Tandem PV Micro Concentrator Project Results and Lessons Learnt

The project aims to produce a commercially competitive micro concentrator tandem solar module with over 30% efficiency.

The best commercial and laboratory silicon-only solar cells have efficiencies in the range 23-26%. In order to reach efficiencies of 30% and beyond, tandem solar cells comprising of two or more different materials must be used. Silicon (Si) is often used as the rear cell in tandem devices along with a higher bandgap top cell.

III-IV materials such as gallium arsenide (GaAs) are promising candidates as high bandgap top cell due to the excellent efficiency and stability of the material. However, these materials are expensive. In order to develop a commercially competitive GaAs/Si tandem solar cell system, the cost of the GaAs component must be reduced. This project aims to achieve this by using the ANU developed Sliver technique for creating GaAs solar cells, in conjunction with a micro concentrator system.

Individual measurements of the GaAs solar cells under concentrated light, combined with simulated performance measurements of the underlying silicon cell, indicate a tandem efficiency ≥ 30% can be achieved using this system.

Initial measurements of a complete, integrated concentrator/GaAs/Si device have been completed, demonstrating that the components can all function together effectively. Further improvements in the devices in areas such as anti reflection coatings and bonding materials are ongoing.

The creation of narrow grooves into the GaAs wafer (an integral part of the Sliver process) has been achieved using dicing. Other methods have been tested and ICP/RIE etching identified as a likely candidate for further improving the pitch and quality of the groove etching. The production of narrow GaAs grooves and the demonstration of a fully functioning tandem micro concentrator device are important steps towards achieving the final goal of a producing an efficient, commercially viable tandem PV micro concentrator.