Researchers at Russia’s ITMO University, in St Petersburg, are testing compound A3B5 semiconductors in the manufacture of multi-junction, III-V solar cells.
A3B5 materials are a family of semiconductors including gallium arsenide (GaAs), indium arsenide (InAs), gallium phosphide (GaP), indium phosphide (InP), gallium antimonide (GaSb) and indium antimonide (InSb) which are used as basic materials for electronic and optoelectronic applications.
The ITMO University team say they fabricated the top layer of a small, laboratory prototype solar cell which featured A3B5 materials integrated on a silicon-substrate for the first time. They claim the innovation could lead to highly efficient solar cells at considerably lower costs, as the silicon substrate used in their device was much less expensive than materials used in IIV-V solar cells – so named after the groups of the periodic table the elements concerned occupy.
The researchers said 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,” they said.
GaP is one semiconductor meeting those requirements but the researchers said its light trapping properties are limited. The gallium phosphide compound, however, when combined with nitrogen, shows direct-band property and strong light-trapping properties as well as being suitable for integration on the 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 photo-active layers of a solar cell, absorbing light in the infrared range,” the ITMO University team said.
The scientists said the efficiency of their solar cell rises as extra photo-active layers are added, and they claim the A3B5 semiconductor can also be used for intermediate layers. They believe the potential efficiency of such solar cells could top 40% if used with concentrating PV technology.
The findings were presented in the paper GaNP-based photovoltaic device integrated on Si substrate, published in Solar Energy Materials and Solar Cells, and on the ScienceDirect website.
Gallium arsenide and other III-V materials are among the best known in terms of efficiency potential for solar cells but cost has thus far limited them to niche applications such as powering satellites and drones.