EPFL Scientists develop 25.2% efficient perovskite/silicon tandem cell

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Scientists based at EPFL and the Swiss Center for Electronics and Microtechnology (CSEM) have outlined a process for the deposition of a perovskite layer onto a silicon solar cell, creating a tandem cell. The scientists say that their process overcomes several difficulties with combining the two materials; and could lower the cost of tandem cell production.

The process, described in the paper Fully textured monolithic perovskite/silicon tandem solar cells with 25.2% efficiency, published in the journal Nature Materials, has already allowed the researchers to develop a cell with 25.2% conversion efficiency, and they state that the process “has the potential to achieve power conversion efficiencies above 30% at reasonable cost.”

The paper explains that when a perovskite material is deposited onto silicon, the material tends to accumulate in the ‘valleys’ of silicon’s pyramid-like surface, leaving the peaks uncovered, which can lead to short circuits. Common approaches to solving this problem have involved polishing the silicon to make its surface smoother. However, as the paper’s abstract points out, “This concession leads to higher potential production costs, higher reflection losses and non-ideal light trapping.”

To better solve the problem, the EPFL/CSEM researchers created an inorganic base layer to cover the silicon pyramids, then deposited the organic perovskite compound onto this. They say their process has been designed to allow easy adoption into crystalline silicon cell production lines, though it is also acknowledged that more work is needed, particularly with regard to the cell’s long-term stability, before the process could be realized commercially.

Specialist perovskite company, Oxford PV recently achieved a record 27.3% cell efficiency using its perovskite/silicon tandem technology, and states that it expects to launch a commercial module based on this by 2019.