At the Helmholtz Center Berlin for Materials and Energy (HZB), a research team has set a new record for the efficiency of tandem solar cells. The solar cell combines the semiconductor materials perovskite and CIGS.
This tandem solar cell combines the semiconducting materials perovskite and CIGS and achieves a certified efficiency of 23.26 per cent. One reason for this success lies in the cell’s intermediate layer of organic molecules: they self-organise to cover even rough semiconductor surfaces. Two patents have been filed for these layers.
Perovskite-based solar cells have experienced an incredibly rapid increase in efficiency over the last ten years. The combination of perovskites with classical semiconductor materials such as silicon and copper-indium-gallium-selenide (CIGS) compounds in tandem solar cells promises low-cost, high-performance solar modules for the future. However, losses at the electrodes between the two semiconductors considerably reduce the efficiency.
Record efficiency: 23,26 per cent
HZB physicist Prof. Steve Albrecht and his team now successfully established novel electrode coatings that greatly reduce these losses. They could produce a monolithic tandem solar cell from perovskite and CIGS that achieved an officially certified efficiency of 23.26 per cent, which currently is a world record value. The tandem cell has an active area of one square centimetre and thus reaches another milestone, as perovskite CIGS tandem cells have so far been significantly smaller.
Self assembled monolayer
The contact layers consist of carbazole-based organic molecules coupled to phosphonic acid groups. These molecules arrange themselves into what are known as self-assembled monolayers (SAMs). These SAMs have highly favourable electro-optical properties and the self-assembly even leads to complete coverage of rough semiconductor surfaces.
Two patents filed
“The SAMs are strikingly simple and robust. 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”, explains Amran Al-Ashouri, PhD student in the Albrecht group and first author of the study. This work might further accelerate progress towards extremely inexpensive perovskite-based PV technologies. The group has now filed two patents and is currently in licensing negotiations.