Heterojunction Silicon Solar Cells

Heterojunctions can be found in a wide variety of solar cells. This chapter presents the basics of heterojunctions and draws on the basics of homojunctions. It reviews the development of the silicon heterojunction cell (SHJ). Proper analysis of band diagrams thus is necessary to understand device performance. The silicon heterojunction solar cell is based on a device structure that combines thin film and bulk silicon technology. Of particular interest is the heterojunction cell with an intrinsic thin layer (HIT) with which Sanyo had achieved a very high efficiency of 23% in 2009, and of 25.6% efficiency most recently. This strongly challenges the standard high efficiency c-Si homojunction cell. Surface passivation of the c-Si wafer is a key requirement to optimize the performance of SHJ solar cells. Generally, surface passivation is ascribed to two different phenomena, namely, chemical passivation and field effect passivation.