Imec has presented at the EU’s PVSEC conference a thin-film tandem solar cell consisting of a perovskite cell, developed by Imec itself in collaboration with EnergyVille and Solliance, and a lower cell CIGS developed by the ZWS. The cell resulting from this collaboration achieves a record efficiency of 24.6%.
The upper perovskite cell in the tandem uses light in the visible part of the solar spectrum while the light in the near infrared spectrum that passes through the perovskite cell is harvested by the underlying CIGS cell (Copper, Indian, Gallium and Selenium). In this way, the tandem cell significantly outperforms the independent perovskite and the CIGS cells.
In addition, both the perovskite and the CIGS cells are thin film solar cells, which enable the development of high efficiency flexible solar cells and integrated photovoltaic solutions (BIPV).
Additional technology improvements to be added soon will contribute significantly to the development of thin film tandem solar cells with efficiencies in excess of 30%.
The 4-terminal tandem consists of a perovskite solar cell placed on a CIGS cell, based on a fully scalable device concept to allow the industrial adoption of the process. The new record efficiency of 24.6% was achieved thanks to several innovations: firstly, the transmittance of the perovskite cell for near infrared light was improved through the addition of optical coupling layers in tandem and the optimization of the transparent electrodes. Second, the perovskite itself was optimized in terms of a wide bandwidth of 1.72eV for greater efficiency in tandem.
The CIGS cell with a size of 0.5 cm² was manufactured in the ZSW (Center for Solar Energy and Hydrogen Research Baden-Württemberg) high efficiency line, using all the optimized processes necessary for the preparation of recording devices. The result of the manufacturing process demonstrates the great success of the combination between both cells. Additional improvements to the technology that will be added soon will contribute significantly to the development of thin film tandem solar cells with efficiencies of more than 30%.
“We have worked on two types of tandem cells,” Tom Aernouts, researcher at imec / EnergyVille explains. “We have combined our state-of-the-art perovskite technology with lower silicon cells or CIGS. The advantage of CIGS is that it is a thin-film technology, as is perovskite, and that tandem cells can be manufactured in a wide variety of shapes and sizes. This makes it possible to use this technology in building-integrated photovoltaic applications. Future work will focus on improving the technology towards larger modules, and we will also study the development of solutions for 2-terminal cells due to their importance for the photovoltaic industry. Finally, what is important is the adoption of our solutions by our industrial partners. ”
“We owe record efficiency to two factors,” Michael Powalla, a board member and head of ZSW’s Photovoltaic Division notes. “On the one hand, the improved perovskite cell, on the other hand, one of the best efficiencies in the world for CIGS cells. There are several parameters of the CIGS cell that we can optimize in regards to its combination with the upper perovskite cell . Therefore, we expect even better efficiency values in the future, paving the way for further cost reduction. “