Flexible Organic Solar Cells: Progress and Challenges.

Compared with inorganic photovoltaic technologies, flexibility is the most prominent feature of organic solar cells (OSCs). Flexible OSCs have been considered as one of the most promising directions in the OSC field, and have drawn tremendous attention in recent years. However, the power conversion efficiencies (PCEs) of flexible OSCs still lag behind those of their rigid counterparts. To further improve the performance of flexible OSCs, it is of great necessity for synergistic efforts to optimize flexible transparent electrodes (FTEs), photoactive materials, electrode buffer layers, and device structure engineering. Herein, the recent progress in flexible OSCs from the perspective of FTEs, including indium tin oxides, carbon nanomaterials, conducting polymers, silver nanowires, and ultrathin metal films and metal meshes, is summarized. In addition, the photoactive materials and electrode buffer layers in flexible OSCs are discussed to reveal the effects of material engineering and interface modification. Finally, a discussion of the future outlook and challenges of flexible OSCs is presented.