New tandem solar cell delivers a certified efficiency of 29.2%

This achievement was made possible by combining a perovskite solar cell with a textured silicon solar cell.


Silicon-based solar cells have a variety of applications but have limited power-conversion yields: maximum yields of around 23–25%. These limitations can be solved by combining silicon with a complimentary solar cell that absorbs and utilizes the blue-green part of the solar spectrum more efficiently, forming a “tandem.”

Among the various materials that can be utilized for the tandem, halide perovskites have lately proven to be the most effective at increasing silicon efficiency without significantly increasing fabrication costs. However, one hurdle was finding a way to evenly coat the silicon surface – intentionally rough or textured – with a thin film of halide perovskites.

To reduce light reflection, a textured surface is used. All commercially available crystalline silicon cells already have this type of technology.

Scientists at EPFL‘s Photovoltaics and Thin Film Electronics Laboratory (PV-lab), led by Christophe Ballif, developed a method in 2018 to grow perovskite layers on textured silicon uniformly. Their proof-of-concept devices were shown to achieve an efficiency of 25.2%.

Scientists have improved the perovskite crystallization process and developed highly transparent window layers, resulting in tandem solar cells with an efficiency of 29.2% on a surface of 1 cm2.

Although, this is an immediate step. Scientists have seen a clear path to achieving yields beyond 30% by taking advantage of the high current provided by the silicon texture.

Ballif said“Several years of R&D are still needed to bring such technology and manufacturing processes to market. 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. The discovery shows high promise to cut the power generation cost per kWh, by producing more energy on the same area.”

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