Efficiency Improvement of Organic Solar Cells Using 350 nm Surface Relief Grating by Holographic Lithography

There was inefficient light absorption in the thin active layers due to optical losses in Organic Solar Cells (OSCs) with relatively large area. Therefore, it is a key issue to have a light trapping structure for highly efficient OSCs. For high performance devices fabrication, a smart grating was fabricated using holographic photolithography incorporated with wet etching technology. Scanning electron microscopy (SEM) images of fabrication were employed before/after spin-coating active layer. With the aid of optical finite difference time Domain (FDTD) simulation for optical effect, the optimized device structure ITO (1D grating)/PEDOT:PSS (40 nm)/PBDB-T:ITIC (100 nm)/PDINO (5 nm)/Al (100 nm) was obtained. The experimental results showed that when the grating period was 350 nm, depth 40 nm, the power conversion efficiencies (PCE) reached to 9.51%, an apparent increase from those of the typical P3HT:PC71BM structure. This work indicates that the diffraction gratings had a potential to realize more efficient organic photovoltaics, if suitable fabrication processing methods can be developed.