Holographic spectral beamsplitting for increased organic photovoltaic conversion efficiency

Thermodynamic principles limit the conversion efficiency of a single bandgap organic photovoltaic (OPV) cell to 33%1. In order to increase efficiency, multiple OPV devices can be combined to cover a larger spectral range of the incident solar spectrum. The most common way of doing this is to mount multiple bandgap cells in tandem or series. However, stacked multijunction systems have limitations, such as current-matching constraints and optical quality of the OPV layer. A separated arrangement with spectrum splitting is a promising alternative to the stacked tandem approach. In this paper, two organic photovoltaic cells with complementary EQE curves are integrated into a holographic spectrum splitting module. The highest possible conversion efficiency of this two-cell combination is quantified assuming an ideal spectral filter as a reference. A spectrum splitting module is built, consisting of a reflective hologram oriented at an angle to split the incident beam into two spectral bands. The holographic beamsplitting system is assembled and studied under a solar simulator. Power output and conversion efficiency of the holographic spectrum splitting system is evaluated in terms of Improvement over Best Bandgap (IoBB) of the two-cell combination. The combined system has a measured improvement over its best single cell of 12.30% under a solar simulator lamp and a predicted improvement of 16.39% under sunlight.