Recent patent issues on intermediate reflectors for high efficiency thin-film silicon photovoltaic devices

The recent surge of unveiled US patents on the intermediate reflectors for thin-film silicon (Si) photovoltaic (PV) devices reflects the paramount importance of light trapping to improve the conversion efficiency. Here, the recent patent issues on the intermediate reflectors of thin-film Si PV devices are reviewed. Highly transparent and conductive metal oxide intermediate reflectors have the advantage of the higher efficiency for the fabricated multi-junction solar cells compared to the Si alloy intermediate reflectors. However, their high lateral electrical conductivity leads to the lateral shunting during the monolithic series integration of segments. To avoid the lateral shunt creations, an additional laser scribe or a coating process that induces a high production cost is necessary. In addition, a low conversion efficiency for hydrogenated amorphous silicon (a-Si:H)/hydrogenated microcrystalline Si (μc-Si:H) double-junction PV modules employing a metal oxide intermediate reflector stems from the decrease in the active area as a result of the additional process. Meanwhile, double-junction PV modules employing an n-type hydrogenated microcrystalline Si oxide (n-μc-SiOx:H) intermediate reflector provide a higher conversion efficiency. Since the Si alloy intermediate reflector can avoid the lateral shunting, it may be a promising option for cost-effective mass production of large-area thin-film Si multi-junction PV modules. Although the developed intermediate reflectors have the high potential, the current status is limited at the research and development (R&D) level. Therefore, the up-scaling with the low cost, high throughput, and high yield is a key technological mission for mass production.