The Potential of Tandem Photovoltaic Solar Cells for Indoor Applications

Several studies have already determined the power potential of different types of solar cells for indoor applications. However, a detailed study whether or not the use of tandem solar cell (i.e. using two solar cells with different bandgaps in a row) is beneficial for indoor use is lacking. This paper attempts to fill this lacuna by comparing the power output of different tandem solar cells with single-junctions as reference. The comparisons are done by efficiency simulations based on the quantum efficiencies of the solar cells and the light spectra of typical artificial light sources, i.e. different types of fluorescent tubes, a high pressure sodium and metal halide lamp, a cool and warm LED lamp and a common incandescent and halogen lamp, which are compared to the outdoor AM1.5 spectrum as reference. More specifically, we study the influence of the energy levels of the bandgaps, as well as different absorption windows of the subcells. We not only study the light harvesting potential of the usual monolithic configuration, but also consider a stacked set-up. By determining the relative efficiency gain compared to single-junctions, we prove the limited usefulness of tandem solar cells for indoor applications and determine the acceptable range of bandgaps and absorption windows of the subcells for the different indoor environments.