Efficiency boost for large perovskite panels and tandem cells
Researchers in Switzerland, Italy and China have found a way to scale up the production of large solar panels using low cost perovskite materials.
One of the obstacles on the way to commercializing perovskite solar cells is that scaling them up results to losses in power-conversion efficiency and operational stability. This is due to natural defects in the perovskite molecular structure, which interferes with the flow of electrons. This results in “resistive loss” – a power loss due to resistance. In addition, the processes required to achieve high-quality large-area perovskite films are quite complex.
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A team led by Mohammad Nazeeruddin at EPFL in Neuchatel have found a way to overcome the scaling up problems of perovskites. The scientists have developed an easy thermal method that can produce single-crystalline titanium dioxide rhombohedral nanoparticles that can be used to build a perovskite film.
The new structure reduces the density of lattice mismatches in the titanium dioxide nanoparticles. This translates into a lower number of defects, which ensures better electron flow throughout with lower power loss.
Small cells achieved a power-conversion efficiency of 24.05% and a fill factor of 84.7%. The cells also maintain about 90% of their initial performance after continuous operation for 1400 hours, which is a key challenge for large perovskite panels.
The scientists also built large cells with an active area of 24cm2 and an efficiency of 22.72%. This is the highest efficiency modules with the lowest loss in efficiency when scaling up.
The team worked with the Luxembourg Institute of Science and Technology (LIST) and CNR-SCITEC in Italy as well as the University of Perugia, Istituto Italiano di Tecnologia, Prince Mohammad Bin Fahd University in Saudi Arabia and University of Würzburg in Germany.
There were also eight Chinese partners in the project with the North China Electric Power University, Huazhong University of Science and Technology, Chinese Academy of Sciences (CAS), Xi’an Jiaotong University, Huaqiao University, City University of Hong Kong, Hebei University and Westlake University.
Record tandem perovskite cell
Researchers at EPFL and neighbouring Swiss lab CSEM have also developed a tandem solar cell with a record efficiency of 29.2% that combines a perovskite solar cell with a textured silicon solar cell.
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One obstacle was finding a way to evenly coat the textured silicon surface used in commercial silicon cells to minimise light reflection with a thin film of halide perovskites.
The team at the Photovoltaics and Thin Film Electronics Laboratory (PV-lab), led by Christophe Ballif, enhanced an existing method with highly transparent window layers, resulting in tandem solar cells with an efficiency of 29.2% on a surface of 1 cm2. This yield was certified independently by the Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) in Germany, and sets a new world record for a fully textured perovskite-silicon device.
The team sees a clear path to achieving yields of beyond 30% by taking advantage of the high current provided by the silicon texture.
“Several years of R&D are still needed to bring such technology and manufacturing processes to market,” said Ballif. “A big challenge will be developing solar cells that can remain stable on our rooftops for more than 25 years. But the higher efficiency we demonstrated without changing the front texture will be very attractive for the photovoltaics industry.”
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