A research team in the Hong Kong Polytechnic University (PolyU) Department of Electronic and Information Engineering led by Professor Charles Chee Surya, Clarea Au Endowed Professor in Energy, has announced they have recently been successful in developing perovskite-silicon tandem solar cells which they claim have the world's highest power conversion efficiency of 25.5%.
According to the announcement there are different wavelengths for solar energy, a combination of different materials for making solar cells would work best for energy absorption. For example, methylammonium lead tri-halide perovskite and silicon solar cells can form a complementary pair.
With the perovskite solar cell functioning as a top layer, it can harvest the short wavelength photons while the bottom layer coated with silicon is designed to absorb the long wavelength photons.
Figure: Hong Kong Polytechnic - Perovskite tandem solar cell - 25.5% efficiency
PolyU's research team maximises efficiency by making use of this feature with three innovative approaches.
- low-temperature annealing process in dry oxygen to reduce the impact made by perovskite defects
- a tri-layer of molybdenum trioxide / gold / molybdenum trioxide with optimised thickness of each layer, making it highly transparent for light to go into the bottom silicon layer under perovskite layer
- mimicking the surface morphology of the rose petals, a haze film, developed by Dr Zijian Zheng of PolyU Institute of Textiles and Clothing, has been applied as the top layer of the solar panel to trap more light
All three innovative approaches help enhance energy conversion efficiency. Professor Shen Hui of Sun Yat-sen University and Shun De SYSU Institute for Solar Energy, who excelled in the fabrication high-efficiency silicon cells, was responsible for the design and fabrication of the bottom silicon cell.
PolyU research team will continue to improve the power conversion efficiency as well as the performance of large-scale fabrication of perovskite-silicon solar cells.
The researchers estimate that solar energy generated from these solar cells could achieve a cost of HK$2.73/W, compared with HK$3.9/W at present generated by existing silicon solar cells available in the market.