Potential of very thin and high‐efficiency silicon heterojunction solar cells

Thin crystalline silicon (c‐Si) solar cells are highly attractive for realizing light‐weight and flexible wafer‐based solar cells as well as for reducing the material cost. Silicon heterojunction (SHJ) architecture using hydrogenated amorphous silicon (a‐Si:H) is suitable for realizing very thin c‐Si cells, because of its capability of excellent surface passivation. In this work, the potential of very thin c‐Si solar cells is examined by characterizing SHJ solar cells with a wide range of thicknesses from 50 to 400 μm. A trade‐off between the open‐circuit voltage (VOC) and the short circuit current density (JSC) against wafer thickness is clearly observed in these SHJ cells, whereas a decrease in fill factor (FF) is found for thin SHJ cells below 80 μm. The loss analysis for the thin SHJ cells with numerical simulation clarifies that the infrared parasitic absorption loss due to the supporting layers is enhanced for thinner wafers, which limits the JSC in the thin SHJ cells. In addition, it is confirmed that the FF is more sensitive to surface recombination than the VOC, and this tendency becomes more pronounced with the decrease in the wafer thickness. A high efficiency of 22% is achieved in a SHJ solar cell with a thickness of only 46 μm, demonstrating a high potential for flexible high‐efficiency c‐Si solar cells.