9 - New Directions for Organic Thin-Film Solar Cells: Stability and Performance

Abstract

Organic solar cells have been steadily developed for more than two decades, not only attaining rapid improvements of their power conversion efficiencies but also progress toward commercialization. The power conversion efficiencies of single-junction organic solar cells have recently exceeded 14%, by energy gap engineering, improvement of charge carrier mobilities and optimization of the bulk-heterojunction morphologies. Intrinsic energy losses for separating the strongly bound excitons in organic semiconductors, however, set limitations for the maximum achievable power conversion efficiency. Multijunction solar cells, photon upconversion and downconversion, and exciton singlet-fission concepts provide new directions to overcome the single-junction limit. The successful commercialization of organic solar cells furthermore requires new directions for reliable upscaling processes toward large-area fabrication and for thermal, mechanical, and long-term stability.