Interface engineering for ternary blend polymer solar cells based on spectroscopic and device analyses

Polymer solar cells, which include a blend of electron-donating conjugated polymers and electron-accepting molecules in the photovoltaic layer, have been widely studied as next-generation solar cells. To improve photocurrent generation, it is necessary to harvest as many photons as possible in solar light, which distributes over a wide wavelength including the ultraviolet, visible, and near-infrared (near-IR) regions. However, covering such a wide solar spectrum by using binary blend polymer solar cells is inherently difficult because most organic materials (e.g., conjugated polymers) have a narrow absorption bandwidth (less than 200 nm). Ternary blend polymer solar cells can overcome this limitation by combining near-IR light-harvesting materials with the electron-donor conjugated polymer and the electron-acceptor molecule. In this review, recent progress in the development of polymer solar cells is briefly overviewed, followed by a detailed description of ternary blend polymer solar cells. Ternary blend polymer solar cells incorporating near-IR materials are among the most promising approaches for effectively improving photovoltaic performance because they can extend the light-harvesting wavelength range and simultaneously improve charge transport. Here, we briefly review the progress in polymer solar cells and describe our recent studies on ternary blend polymer solar cells incorporating near-IR dye molecules. Of particular importance is the interfacial engineering for the placement of near-IR dye molecules at the donor/acceptor interface in ternary blend polymer solar cells.