Benzophosphole Oxide and Sulfide for Thermally Stable Cathode Buffer Layers in Organic Thin-Film Photovoltaic Devices

摘要

Organic thin-film photovoltaics (OPV) has drawn increasing attention as a next-generation photoelectron conversion device owing to its potentially low cost and less energy-demanding manufacturing process. The primary issues from among the many problems that still need to be solved are the efficiency and stability of the device, which depend on the nature of the materials as well as the device structure. Although the stability of the active layer, where charge separation takes place, has been widely discussed, the stability of the cathode buffer layer and suitable n-type materials have received less attention. We addressed the issue of suitable materials for a recently reported solution-processed OPV device composed of a crystalline active layer containing benzoporphyrin (BP) and bis(triorganosilymethyl) [60]fullerene (SIMEF) (Figure 1). This device possesses a well-defined and thermally stable bulk heterojunction, and hence provides a platform suitable for examining the properties of cathode buffer materials to be coated above it. Although bathocuproine (BCP) is widely used, it has quite a low glass transition temperature (T_(g)velence62 deg C), and hence there is concern about the thermal instability of the device. The literature suggests only a few cathode buffer materials that offer high morphological stability.