Application of Indium Tin Oxide/Aluminum-Doped Zinc Oxide Transparent Conductive Oxide Stack Films in Silicon Heterojunction Solar Cells

As an alternative to indium tin oxide (ITO), aluminum-doped zinc oxide (AZO) has been actively investigated due to its low cost. In this study, different transparent conductive oxide (TCO) structures, including AZO, ITO, ITO 50%/AZO 50%, ITO 25%/AZO 75%, and ITO 25%/AZO 50%/ITO 25%, were investigated comparatively on the back of the silicon heterojunction (SHJ) solar cell with a rear emitter. The crystalline structure, electrical and optical properties of all the films, and I–V performance of the corresponding SHJ solar cells were analyzed. It was found that the direct application of the individual AZO film onto the rear emitter of the SHJ solar cell could result in conversion efficiency reduction for the solar cell due to the poor contact of a-Si:H(p)/AZO and the low electrical and optical properties of AZO. However, by controlling the deposition conditions carefully, the stack structure of both ITO 50%/AZO 50% and ITO 25%/AZO 50%/ITO 25% could present good performance very close to that of individual ITO. The performance of the solar cells with the two kinds of TCO stacks as the back TCO had been greatly improved compared to the solar cell with the individual AZO. The efficiency gap for the solar cell with the individual ITO could be narrowed to within about 0.1% (absolute value). The results show the possibility of applying the ITO/AZO stack structure in the SHJ solar cell to reduce ITO consumption.