Solar energy technologies based on perovskite materials have been heralded for their efficiency gains and potential for lower cost manufacture. But a recent study shows that even very small defects in these devices can severely limit their durability. A team led by Mike McGehee at the Renewable and Sustainable Energy Institute (RASEI) of the University of Colorado Boulder, in collaboration with scientists from the National Renewable Energy Laboratory (NREL), has investigated how microscopic pinholes and contact-layer irregularities in perovskite solar cells lead to failure under reverse bias. Their findings, published in Joule, clarify a mechanism that had been unclear, and suggest paths toward more stable cell architectures.
Johnson, S., Morales, D., Fremouw, K., Gould, I. E., Borsa, T., Johnston, S., Palmstrom, A., DeCrescent, R. A., & McGehee, M. D. (2025). How non-ohmic contact-layer diodes in perovskite pinholes affect abrupt low-voltage reverse-bias breakdown and destruction of solar cells. Joule, 102102. https://doi.org/10.1016/j.joule.2025.102102
In solar panels, when one cell becomes shaded (or otherwise stops producing power), the other cells in the string continue to generate current. That current has to flow through the shaded; or non-producing; cell, which pushes that cell into a condition called reverse bias. Under reverse bias, that cell is forced to carry current in the opposite direction from that intended, and this can heat up parts of the cell, causing damage. This behavior is well known in silicon photovoltaics, where bypass diodes are used to protect shaded cells. But with perovskites, this solution has been less effective, partly because of material and fabrication constraints.
The McGehee / NREL study focused on how pre-existing defects; especially pinholes (tiny voids in the perovskite film) and thin spots; become the initial loci of damage when a cell is in reverse bias. By combining advanced imaging techniques, including electroluminescence (EL) imaging, scanning electron microscopy (SEM), laser-scanning confocal microscopy (LSCM), and video thermography, they were able to observe three phases: before reverse bias is applied; during the bias; and after damage occurs. These tools revealed that in defective regions (pinholes or thin perovskite) the material heats up disproportionately and then melts or breaks down, forming a short between layers. In contrast, defect-free small devices can withstand reverse bias much longer, showing that the defects, not just the reverse bias, are critical to the damage pathway.
Another important finding is that device architecture matters. The study shows that contact layers and their interfaces with perovskite play a role in how current flows in reverse bias, especially near defects. In particular, non-ohmic behavior emerges in contact layers near pinholes, which can amplify the local field and contribute to abrupt breakdown. That suggests that improving contact layer uniformity, choosing more stable contact materials, or otherwise managing interfaces could be key steps in making perovskite solar cells more robust.
Ryan DeCrescent researcher from the University of Colorado Boulder stated,
“These are complex systems, and it can be very hard to untangle what is going on”.
The scale of the devices in the experiment was also important. The team fabricated many small perovskite devices (each about 0.032 mm², roughly the width of two human hairs) to compare “nearly perfect” films (with minimal or no defects) to larger films where defects are much more likely. They found that the small devices with minimal defects did not show abrupt failure under the same reverse bias conditions, whereas larger or more defective ones did. This confirms that film uniformity at large scale is a significant obstacle for commercialization.
The implications are twofold. First, researchers seeking to improve perovskite solar cell lifetime must pay more attention to defect suppression during fabrication; pinholes, thin spots, irregular contact interfaces. Fabrication methods that yield more uniform films and better contact layers may reduce or delay failure under reverse bias. Second, aside from materials, module design and system-level protections (like bypass mechanisms, though they are more challenging for perovskites) may become necessary components of commercial deployments.
Still, several open questions remain. For example, how do these degradation mechanisms behave under partial shading (rather than full reverse bias), or in field conditions with temperature, humidity, and cycling? Also, what trade-offs will emerge when trying to improve film uniformity; do improvements in uniformity come at the expense of other properties, such as cost, manufacturability, or scale? And how to balance contact layer stability and interface chemistry so that long-term stability is achievable without overly complex fabrication processes?
In sum, this study does more than reveal a hidden failure mode in perovskite solar cells; it gives direction. By showing that defects such as pinholes and weak contact interfaces are the likely starting points for reverse bias breakdown, it provides concrete goals for both materials scientists and device engineers. If film quality and contact interfaces can be improved sufficiently, perovskite solar cells may better maintain performance under realistic shading and operational stress—bringing them closer to reliable, large-scale deployment.
Adrian graduated with a Masters Degree (1st Class Honours) in Chemical Engineering from Chester University along with Harris. His master’s research aimed to develop a standardadised clean water oxygenation transfer procedure to test bubble diffusers that are currently used in the wastewater industry commercial market. He has also undergone placments in both US and China primarely focused within the R&D department and is an associate member of the Institute of Chemical Engineers (IChemE).
