Photochemical Upconversion Applied to Organic and Thin Film Silicon Solar Cells

The efficiency of thin-film solar cells with large optical band gaps, such as organic bulk heterojunction or amorphous silicon solar cells, is limited by their inability to harvest the (infra)red part of the solar spectrum. Photochemical upconversion based on triplet-triplet annihilation (TTA-UC) can potentially boost those solar cells by absorbing sub-bandgap photons and coupling the upconverted light back into the solar cell in a spectral region that the cell can efficiently convert into electrical current. In this presentation we augment two organic solar cells and one amorphous silicon (a-Si:H) solar cell with a TTA-upconverter as shown in figure 1, demonstrating a solar cell spectral response peak enhancement of up to 13% and an overall photocurrent increase of up to 0.15% under a moderate concentration (17-30 suns) (see figures 2 a,b). The behaviour of the organic solar cells, whose augmentation with an upconverting device is so-far unreported, is discussed in comparison to a-Si:H solar cells. Thin film hydrogenated amorphous silicon (a-Si:H) solar cells of the pin type were the first type of cells where TTA-UC was proven to work under moderate concentration [1]. Here we report on a substantial improvement by adding a backreflector to the UV/solar cell stack [2] and by significantly improving the conversion efficiency of the a-Si:H pin solar cell to 6.9%).