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Fully Indium-Free Monolithic Two-Terminal Perovskite/Perovskite/Silicon Triple-Junction Solar Cells: Replacing All
Maryamsadat Heydarian1, Minasadat Heydarian1,2, Sadaf Ghasemi1
1Fraunhofer Institute for Solar Energy Systems, Heidenhofstrasse 2, 79110 Freiburg, Germany.
ACS Energy Letters
|June 19, 2026
Summary
Researchers developed the first indium-free triple-junction solar cell, replacing indium tin oxide (ITO) with zinc-doped tin oxide (ZTO) and aluminum-doped zinc oxide (AZO). This innovation maintains high efficiency while addressing indium scarcity in photovoltaic technology.
Area of Science:
- Materials Science
- Renewable Energy
- Photovoltaics
Background:
- Indium-based transparent conductive oxides (TCOs), like indium tin oxide (ITO), are crucial in silicon and perovskite/silicon solar cells.
- Indium scarcity presents a significant challenge for the widespread adoption of photovoltaic technologies.
- Perovskite/silicon triple-junction solar cells require multiple TCO layers for transparency and carrier transport.
Purpose of the Study:
- To develop the first fully indium-free perovskite/perovskite/silicon triple-junction solar cell.
- To address the critical raw material limitations associated with indium in TCOs.
- To demonstrate that indium-free TCOs can be implemented without compromising solar cell efficiency.
Main Methods:
- Replaced all four indium tin oxide (ITO) layers in a perovskite/perovskite/silicon triple-junction solar cell architecture.
- Utilized zinc-doped tin oxide (ZTO) as the primary indium-free TCO material.
- Incorporated aluminum-doped zinc oxide (AZO) interfacial layers for enhanced contact and transport in the silicon bottom cell.
- Optimized ZTO composition (lower ZnO fraction) for the top TCO to improve lateral transport.
Main Results:
- Successfully fabricated the first indium-free silicon-based triple-junction solar cell.
- Achieved comparable efficiency to devices utilizing indium tin oxide (ITO).
- Demonstrated effective replacement of ITO with ZTO and AZO for transparency, lateral transport, and low contact resistance.
Conclusions:
- Indium-free transparent conductive oxides (TCOs) are viable alternatives for perovskite/silicon triple-junction solar cells.
- Zinc-doped tin oxide (ZTO) and aluminum-doped zinc oxide (AZO) offer a sustainable solution to indium scarcity.
- This work paves the way for more cost-effective and scalable production of advanced solar cell technologies.
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