Researchers from Solliance, a partnership of R&D organizations from the Netherlands, Belgium and Germany, and the Energy Research Centre of the Netherlands (ECN) report a 26.3 percent conversion efficiency for a perovskite top layer mechanically stacked on a crystalline silicon bottom cell. The device features ECN’s proprietary metal-wrap-through silicon heterojunction design.

The tandem perovskite solar cell combines good cell efficiency with a very high near infrared transparency of 93 percent, an increase of 3.6 percentage points over the efficiency of the directly illuminated silicon cell laminate. A semi-transparent top cell was combined with a 6-inch size crystalline silicon cell of 22.7 percent encapsulated cell efficiency. This bottom cell contributes 9.9 percentage points to the tandem cell efficiency, according to ECN.

An extremely high transparency was achieved for the top electrode, despite the low temperature process window, by optimizing the indium tin oxide (ITO) composition and deposition conditions, and by careful design of the anti-reflection coating. The ITO, with a sheet resistance as low as 40 Ohms per square, was used to fabricate a perovskite photovoltaic cell with an average transmittance in the relevant near-infrared wavelength range (800 – 1200 nm) of 93 percent. This is significantly higher than the state of the art, which is below 85 percent.

The active area of the tested semi-transparent perovskite cell was 0.09 cm². The technology has been scaled to 30x30 cm² demonstration modules by use of sheet-to-sheet spatial atomic laser deposition and laser interconnection of thin film cells.

ECN now seeks to further optimize the bottom cells and the module integration to improve conversion efficiency and reliability.

Transmittance curve of the semi-transparent perovskite cell (black line) and the measured external quantum efficiency of the silicon cell (red circles) when filtered by the semi-transparent perovskite cell. Source: ECN