Isolated alternative crystalline silicon phase could lead to improved solar cell performance

With its high absorption and efficient light emission capabilities, type II silicon clathrate can improve the performance of electronic devices. However, these technologies require high-quality silicon-clathrate films that are difficult to obtain. Liu et al. reported methods to isolate and characterize the intrinsic silicon-clathrate phase from a two-step synthesis process.

The authors found their technique isolated type II silicon clathrate, with sodium content low enough that the material is a “heavily doped” semiconductor. The material absorbs light about 100 times more efficiently than the diamond-crystalline form of silicon widely used in solar cells.

“Our work reveals that interpretation of measurements, like optical absorption, photoluminescence, and transport studies of such films to obtain fundamental properties of the clathrate phase, is affected by the presence of disordered alternative phases and, hence, can give misleading results. We also show how to remove these phases,” author Yinan Liu said. “The central importance of our work is that for the first time, new critical insights unravel the synthesis issues that have previously limited the fundamental understanding of silicon clathrates and provide a road map for further improvements, which can ultimately lead to revolutionary electronic applications for this novel silicon caged material.”

To synthesize the silicon-clathrate films, the team annealed sodium with a silicon wafer to form precursor sodium silicide film, decomposed the precursor into clathrate phase, then removed disordered silicon using film exfoliation and wet and dry etching. To characterize the films’ structure, composition, and optical properties, the authors used several techniques, including X-ray diffraction and photoluminescence.

The team plans to improve their method to produce thinner, purer, and more efficient silicon-clathrate films.

Source: “Synthesis and characterization of type II silicon clathrate films with low Na concentration,” by Yinan Liu, William K. Schenken, Lakshmi Krishna, Ahmad A. A. Majid, Thomas E. Furtak, Michael Walker, Carolyn A. Koh, P. Craig Taylor, and Reuben T. Collins, Applied Physics Reviews (2021). The article can be accessed at https://doi.org/10.1063/5.0062723 .