High-efficiency HIT solar cells with a very thin structure enabling a high Voc

To increase the competitiveness of HIT (Heterojunction with Intrinsic Thin-layer) solar cells, we have been working on the enhancing their conversion efficiency. This time, we improved the heterojunction of the HIT solar cell, which made it possible to enhance the cell conversion efficiency. In addition, we have developed module technologies such as a new tab design and anti-reflection coated glass. By combining these technologies, we have achieved 240-W model with module conversion efficiency of 19.0%. Those HIT solar cells have the world´s highest level of cell conversion efficiency 21.6% at the mass-production stage. We have also been investigating the performance of thinner HIT solar cell using crystalline silicon (c-Si) wafers less than 100 μm in thickness. To minimize optical losses, such as the ultraviolet light absorption in the front transparent conductive oxide (TCO) layer and amorphous Si (a-Si) layers, and the near-infrared light absorption in the rear TCO layer, we have improved the deposition conditions of a-Si, and developed the TCO material respectively. To improve the surface passivation quality of the a-Si/c-Si heterointerface, we have examined our fabrication process from these three viewpoints: (1) the cleanliness of the c-Si surface, (2) the damage in the deposition process, and (3) the quality of the deposited a-Si layer. As a result, we have achieved an excellent Voc of 0.747 V with 58- and 75-μm-thick cells.