The utility of III-V solar cells — a name denoting where the materials used to make them are positioned on the periodic table of elements — for terrestrial applications improves with a new fabrication process developed at the U.S. National Renewable Energy Laboratory.

Solar cells based on gallium arsenide (GaAs) and gallium indium phosphide (GaInP) deliver some of theSchematic of the simulated and experimentally realized rear heterojunction devices. Source: Cell Reports Physical Science doi.org/10.1016/j.xcrp.2023.101541 highest conversion efficiencies of any photovoltaic technology. However, lowering production costs to make them viable for mainstream solar applications remains a challenge. To address this, the researchers applied a combination of device modeling and experiment to demonstrate the economic and efficiency benefits of using heterojunctions in III-V solar cells.

Dynamic hydride vapor phase epitaxy was tested as an alternative lower-cost solution to metal organic vapor phase epitaxy for solar cell synthesis. This process uses low-cost elemental group III precursors with high utilization efficiency and very high growth rates. An emitter layer of gallium indium arsenide phosphide (GaInAsP) was also applied to form the heterojunction together with the GaAs absorber. An optimum emitter doping density and energy bandgap were identified to maximize the cell efficiency.

The rear heterojunction solar cell that served as a baseline used an emitter comprised of GaInP and had a reported efficiency of 26%. By reducing the doping in the emitter and changing its composition from GaInP to the lower bandgap GaInAsP, the efficiency increased to 27% even though the rest of the device was exactly the same.

The research is published in the journal Cell Reports Physical Science.