8th July 2022
New record solar cell efficiency
The first tandem perovskite-silicon solar cells to exceed 30% efficiency have been independently certified.
For the first time, an efficiency of greater than 30% for perovskite-on-silicon-tandem solar cells has been exceeded – thanks to a joint effort led by scientists from the Center for Electronics and Microtechnology (CSEM) and École polytechnique fédérale de Lausanne (EPFL), both in Switzerland.
Independently certified by the National Renewable Energy Laboratory (NREL) in the United States, these results are a boost to high-efficiency photovoltaics (PV) and pave the way toward even more competitive solar electricity generation.
Solar cell efficiency is defined as the percentage of energy from sunlight that can be converted via photovoltaics into usable electricity. Increasing the efficiency of solar cells is important for two reasons. In the short term, it is the best way to promote photovoltaics for applications where space is limited e.g., roofs, facades, vehicles, or even drones. In the long run, it is the most effective way to reduce the levelised cost of electricity.
However, all solar cells are fundamentally limited by the materials they are made from, which in turn affects the efficiencies they can achieve. The most adopted solar cell technologies to date are made with silicon. But despite silicon's success, its efficiency has a theoretical limit of around 29%. The current efficiencies for this technology stand slightly below 27%, leaving a very small margin for future gains.
In the race to innovate and exceed this limitation, scientists have added one (or more) complementary cell(s) to silicon, forming "tandem" cells. The higher-energy visible light of the sun is absorbed in the top cell, while the lower-energy infrared light is absorbed in the silicon cell placed at the rear of the tandem. Halide perovskites have been identified as an ideal partner for silicon, as they convert visible light more efficiently to electrical power compared to silicon alone, without overly increasing fabrication costs.
The Swiss researchers have succeeded in improving two kinds of perovskite-on-silicon tandems. Firstly, they adapted materials and fabrication techniques to deposit high-quality perovskite layers from solution on a planarised silicon surface, reaching a conversion efficiency of 30.9% for a 1 cm² solar cell. Secondly, working on a new version of a hybrid vapour/solution processing technique compatible with textured silicon surfaces, they produced a solar cell with power conversion efficiency of 31.3% (again on 1 cm²).
These results constitute two new world records: one for the planar and one for the textured device architecture. The latter approach provides a higher current and is compatible with the structure of current industrial silicon solar cells. The previous efficiency conversion record for perovskite-on-silicon tandem solar cells was set in 2021 by a team at the Helmholtz Zentrum Berlin, who achieved 29.8%.
"We have passed a psychological barrier," said Christophe Ballif, Head of the EPFL Photovoltaics Laboratory and CSEM's Sustainable Energy Center. "We have validated experimentally the high-efficiency potential of perovskite-on-silicon tandems. The 30% efficiency mark had already been achieved with other materials, namely III-V semiconductors. However, these materials and the processes used to make them are too expensive to sustain the energy transition – these devices are 1,000 times more expensive than silicon solar cells. Our results are the first to show the 30% barrier can be overcome with low-cost materials and processes, which should open new perspectives for the future of PV."
"These high-efficiency results will now require further R&D to allow their scaling up onto larger surface areas and to ensure that these new cells can maintain a stable power output on our rooftops and elsewhere over a standard lifetime," said Quentin Jeangros of CSEM. "Tandem perovskite-on-silicon technologies have been said to have the potential to exceed the 30% efficiency benchmark, but this is the first time this long-predicted potential has been demonstrated, which should hopefully pave the way for even cheaper sustainable electricity in the future."
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