(193g) Improved Performance of Polymer Solar Cells By Silica Nanoparticles

We have found an improvement in the performance of polymer-based solar cells by filling the bulk-heterojunction active layer consisting of polymer and fullerene with 133 nm diameter silica nanoparticles. These silica particles are electrical insulators and weak light scatters in the visible spectra due to their small sizes and similar refractive index to the polymer and fullerene. With a particle volume fraction of about 10% in the active layers, the performance of the devices was not hurt but instead slightly improved. In the devices made with regioregular poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM), the improvement was evident across a wide range of mixing ratios between PCBM and P3HT. In particular, the power conversion efficiency at AM 1.5G spectrum was increased from 2.75±0.06% to 3.35±0.17% in the device with 60% of PCBM by weight. The improvement mainly comes from the larger fill factors, indicating enhanced charge transport properties in the active layer. We investigated the mechanism of the improvement by using small angle neutron scattering and other microscopy techniques. This study suggests that when nanoparticles are implemented into the active layer, their physical presence and its influence on the structure of the bulk-heterojunction should be considered in addition to other electrical and optical properties they possess.