Facile transfer method for fabricating light-harvesting systems for polymer solar cells

In this study, we used a transferring process to fabricate a simple light-harvesting system featuring 2D periodic granular-like electrodes for polymer solar cells (PSCs). This transferring technique, which was based on nanosphere lithography, could be used to fabricate periodic nanostructures on both the photoactive layers and the Al electrodes in the normal PSC device configuration (indium tin oxide glass/PEDOT: PSS/photoactive layer/Al). We investigated the properties of the PSC devices featuring periodic nanostructures in the photoactive layers using reflection UV-vis spectra and in terms of their external quantum efficiency (EQE) and photocurrent-voltage characteristics. In addition, we used numerical simulations to evaluate the electromagnetic field distributions in the devices. The light trapping efficiency in the PSCs featuring periodic nanostructures was enhanced as a result of light scattering and surface plasmon resonance effects. Relative to conventional devices featuring a flat geometry, the power conversion efficiency of a thin (ca. 150 nm) photoactive P3HT/C₇₀ bilayer device increased by 90% when it featured a periodic nanostructure, with up to 20-fold increases in EQE observed at the absorption edge. Furthermore, when we engineered periodic nanostructures into bulk heterojunction devices incorporating a low-bandgap (LBG) photoactive layer (PTPTBT:PC₇₀BM), the photocurrent increased by 20%, suggesting that this facile light-harvesting system is suitable for both thin P3HT and LBG PSC applications in the visible to near-infrared (NIR) region.