A team from the US Naval Research Laboratory (NRL), backed by Imperial College London and Microlink Devices, has taken an important step toward producing more efficient solar cells.
The team has created a model of a triple junction solar cell that may be able to break through the 50 per cent conversion efficiency barrier. The current record stands at around 44 per cent efficiency, and for solar cell scientists, the ability to convert half of the sun’s energy to electricity using photovoltaics would be a landmark achievement.
The materials used in the cell are all lattice matched, meaning that the lattice structures of the different materials are matched up so scientists can alter the bandgap, or electrical conductivity, without changing the structure.
Compared to other technologies, NRL research physicist Dr. Roberts Walters believes the triple junction cell will be competitive. He says other options such as inverted metamorphic (IMM) technology allow scientists to gain suitable bandgaps but offer reduced material properties.
The triple junction cell, meanwhile, offers optimum bandgaps alongside high material quality. Work with dilute nitride materials has achieved record high efficiency but the challenge with this technology is that there is only a limited range of achievable bandgaps in the 1eV and lower range, which is necessary for solar cells.
“Our material system offers a much wider range of readily achievable bandgaps in this range,” Walters confirms.
The results are currently based only on modelling, so there is still some development to be done on the project before the material is able to be used in photovoltaic applications. However, the scientists are now looking at creating the materials to realise their predictions.
“It took us about two years to develop our models, produce our target bandgap values, and identify our candidate material system,” Walters says. “The research is currently in its initial stages where we are focusing on the material development required to produce the InAlAsSb material. This will, as far as we know, be the first time this material has been applied to solar cells, and there are some significant material growth challenges to overcome. However, the material will eventually be commercialised. We are teamed with Microlink Devices Inc. who are a semiconductor manufacturing house currently producing IMM solar cells.”
If the team is able to create the solar cell, it will lead to a significant increase in power production capability from concentrated photovoltaic systems at a reduced cost. It will also allow engineers to produce solar cell technologies for renewable energy-based portable power sources as well as for highly efficient renewable energy power plants.