Development of Wrinkled Surface for Enhanced Light Trapping in Organic Solar Cells

Abstract

There have been great interest in organic photovoltaics (OPVs) due to their potential for the development of low-cost, high throughput, and large-area solar cells with a flexible form factor. Hence, the power conversion efficiency of OPVs has been dramatically improved for the past two decades. Although the power conversion efficiency (PCE) of OPVs exceeds 10% now, the PCE of thin-film based solar cells is fundamentally limited by the ability of the photo-active layer to absorb the incident sunlight. The external quantum efficiency (EQE) is used to describe this ability and rarely exceeds 70% for the state-of-the-art OPVs, implying that only 70% of incident photons contributes to a photo-current generation. The EQE can be improved by trapping more light in the active layer which is very challenging for thin-film based photovoltaics. In this research, I have investigated optimization of the organic solar cell fabrication by tuning a charge carrier transport layer and also developed a new metallization method in order to replace vacuum deposited silver electrode with electroplated copper which is less expensive and better fits to the industry manufacturing. I also investigated a number of methods to fabricate optimum wrinkle structure that can be used as a light trapping vehicle for organic solar cells. I fabricated wrinkles on SU-8 polymer by controlling the softness of SU-8. While wrinkles generally produced after metal deposition, I found that a more suitable wrinkle profile can be fabricated before the metal deposition. Future work will focus on the development of reproducible, scalable, and high throughput wrinkle fabrication with an optimum profile and the demonstration of highly efficient organic solar cells by enhancing light trapping thanks to the wrinkles.