This report discusses the project results and lessons learnt to date for the UNSW Project, Next Generation Silicon Sub-cells for High Efficiency III-V/Si Multi-junction Solar Cells.
During the first 18months of this project the target was to determine the viability of a novel design of III-V semiconductor materials on silicon multi-junction solar cell. The III-V on silicon multi-junction approach offers the prospect of high efficiency with lowered costs due to the use of industrially ubiquitous silicon. Working closely with our collaborators at Ohio State University in the United States, we have worked on developing alternative structures to achieve these ends.During this period our collaboration has achieved the world record efficiency for a two junction multi-junction III-V on silicon device, providing proof of the leading role this team is playing.
Work has covered the use of more conventional structures for the silicon bottom cell, with UNSWs deep knowledge in silicon processing being used to explore different rear structures to achieve highest performance.Utilisation of a room temperature metal contacting technique developed in another ARENA funded project has begun, an approach expected to provide benefits due to the lack of high temperature processing required. Detailed simulations have also been performed, using an advanced device simulator tool, TCAD, to explore the use of alternate materials for the rear surface of the silicon cell. Materials that will preferentially block electron flow at the rear have been identified and are currently being explored for use in advanced designs.
Reduction of silicon used in these devices is being explored by the use of silicon thinner than previous efforts. The challenges of using this approach remain substantial, but encouraging results suggest this is a worth while approach. All of the technical milestones for this reporting period have been met, with further deep improvements to come. The ultimate goal of looking at completely new designs for III-V on silicon solar cells remains viable for this project.