Researchers at nanoelectronics research center imec of Leuven, Belgium (a partner in Solliance and EnergyVille), Germany's Karlsruhe Institute of Technology (KIT), and ZSW (Zentrum für Sonnenenergie- und Wasserstoff-Forschung — or Center for Solar Energy and Hydrogen Research — Baden-Württemberg) in Stuttgart, Germany, have fabricated a tandem multi-junction thin-film solar module stack consisting of perovskite and copper indium gallium selenide (CIGS) with a solar energy conversion efficiency of 17.8%, surpassing for the first time the highest efficiencies of separate perovskite and CIGS modules.
The 3.76cm2 stacked module implements a fully scalable device concept: both the perovskite top module and the CIGS bottom module feature a monolithic interconnection scheme (using seven and four module cell stripes, respectively. The result is a reduction in area loss of less than 8% for both technologies.
The higher energy part of the spectrum is harvested in the semi-transparent perovskite module on top, while the light with lower energy passes and is harvested in the bottom CIGS cell. As a result, the prototype shows an unprecedented power conversion of 17.8%, outperforming the record 15.3%-efficient upscaled perovskite module reported by imec as well as the highly efficient stand-alone upscaled CIGS module of ZSW (with efficiencies nearing 15.7%).
"This result was achieved through close and intricate collaboration leveraging the expertise of the three partners," says imec's head of thin-film PV research Dr Tom Aernouts. "Imec's expertise in perovskite technology was underscored by the use of a perovskite top module in these stacked solar modules."
According to Dr Ulrich Paetzold, head of the research group at KIT, the result is just a starting point, with more results to come in the next few years such as perovskite/CIGS multi-junction solar modules surpassing efficiencies of 25%. Paetzold's Helmholtz Young Investigator group (in KIT's Institute of Microstructure Technology and the Institute of Light Technology) is focusing on the optics in multi-junction perovskite solar modules and will develop further specialized nanophotonic materials for these devices.
Finally, ZSW contributed its expertise in CIGS solar modules. ZSW holds the record for CIGS solar cell efficiency of 22.7%. "This success is an elegant way of combining the advantages of two highly advanced thin-film technologies," comments professor Michael Powalla, member of the board and head of the Photovoltaics Division at ZSW.
The module and technical details were presented by imec's Dr Tom Aernouts, KIT's Dr Ulrich Paetzold and ZSW's Dr Erik Ahlswede on 26.
