Solar panels often have to deal with shade from trees, clouds, buildings, or even birds.
While this may seem like a minor inconvenience, partial shading can seriously damage many types of thin-film solar cells by creating a harmful electrical condition known as reverse bias. Over time, this can reduce power output and shorten the life of solar panels.
Now, researchers at The Hong Kong Polytechnic University (PolyU) have developed a new type of solar cell that is far more resistant to this problem.
Their perovskite–organic tandem solar cells not only achieve high energy-conversion efficiency but also continue performing well even under extreme electrical stress caused by shading.
The findings were published in the journal Nature Materials.
Thin-film solar technologies, including perovskite, organic, cadmium telluride, and copper indium gallium selenide solar cells, are attracting attention because they are lightweight, flexible, and less expensive to manufacture than traditional silicon panels.
However, they all share a major weakness. When part of a solar panel is shaded, the affected cells can experience reverse bias, where electricity flows in the opposite direction. This creates negative voltage that can permanently damage the cells.
Professor Li Gang and his research team focused on solving this long-standing challenge.
The researchers discovered that much of the damage is caused by tiny defects inside the organic layer of the solar cell.
These defects, known as deep trap states, capture electrical charges that should be generating power. As a result, the cells become less efficient and more likely to fail under reverse bias.
To address this, the team redesigned the structure of the organic layer to reduce these defects.
Their improved design allows the cells to withstand reverse voltages greater than -35 volts without suffering permanent damage. This represents a significant improvement over previous thin-film solar technologies.
The researchers then combined the improved organic cells with perovskite solar cells to create advanced tandem devices. In this design, the organic layer helps shield the perovskite layer from harmful reverse current when the panel is partially shaded.
The results were impressive. Even after exposure to an extreme reverse bias of -40 volts, the tandem solar cells retained more than 90% of their original power-conversion efficiency. The cells also demonstrated excellent long-term durability. After operating continuously for 12 hours under a reverse bias of -20 volts, they still maintained 90% of their original performance. Even more remarkably, after 2,000 hours of continuous testing at -4.5 volts, they retained 97% of their initial efficiency, outperforming all previously reported thin-film solar technologies.
The new solar cells also achieved a power conversion efficiency of more than 26%, meaning they convert over one-quarter of incoming sunlight into electricity. This combines high efficiency with outstanding durability, bringing the technology closer to practical use.
The researchers believe their work provides important new insights into how electricity moves through thin-film solar cells under reverse-bias conditions.
By overcoming one of the biggest obstacles facing perovskite-based solar technology, the breakthrough could help create more reliable solar panels that continue working efficiently even when partly shaded, making renewable energy systems more durable and practical for everyday use.
