New Approach to Reduce the Price of Multi-Junction Solar Cells

A research team from St. Petersburg has now suggested an empirically tested and novel technology that can be used for producing highly efficient solar cells that are based on A3B5 semiconductors incorporated on a silicon substrate.

It has been estimated that in the days to come, the silicon substrate may boost the efficiency of the current single-junction photovoltaic converters by as much as 1.5 times. The Nobel Laureate Zhores Alferov had predicted the advancement of the new technology. The study results were published in the Solar Energy Materials and Solar Cells journal.

These days, the rising concern about environmental problems and the rapid depletion of hydrocarbon fuel reserves have pushed researchers to focus more on the development of what is known as the “green technologies.” The advancement of solar energy technologies is one of the most famous topics in the field.

But several factors obstruct the more extensive application of the solar panels. Traditional silicon solar cells exhibit a much low efficiency, that is, below 20%. In addition, more efficient technologies need relatively more intricate semiconductor technologies that considerably increase the cost of the solar cells.

The researchers at St. Petersburg have now suggested a new solution to overcome this challenge. The team from ITMO University, the Ioffe Institute, and St. Petersburg Academic University demonstrated that A3B5 structures can possibly be grown on a low-cost silicon substrate, thereby driving down the cost of multi-junction solar cells.

Our work focuses on the development of efficient solar cells based on A3B5 materials integrated on silicon-substrate. The main difficulty in the epitaxial synthesis on silicon-substrate is that the deposited semiconductor must have the same crystal lattice parameter as silicon. Roughly speaking, the atoms of this material should be at the same distance from each other as are the silicon atoms.

Ivan Mukhin, Study Co-Author and Researcher, ITMO University

Mukhin continued, “Unfortunately, there are few semiconductors that meet this requirement - one example is gallium phosphide (GaP). However, it's not very suitable for the fabrication of the solar cells since it has poor sunlight-absorbing property. But if we take GaP and add nitrogen (N), we obtain a solution of GaPN.”

Even at low N concentrations, this material demonstrates the direct-band property and is great at absorbing light, as well as having the capability to be integrated onto a silicon substrate. At the same time, silicon doesn’t just serve as the building material for the photovoltaic layers—it itself can act as one of the photoactive layers of a solar cell, absorbing light in the infrared range. Zhores Alferov was one of the first to voice the idea of combining ASB5 structures and silicon,” Mukhin added.

Mukhin is also the head of a laboratory at St. Petersburg Academic University.

While working at the laboratory, the researchers successfully achieved the top layer of the solar cell, which was incorporated into a silicon substrate. As the number of the photoactive layers increased, so did the efficiency of the solar cell, as each photoactive layer absorbs its portion of the solar spectrum.

At present, the scientists have created the world’s first tiny model of a solar cell that is based on the A3B5 semiconductor on a silicon-substrate. The team is currently working to develop a solar cell that would contain many photoactive layers. Solar cells like these will be considerably more effective at harvesting sunlight and producing electricity.

We’ve learned to grow the topmost layer. This material system can potentially also be used for intermediate layers. If you add arsenic, you obtain quaternary GaPNAs alloy, and from it several junctions operating in different parts of the solar spectrum can be grown on a silicon substrate.

Ivan Mukhin, Study Co-Author and Researcher, ITMO University

As demonstrated in our previous work, the potential efficiency of such solar cells can exceed 40% under light concentration, which is 1.5 times higher than that of modern Si technologies,” Ivan Mukhin concluded.


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