Semitransparent Single-Junction and Tandem Solar Cells Using Microcrystalline Silicon for Energy-Harvesting Photovoltaic Windows

Semitransparent solar cells, which can be incorporated in windows, façades, and skylights, change a part of incident light to electric power while allowing the rest to pass through. Improving the conversion efficiency and visible-light transmittance of such devices is a crucial factor for power-generating window applications. Herein, we report the fabrication of semitransparent single-junction and tandem devices using microcrystalline silicon (μc-Si) with front and rear transparent conducting oxide electrodes by plasma-enhanced chemical vapor deposition. The material properties of the p-doped silicon-carbide (SiC) films and the interfaces between p-layer and intrinsic μc-Si were optimized to enhance the solar cell performance. By using highly crystalline seed layers for the intrinsic μc-Si absorbers and controlling the properties of high-bandgap p-SiC films, high power conversion efficiency (PCE) and average visible transmittance (AVT) of 4.71 and 12.31%, respectively, were simultaneously obtained for the semitransparent devices using 1000-nm-thick μc-Si absorbers. Their performance at different low light intensities was also investigated. The devices showed steady PCEs of 4.37–4.71% at low light intensities (100–21 mW/cm2). Enhanced PCE of 7.51% and AVT of 11.00% are achieved in high-quality semitransparent tandem devices with amorphous silicon and μc-Si subcells. The corresponding tandem solar cells showed further increased PCE of 9.00% under bifacial illumination condition.