A team of researchers from the Centre for Solar Energy and Hydrogen Research Baden-Württemberg (ZSW) in Stuttgart, Germany, has combined perovskite with copper indium gallium selenide (CIGS) to build a tandem solar module with an efficiency of 21% and above.

While the best performance attained with the tandem solar modules is just slightly higher than 22%, the institute claims to have already achieved an efficiency of up to 26.6% in smaller laboratory cells.

The team said their prototype, with an area of nine square centimeters, features scalable component architecture suitable for industrial manufacturing.

ZSW partnered with the Karlsruhe Institute of Technology (KIT) in this research initiative.

The tandem module is made of two solar modules sandwiched against each other and, as a result, delivers more electrical energy than conventional panels. The different active layers work together to increase efficiency by jointly making better use of the width of the solar spectrum than each single solar cell does on its own.

The institute said the tandem module is a promising next-generation technology to accelerate the rollout of photovoltaic systems that generate more solar power. Currently, the efficiency of silicon solar cells is fast approaching the practical limit of around 27%, and as it stands, tandem solar modules can increase the efficiency to well over 30%.

The researchers began by optimizing the submodules, wherein the top perovskite half-module had to be highly efficient and semi-transparent to allow enough light to pass through the bottom module. The team made several improvements to this end, including developing more transparent electrodes and enhancing the passivation of boundary layers.

The institute said their tandem structure outperformed individual cells or modules in terms of efficiency, demonstrating the superiority of tandem solar modules.

Benefits of tandem solar modules

Tandem solar cells that pair perovskite with CIGS offer benefits beyond high efficiency. This thin-film technology can also be deposited on plastic or steel films to make light, flexible modules that lend themselves to many more use cases.

They can be installed conventionally in solar parks and seamlessly integrated into vehicles and on factory roofs that cannot handle heavy loads. It also costs less to generate power with thin-film photovoltaic modules.

The institute’s experts used these thin-film technologies exclusively for their module. The bottom of the module is made of perovskite and CIGS.

The technology has been ramped up for mass production in earlier projects by the institute and industry experts. ZSW now aims to scale up further and develop tandem thin-film technology in a joint effort with interested industry clients.

Recently, another team of researchers from Northwestern University, the University of Toronto, and the University of Toledo claimed to have developed an all-perovskite tandem solar cell with a conversion efficiency of 27.4%, which is comparable with traditional silicon solar cells.

In October, researchers at the Swiss Federal Laboratory for Material Science and Technology claimed to have achieved an efficiency of 22.2% for CIGS flexible solar cells.