Performance enhancement of polymer-based solar cells by induced phase-separation with silica particles

Abstract

Adding metallic nanoparticles into bulk-heterojunction, polymer-based solar cells has been proven an effective strategy to enhance light absorption of the active layer and device performance. However, the high-energy surfaces on the nanoparticles may also affect the morphology of the active layer by influencing phase-separation, which has not been studied in detail. Here, we show that silica particles embedded in the active layer will affect the aggregation behavior of [6,6]-phenyl C₆₁-butyric acid methyl ester (PCBM) in the bulk-heterojunction of poly(3-hexylthiophene) (P3HT):PCBM. Using a novel graphical technique to analyze the absolute scattering intensity of small angle neutron scattering data, we conclusively demonstrate that some PCBM will migrate away from the bulk solution to the surface of the silica upon annealing and improve the device performance. The overall effect is to decrease the device series resistance and improve the power conversion efficiency by 10 to 20% relative to the control group. In contrast to metallic nanoparticles that utilize the surface plasmon resonance, our results indicate that, even with optically inert particles, the induced phase separation of PCBM may also result in an improved device.