Resonance Energy Transfer Enables Efficient Planar Heterojunction Organic Solar Cells

Poor energy transport in disordered organic materials is one of the key problems that must be overcome to produce efficient organic solar cells. Usually, this is accomplished by blending the donor and acceptor molecules into a bulk heterojunction. In this article, we investigate an alternative approach to cell design: planar mulitilayer hetrojunctions with efficient energy transport to a central reaction center. We use an experimentally verified Monte Carlo model of energy transport to show that an appropriately engineered planar multilayer stack can achieve power conversion efficiencies comparable to those of the best bulk heterojunction devices. The key to this surprising performance is careful control of the optical properties and thicknesses of each layer to promote Forster resonance energy transfer from antenna/transport layers to a central reaction center. We provide detailed design rules for fabricating efficient planar heterojunction organic cells.