Efficient light trapping structures for organic photovoltaics fabricated by nanoimprint lithography

To improve the efficiency of organic photovoltaics (OPVs), the trapping of incident light with surface nanostructures, such as moth eye structures, is a highly useful strategy for enhancing absorption in the photoactive layer. Nanoimprint lithography is a widely used technique to produce large-area nanostructures cost effectively. However, the moth eye texture fabricated by the nanoimprint process necessarily contains a spatial clearance between adjacent cones, which could degrade the antireflective property of the textured surface. In this study, we perform optical simulations for the OPVs with moth eye coating to explore the effects of the spatial clearance in the moth eye array as well as its geometric pattern on the photocurrent generation. We show that the photocurrent level decreases significantly and superlinearly with increases in the size of the spatial clearance in moth eye, suggesting the importance of sufficiently narrowing the clearance size. Furthermore, we experimentally measure the performance of the OPV cell incorporated with the moth eye structure having a near-optimal geometric pattern with reduced clearance size to verify the simulation results.