Role of perovskite top-cell’s bandgap on photovoltaic performance of 2T perovskite/CIGS tandem solar cells: An experimental study

Zohair Abbas^a^,^b, Damilola Adeleye^c, Radha Krishnan Kothandaraman^b, Saif Ali^a, Chiara Ostendi^a, Ayman Maqsood^c, Jakob Lauche^c, Marcel Handke^c, Guillermo Fariaz-Basullto^c, Denise Kruegel^b, Erica Magliano^a^,^d, Veronique Gevaerts^b, Valerio Zardetto^b, Iver Lauermann^c, Reiner Klenk^c, Christian A. Kaufmann^c, Aldo Di Carlo^a^,^d

^aC.H.O.S.E. (Center for Hybrid and Organic Solar Energy), Electronic Engineering Department, University of Rome Tor Vergata, Via del Politecnico 1, 00118, Rome, Italy.

^bTNO, partner in Solliance, High Tech Campus 21, Eindhoven, the Netherlands

^cPVcomB/ Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Schwarzschildstr.3, D-12489 Berlin, Germany.

^dIstituto di Struttura della Materia (CNR-ISM) National Research Council, via del Fosso del Cavaliere 100, 00133, Rome, Italy.

Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV26)

Uppsala, Sweden, 2026 May 18th - 20th

Organizers: Gerrit Boschloo, Ellen Moons, Feng Gao and Anders Hagfeldt

Oral, Zohair Abbas, presentation 076
Publication date: 11th March 2026

Tandem solar cells based on thin-film photovoltaics offer substrate flexibility and a potentially cost-effective alternative to crystalline silicon. In particular, monolithic two-terminal tandems combining a wide-bandgap perovskite top cell with a Cu(In,Ga)Se 2 2 (CIGS) bottom cell are a compelling route to high-efficiency thin-film modules. Optical simulations have proposed suitable perovskite bandgap windows for current matching, yet the bandgap dependence has rarely been examined experimentally in a controlled, like-for-like device platform. Here we systematically fabricate and compare perovskite top cells with three bandgaps and integrate them monolithically onto CIGS bottom cells to identify practical bandgap–architecture combinations for high performance. Guided by optical–electrical co-design, we implement bandgap-resolved absorber compositions together with interface and surface-passivation strategies that expose the trade-offs among voltage, current and fill factor in the tandem configuration. Monolithic perovskite–CIGS tandems built from the selected top‑cell architecture demonstrated power‑conversion efficiencies reaching 25% on 1 cm² active area, placing the performance close to the state of the art efficiency reported on the same area scale. Beyond a single champion, the comparative dataset clarifies when the tandem becomes top-limited and shows that higher-bandgap top cells can partially compensate reduced current through improved fill factor and voltage. By explicitly testing multiple perovskite bandgaps rather than assuming a single target composition, we provide experimentally grounded design rules for top-cell selection and interface engineering in monolithic perovskite–CIGS tandems.

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