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AIST:Research Highlights, Development of a New Crystalline Silicon Solar Cell

Energy and Environment

Development of a New Crystalline Silicon Solar Cell

MATSUI Takuya, SAI Hitoshi
Global Zero Emission Research Center

Released: October 22, 2020

High efficiency, low cost solar cells using titanium oxide

The ability of titanium oxide to selectively extract holes from silicon was discovered, and a silicon solar cell with a titanium oxide thin film placed on the positive electrode side was fabricated and achieved conversion efficiency in excess of 20%.

Figure: Conceptual diagram of fabricated solar cell structure

Conceptual diagram of fabricated solar cell structure (example) (left), transmission electron microscopy image of interface between silicon and titanium oxide (upper right), and appearance of a sample with five solar cells formed on a 50 mm square crystalline silicon substrate (lower right)

Both improved conversion efficiency and reduced manufacturing costs

Crystalline silicon solar panels presently account for over 90% of the market. Pursuit of energy conversion efficiency increases manufacturing costs. In order to promote the introduction of solar power generation, it is necessary to simultaneously increase conversion efficiency and reduce manufacturing costs.

Use of titanium oxide in the positive electrode to improve conversion efficiency

It was demonstrated that a titanium oxide thin film with a thickness of approximately 5 nm exhibits both hole selectivity and the ability to inactivate surface defects of silicon (passivation), and can function as a positive electrode. The mechanism of these properties was investigated, and the results clarified that the passivation and hole selectivity can be controlled by the composition and distribution of the intermixed layer consisting of titanium, silicon, oxygen, and hydrogen present at the interface between the titanium oxide and the crystalline silicon. In addition, a prototype crystalline silicon solar cell with a titanium oxide thin film placed on the positive electrode side was fabricated and achieved conversion efficiency in excess of 20%.

A new ability of titanium oxide expands the range of application

Titanium oxide is a material known to inherently exhibit electron selectivity for silicon, and this research confirmed that hole selectivity can also be realized. Going forward, we intend to develop solar cells with a simple structure that applies titanium oxide to both positive and negative electrodes of silicon. Application of the newly developed technology can be expected to tandem solar cells that stack heterogeneous solar cells and silicon solar cells, and to photoelectrochemical devices and semiconductor devices, etc.