Review—Development History of High Efficiency Silicon Heterojunction Solar Cell: From Discovery to Practical Use

Silicon heterojunction (SHJ) solar cells are attracting attention as high-efficiency Si solar cells. The features of SHJ solar cells are: (1) high efficiency, (2) good temperature characteristics, that is, a small output decrease even in the temperature environment actually used, (3) easy application to double-sided power generation (bifacial module) using symmetric structure. We have developed and actively evolved this SHJ solar cells from early 1990s, and introduced the module equipped with SHJ solar cells named as well-known “HIT ® ” in 1997. Since then, we have produced more than 500 MW of HIT ® per year for over 20 years. Although several companies have entered the market along the way, we are the only company with this scale of production. In this paper, we will discuss the history of the development, the unique feature of this solar cell, the technology development required to fabricate the module using these solar cells, and the efforts made to ensure reliability. By sharing our knowledge and reliability technology we have developed, we hope to accelerate the spread of SHJ solar cells, which are expected to become the next mainstream solar cells.