Silicon solar cells have captured 91% of the PV market due to their economic competitiveness. However, the efficiency of the best silicon solar cells has stayed at around 25% for the last 15 years. Cells made of materials in the 3rd and 5th column of the periodic table (III/V materials) have reached efficiencies close to 45% but are prohibitively expensive. Prof Barnett’s research group has combined the best of both worlds: the affordability of silicon with the high efficiency of III/V materials.
The first fabrication steps for these structures are undertaken by industry partners in the United States, with a SiGe buffer layer grown on a Si substrate at AmberWave Inc via reduced pressure chemical vapour deposition (RPCVD). A GaAsP top solar cell layer is then grown at Veeco via metal organic chemical vapor deposition (MOCVD). The SiGe buffer layer is designed to complete the lattice constant transition from Si to GaAsP in order to maintain high material quality, which is indispensable for high performance. SiGe can also be designed as a high quality bottom solar cell to form a dual junction solar cell to increase power output.
At UNSW, this material stack is turned into working solar cells using lithography, metal deposition and wet etch capabilities at ANFF-NSW to complement fabrication processes available within the School of Photovoltaic and Renewable Energy Engineering. To date, the team has achieved efficiencies up to 20.6% with this GaAsP/SiGe solar cell design. However, this design has the potential to overtake Si and achieve efficiencies up to 40%.