Targeted surface treatment improves the molecular contact and increases the efficiency and stability of perovskite solar cells.

Perovskite solar cells are a rapidly advancing photovoltaic technology that has seen a dramatic rise in power conversion efficiency in recent years. A key driver of this progress is the use of molecular charge-selective contacts—ultrathin interlayers only a few nanometres thick—that replace conventional bulk transport materials. These molecular layers play a critical role in extracting and transporting electrical charges at the electrode interface.
Despite their importance, the structural organization and surface coverage of these molecules on transparent conductive oxide substrates are not yet fully understood. This lack of understanding is particularly critical, as the interface between the electrode and the molecular interlayer governs charge transfer efficiency and strongly influences both device performance and long-term stability.
In Advanced Energy Materials, researchers from LMU Munich present a streamlined strategy to overcome these interface challenges. Using a newly developed surface treatment, they managed to improve the molecular contact, yielding tangible gains in the efficiency, reproducibility, and stability of devices. Rather than focusing solely on developing new molecular materials, this approach highlights the importance of preparing the electrode surface.

Surface chemistry as key to efficiency
The team led by Dr. Erkan Aydin, group leader at LMU’s Department of Chemistry and Pharmacy, developed a comparatively easy, solution-based method for treating the widely used indium tin oxide (ITO) electrodes. The goal of the researchers was to precisely tune the chemical and electronic properties of the surface such that the self-assembled monolayers (SAMs) that form the organic interlayer can bind optimally.
“We show that maximizing surface hydroxylation is not the key,” explains Rik Hooijer, who is the first author of the work. “Rather, a balanced ratio of different oxygen species yields more uniform and electronically favorable interfaces.” The results thus contradict a prevailing assumption in the field and open up new pathways for the targeted engineering of contacts in optoelectronic devices.

Better performance and reproducibility
The optimized interfaces deliver clear advantages across various solar cell architectures. Charge transport becomes more efficient, and the solar cell converts a greater share of incident solar energy into electrical energy. In addition, the distribution of performance values is much narrower. “Our treatment improves not only absolute performance but also enhances the lifetime of the molecular contact-coated substrates and the reliability of the devices,” summarizes Aydin. “This is decisive if we want to take the technology out of the lab and into real-world applications.”
The researchers also demonstrated that their method is compatible with a wide range of materials, fabrication processes, and cell architectures – from simple single-junction cells to tandem solar cells.
A further advantage is that the treated solar cells proved to be more robust under stress. In tests involving intense temperature cycling between −80 and +80 degrees Celsius – conditions such as occur in space – the cells demonstrated improved stability. “The enhanced resilience under extreme conditions makes our approach especially promising for applications beyond conventional uses, such as space travel,” says Aydin.

New prospects for material development
The study makes clear that the interface between the electrode and the active layer should no longer be viewed as a passive component. Instead, it functions as a critical parameter that substantially influences the performance of modern solar cells.
With the new approach, the LMU team provides a scalable, industry-compatible solution that can be integrated into existing fabrication workflows. In the long term, this could help make perovskite solar cells more efficient, stable, and market-ready.