HZB hits 23.26% efficiency with CIGS-perovskite tandem cell

Helmholtz Zentrum Berlin (HZB) has set a new efficiency record of 23.26% with a perovskite/CIGS tandem cell measuring 1cm². That represents a significant improvement on the 21.6% achieved by HZB in February.

The new record means tandem cell efficiency is approaching the 23.35% record for a standalone 1cm² CIGS cell set in January by Solar Frontier. If scientists can demonstrate an efficiency gain for the tandem structure over a standalone cell, as has been achieved already with perovskite/silicon tech, the combination could garner significantly more interest.

Belgian research institute imec also achieved 24.6% efficiency with a perovskite/CIGS tandem device this year, with a cell measuring 0.5cm² and featuring a four-terminal structure, thus avoiding losses at the CIGS/perovskite interface.

The HZB record was presented this morning at the EU PVSEC conference in Marseille by scientist Steve Albrecht, who explained one of the key innovations that enabled the achievement was the development of an organic layer between the two cells, which reduced losses at the electrode separating the two active cell layers.

Microscopic image of HZB’s tandem PV cell and the reddish-colored self assembling monolayer between the CIGS and perovskite layers. Image: HZB

Image: HZB

The layer is based on organic carbazole molecules coupled with phosphonic acid and self assembled into a monolayer covering the rough surface of the semiconductors. “The SAMs [self-assembled monolayers] are strikingly simple and robust,” said Amran Al-Ashouri, a PhD student in Albrecht’s team. “This also allows them to be scaled up to industrial levels. In addition, they are compatible to a wide variety of substrates and their material consumption is extremely low.”

The group has filed two patents for innovations within the cell and says it hopes its work will accelerate progress toward viable, low cost perovskite PV technologies.