Researchers from ITMO University (Information Technologies, Mechanics and Optics) in St. Petersburg, Russia are testing compound A3B5 semiconductors in the manufacture of multi-junction III-V solar cells.

Multi-junction solar cells based on III-V compounds are commonly used in terrestrial photovoltaic modules and space solar arrays because they are the most efficient converters of solar energy to electricity.

A3B5 materials are semiconductors that include gallium arsenide (GaAs), indium arsenide (InAs), gallium phosphide (GaP), indium phosphide (InP), gallium antimonide (GaSb) and indium antimonide (InSb). These conductors are widely used in electronics and optoelectronic applications.

While these solar cells are great they can be quite expensive to make. This is why the team from ITMO University has been working toward a way to reduce the cost and at the same time increasing the efficiency of the cells.

For their latest experiments, they fabricated the top layer of a small prototype solar cell that featured A3B5 materials. This was integrated onto a silicon substrate, which was much less expensive than the materials used in III-V solar cells.

The epitaxial-synthesis-on-silicon-substrate is a difficult manufacturing process as 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.

GaP is a semiconductor that meets these requirements, but its light-trapping properties do not offer the best results. However, the gallium phosphide compound combined with nitrogen offers strong light-trapping properties and can be integrated onto the silicon substrate. The ITMO team commented:

At the same time, silicon doesn’t just serve as the building material for the photovoltaic layers – it can act as one of the photo-active layers of a solar cell, absorbing light in the infrared range.

They were able to continuously increase the efficiency of the solar cells when adding extra photoactive layers, and say that the A3B5 semiconductor can also be used in intermediate layers. The researchers believe that when combined with concentrating PV technology, these solar cells have the potential to reach 40% efficiency.

Next up for the team will be a way to produce these cells while reducing the cost.