Organic Tandem and Multi-Junction Solar Cells


  • The authors gratefully acknowledge the co-workers at the University of Groningen and their collaborators at the Technical University of Eindhoven, the Energy research Centre of the Netherlands (ECN), and the University of Hasselt (Belgium). Financial supports from the Dutch Polymer Institute (DPI), Netherlands Agency for Energy and Environment (SenterNovem), Foundation for Fundamental Research on Matter (FOM), and the Zernike Institute for Advanced Materials are gratefully acknowledged.


The emerging field of stacked layers (double- and even multi-layers) in organic photovoltaic cells is reviewed. Owing to the limited absorption width of organic molecules and polymers, only a small fraction of the solar flux can be harvested by a single-layer bulk heterojunction photovoltaic cell. Furthermore, the low charge-carrier mobilities of most organic materials limit the thickness of the active layer. Consequently, only part of the intensity of the incident light at the absorption maximum is absorbed. A tandem or multi-junction solar cell, consisting of multiple layers each with their specific absorption maximum and width, can overcome these limitations and can cover a larger part of the solar flux. In addition, tandem or multi-junction solar cells offer the distinct advantage that photon energy is used more efficiently, because the voltage at which charges are collected in each sub-cell is closer to the energy of the photons absorbed in that cell. Recent developments in both small-molecule and polymeric photovoltaic cells are discussed, and examples of photovoltaic architectures, geometries, and materials combinations that result in tandem and multi-junction solar cells are presented.