Tandem solar cell—concept and practice in organic solar cells

� Springer-Verlag Berlin Heidelberg 2015. In the past decade, organic solar cell (OPV) technology has been intensively studied and improved significantly due to its attractive properties in manufacturability, flexibility, light weight etc. The power conversion efficiency (PCE) has been enhanced dramatically from ~2–3 to ~12 % through materials, interface and device architecture innovations such as tandem. This chapter focuses on multi-junction or tandem solar cell which is the architecture for highest solar cell efficiency. First, the principle of solar photovoltaic process and the theoretical limits of solar cell in single and multiple junction cells were presented. After the brief description of the realization of tandem cell concept in inorganic solar cells, we provided an overview of the development of organic tandem solar cells. This includes two very distinct technologies—vacuum deposited small molecule tandem solar cells, and solution processed polymer tandem solar cells. The progress in active materials with different bandgap, interconnection layer, and tandem device structure are presented.