Improved adhesion of multi-layered front electrodes of transparent a-Si:H solar cells for varying front colors

Abstract

A low temperature deposition process was developed to fabricate ultra-thin, transparent, multi-layered electrodes (TMEs) suitable to be used on variously shaped flexible substrates, as those utilized in the transparent solar cells of building-integrated photovoltaic (BIPV) systems. The fabricated TMEs consisted of a bottom layer (BL) of gallium doped zinc oxide (GZO), an Ag-layer, and optoelectronic-controlling layers (OCLs) of GZO; and exhibited a high transmittance of 90% at 550 nm, and a low sheet resistance of 9.4 Ω/sq. at the thickness of ~ 100 nm. Because the Ag of TMEs easily detach from inorganic or amorphous surfaces, the GZO-BL was chemically treated in a diluted acetic and nitric acid mixture (10:2) to generate changes in its surface energy and improve the Ag adhesion. To quantitatively evaluate the Ag adhesion of TMEs, we proposed and conducted a tape pull-out adhesion test, and found the optimum GZO-BL texturing condition. The developed TMEs were used as the front transparent conductive electrodes of transparent a-Si:H solar cells to tune their reflection colors. By changing the thickness of the OCL, a wide range of colors was obtained without serious efficiency variations, as was predicted by optical simulations. The fabricated transparent cells show a high efficiency of 4.8%, as well as a high average transmittance of ~ 20% in the visible range. The developed TME structure, using the proposed deposition process, can be fabricated on various substrates and can be applied to devices that require a variety of colors such as BIPVs, wearable PVs, and the PVs of moving vehicles.