Energy harvesting performance of bifacial and semitransparent amorphous silicon thin-film solar cells with front and rear transparent conducting oxide contacts

Abstract

Bifacial and semitransparent hydrogenated amorphous silicon (a-Si:H) thin-film solar cells were prepared with front and rear transparent conducting oxide (TCO) contacts using a plasma-enhanced chemical vapor deposition process. Increased power conversion efficiencies (PCEs) and average visible transmissions (AVTs) in the visible wavelength range were realized in the cases of the bifacial and semitransparent solar cells based on the optimization of the device designs, such as front TCO contacts, intrinsic a-Si:H absorbers (i-a-Si:H), p-type hydrogenated nanocrystalline silicon carbide, and n-type hydrogenated nanocrystalline silicon layers. The dependencies of the performance parameters of the solar cells on the illumination direction and intensity were also investigated systematically. As the film thickness of the i-a-Si:H absorber layers increased from 150 nm to 450 nm, the PCEs of the solar cells respectively increased in the ranges of 6.01–7.50% and 5.25–6.25% when front and rear illuminations were used for a standard light intensity of 100 mW/cm2, while the AVTs decreased from 22.76% to 15.67% irrespective of illumination direction. The best PCEs of the bifacial and semitransparent solar cells that were fabricated with the use of optimal conditions were respectively equal to 7.94% and 6.20% when front and rear illumination conditions were used. The corresponding AVT was equal to 14.34%. The performance parameters of bifacial and semitransparent a-Si:H solar cells at varying illumination intensities in the range of 10–100 mW/cm2 were also investigated, and yielded consistent PCE values in the range of 6.39–6.62% with front illumination, and 4.95–5.15% with rear illumination.