The development of GaAs solar cells began in the 1950s and has a history of over 50 years. In 1954, the photovoltaic effect of GaAs materials was first discovered. In 1956, J.J. Loferski and his team explored the optimal material properties for manufacturing solar cells, indicating that materials with an Eg value in the range of 1.2–1.6 eV had the highest conversion efficiency. Currently, the highest efficiency of GaAs cells in the laboratory has reached 50%.
GaAs solar cells are a type of group III-V compound semiconductor solar cell. Compared with Si solar cells, their characteristics are as follows:
(1) High conversion efficiency.
GaAs has a wider bandgap than Si, and its spectral response characteristics match the solar spectrum better. Therefore, GaAs solar cells have a higher photoelectric conversion efficiency than Si solar cells. The theoretical efficiency of Si cells is only 23%, while the theoretical efficiency of a single GaAs cell is 27%, and the theoretical efficiency of a multi-cell GaAs cell is as high as 50%.
(2) It can be made into an ultra-thin battery.
GaAs is a direct bandgap semiconductor, while Si is an indirect bandgap semiconductor. In the visible to infrared spectrum, GaAs has a much higher absorption efficiency than Si. To absorb 95% of sunlight, Si requires a thickness of more than 150 μm, but GaAs only needs 5 μm to 10 μm. Solar cells made of GaAs can be significantly lighter.
(3) High temperature resistance
GaAs has a low intrinsic carrier concentration, resulting in a significantly lower maximum power temperature coefficient (-2 × 10⁻³ °C⁻¹) compared to Si (-4.4 × 10⁻³ °C⁻¹). At 200 °C, Si solar cells cease to function, while GaAs solar cells still maintain an efficiency of approximately 10%. This makes GaAs cells well-suited for applications in concentrated solar power.
(4) Good radiation resistance
GaAs has a short minority carrier lifetime, and damage occurring a few degrees of diffusion away from the junction has no effect on photocurrent or dark current. Therefore, its resistance to high-energy particle irradiation is superior to that of Si solar cells with indirect bandgap. Under irradiation conditions of 1 MeV electron energy and 1 × 10¹⁵ electrons/cm², the power output ratio of solar cells after irradiation to before irradiation is >0.76 for GaAs single-junction solar cells, >0.81 for GaAs multi-junction solar cells, while only 0.70 for BSFSi solar cells.
(5) It can be made into a more efficient multi-junction tandem solar cell.
With the continuous improvement of MOCVD technology, significant breakthroughs have been achieved in the growth technology of group III-V ternary and quaternary compound semiconductor materials (GaInP, AlGaInP, GaInAs), providing a variety of materials to choose from for the development of multi-junction tandem solar cells.
Comparison of gallium arsenide solar cells and silicon photovoltaic cells
1. Photoelectric conversion efficiency:
Gallium arsenide (GaAs) has a wider bandgap than silicon, resulting in better spectral response and space solar spectrum matching capabilities. The theoretical efficiency of silicon solar cells is approximately 23%, while single-junction GaAs cells achieve a theoretical efficiency of 27%, and multi-junction GaAs cells exceed 50%.
2. Temperature resistance
Generally speaking, gallium arsenide (GaAs) solar cells have better temperature resistance than silicon solar cells. Experimental data shows that GaAs solar cells can still work normally at 250°C, while silicon solar cells cannot work normally at 200°C.
3. Mechanical strength and specific gravity
Gallium arsenide is more brittle than silicon in terms of physical properties, which makes it easier to break during processing. Therefore, it is often made into thin films and a substrate (usually Ge [germanium]) is used to counteract this disadvantage, but this also increases the complexity of the technology.
