Effects of a Period and a Contact Angle on Absorption Performance of Hemispherical-Shell-Shaped Organic Photovoltaic Cells

Abstract

For wearable electronics applications, organic photovoltaic (OPV) cells are good candidates as sources of renewable energy. Many efforts have been devoted to increasing energy conversion efficiency in OPV cells, and improvement in light retention has been one of the main research directions. Within this context, our group recently proposed an OPV cell structure with a hemispherical-shell-shaped (HSS) active layer and discovered that it has high potential for substantial enhancement in absorption performance. As a continuation of the study, this paper reports an in-depth investigation of the proposed device, examining the effects of several design parameters on its absorption performance. Using finite element analysis, it is found that the absorption performance depends on the periodicity type, and that a hexagonal type results in higher absorption than a square one due to its closer shape resemblance to a circular cross-section. The absorption performance is also affected by a contact angle, i.e., the angle made between a sphere and a flat part of the structure. It is learned that the average integrated absorption generally increases along with the contact angle, which saturates at around 80 deg of contact angle. Lastly, the effects of a cell period are studied, and it turns out that the average integrated absorption decreases as the period increases. It is also observed that at high incidence angles (>similar to 75 deg ), an array with a shorter period results in lower absorption than one with a longer period owing to a partial obstruction issue. All of these results support the understanding that the primary contribution of absorption enhancement in the proposed HSS structure comes from improved light retention rather than from a simple advantage in active layer volume. It is envisaged that these study outcomes will provide important guidelines in the design of HSS OPV cells.