Photovoltaic Absorber "Glues" for Efficient Bifacial Selenium Photovoltaics

Bifacial solar cells hold great potential for achieving higher power output than conventional monofacial devices by harvesting solar irradiance from both their front and rear surfaces. However, almost all currently reported bifacial devices typically require a sputtered rear transparent conducting oxide electrode, which can damage the underlying layers due to plasma effects during the deposition process. Here, we report a glue-bonding strategy that uses a high-viscosity photovoltaic absorber slurry-in the case of molten selenium (Se)-as the adhesive to bond two charge-transport layer-deposited commercial fluorine-doped tin oxide glasses, directly creating bifacial solar cells without the use of magnetron sputtering. We find that molten Se exhibits relatively high viscosity, high stability, and Newtonian fluid characteristics, facilitating film formation using this strategy. The resulting bifacial Se solar cells exhibit a bifaciality factor of 90.1%, surpassing all types of conventional thin-film solar cells. These cells achieve efficiencies of 8.61% under 1-sun illumination with an albedo of 0.3 and 26.17% under 1000-lux indoor illumination with an albedo of 0.8, with no efficiency loss after 1000 h of ambient storage.