected network of strings. The changes brought about by addition of SiNP shows a promising potential to improve the performance of these materials when used as active layers in organic photovoltaics.
Highlights
Using molecular dynamics simulations we study the effect of P3HT-grafted silica nanoparticles (SiNP) on the morphology of phenyl-C61-butyric acid methyl ester (PCBM) in P3HT for polymer-based solar cell applications
Addition of grafted SiNP drastically improves the morphology of P3HT-PCBM blends
We study the effect of SiNP on certain properties that are crucial for improving the efficiency of solar cells
Summary
Several theoretical[20,21,22,23,24,25] and experimental[26,27,28,29,30,31,32] studies exist that focus on improving the spatial arrangement of polymers and nanoparticles in bulk[21,24,31] and in films[26,32,33,34]. Adding an inert polymer like polystyrene to the P3HT-PCBM blend results in the formation of highly ordered columnar structures due to lateral phase separation in thin films[32]. This structure provides high interfacial area for charge transport but lowers the crystallinity of PCBM. In most of the work cited above, especially where a third component is added to the existing P3HT-PCBM blend, certain advantages are observed, the efficiency of such cells show no significant improvement This is because the efficiency of polymer-based solar cells depends on various factors and achieving a thorough control over all of them is extremely challenging. In addition to improving the overall structure of PCBM domain, we note that addition of SiNP reduces the number of isolated PCBM particles within the blend and improves the crystallinity of P3HT domains
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