Transparent, near-Infrared Organic Photovoltaic Solar Cells for Window and Energy-Scavenging Applications

Building integrated photovoltaic technologies are an enticing route to capturing large areas of solar flux necessary to offset a significant portion of our non-renewable energy consumption.  In this work we explore a route to high-efficiency and high-transparency solar cells that can be integrated onto window panes in homes, skyscrapers, and automobiles to enhance the functionality of already utilized transparent surfaces.  We exploit spectrally-discrete excitonic features of molecular photoactive layers to position the solar cell absorption in the near-infrared (NIR), leaving the visible part of the spectrum largely unaffected.  By optimizing the near-infrared optical interference generated within the transparent ITO contacts, we demonstrate planar heterojunctions with power conversion efficiencies of 1.3±0.1% and simultaneous average transmission across the visible spectrum of > 65%.    This selective photoactivity in the NIR also allowed us to further optimize the architecture with the use of a transparent NIR reflector, resulting in an efficiency of 1.7±0.1%, approaching the 2.4±0.2% efficiency of the opaque control cell while maintaining high average visible transparency of > 55%.  Finally we demonstrate a useful application of this technology, whereby a series of the transparent cells are monolithically integrated to power small electronic components with low-light levels.  This transparent photovoltaic architecture suggests new strategies for high-efficiency power generating windows, and highlights an application benefiting from excitonic electronics.