The photon absorber and interconnecting layers in multijunction organic solar cell

Organic photovoltaic devices have long been considered as an important alternative for coal-based energy technologies due to their low-cost, lightweight and flexible nature. However, the power conversion efficiencies of such cells are limited by thermalization and transmission losses, which can be overcome by stacking multiple cells in a tandem configuration. This approach allows utilization of the wider spectrum of solar light, helping in attaining the theoretical limits for single cell efficiency (~30%). However, the performance of such tandem organic solar cells depends largely on several factors, including the proper design of absorber, sub-cells and interconnecting layer materials. In this review, recent studies on the development of different fullerene, non-fullerene, small molecule acceptor based active layers have been reported. Also, some recent works in the field of the inorganic-organic hybrid tandem cells have been briefly discussed. The purpose of this review is manifold: to provide the readers with a comprehensive overview of past, current research, recent developments, and open problems of tandem organic solar cells.