In a world first, perovskite-silicon solar cells break the 30% efficiency barrier

They just set two certified world records.
Derya Ozdemir
The new solar cellsD. Türkay, C. Wolff/EPFL

A collaborative effort led by EPFL’s Photovoltaics and Thin Film Electronics Laboratory in partnership with the famous innovation center, CSEM, has smashed through the efficiency record for tandem silicon-perovskite solar cells.

This is significant as the researchers have surpassed the milestone of 30 percent for the first time using low-cost materials and established two certified world records, pushing the technology beyond the limits of silicon.

"We have passed a psychological barrier," explains Christophe Ballif, Head of the EPFL Photovoltaics Laboratory and CSEM’s Sustainable Energy Center, in a press release. "We have validated experimentally the high-efficiency potential of perovskite-on-silicon tandems. The 30 percent efficiency mark had already been achieved with other types of 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 a thousand times more expensive than silicon solar cells."

"Our results are the first to show that the 30 percent barrier can be overcome using low-cost materials and processes, which should open new perspectives for the future of PV," he continued.

Breaking the limits and going beyond 

Solar cells are bound to the limits of whatever material they were made from. Today, silicon is the most widely used material for solar cells; however, despite its success, it does have its drawbacks as it has a theoretical efficiency limit of roughly 29 percent. This technology's current efficiencies stand at a little less than 27 percent, giving a very small margin for potential efficiency advancements.

To overcome this barrier, scientists have added more complementary solar cells to silicon, resulting in "tandem" solar cells. The press release explains that the sun's higher-energy visible light is absorbed in the top cell, while the lower-energy infrared light is absorbed in the silicon cell at the tandem's rear. Halide perovskites reportedly have been discovered as an appropriate silicon partner as they can convert visible light to electrical power more efficiently than silicon alone. Moreover, they don't increase fabrication costs significantly.

In the latest development, the researchers at EPFL and CSEM have succeeded in developing and improving the efficiency of tandem silicon-perovskite solar cells with high efficiencies using two different designs.

Tandem silicon-perovskite solar cells

The first consists of perovskite layers deposited from a liquid solution onto a flat silicon surface, which achieved a 30.93 percent efficiency for a 1 cm² test cell (0.2 in²).

The second one used a hybrid vapor and liquid solution approach to deposit perovskite onto a textured silicon surface, achieving a 31.25 percent efficiency for a 1 cm² solar cell.

According to the experts, more research is needed to determine how well the novel designs can be scaled up to greater surface areas. This could allow for scaling up to larger surface areas and ensure that these new cells can maintain a stable power output on our rooftops and elsewhere over a standard lifetime.

"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," Christian Wolff of EPFL said.

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