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A team at The Hong Kong Polytechnic University (PolyU) has created a new perovskite-organic tandem solar cell that keeps working well even when part of it is shaded.
According to their study, these thin-film solar cells held onto over 90 percent of their original efficiency after being exposed to a harsh reverse bias of minus 40 volts, which usually harms standard thin-film solar cells.
When trees, clouds, buildings, or even birds block sunlight, solar panels can experience reverse-bias stress. This negative voltage lowers electricity output and can permanently damage thin-film solar cells. The PolyU team says their new design is much more resistant to this issue, making the technology more practical for real-world use.
Hidden defects trigger solar cell damage
Thin-film solar technologies like cadmium telluride, copper indium gallium selenide, perovskite, and organic solar cells are popular because they are light, flexible, and cost less to make. But they all have trouble when part of the panel is shaded.
Under these conditions, shaded cells can create negative voltage that stresses the material. Because these solar cells carry both electrons and ions, being under reverse-bias for too long can lower their performance and eventually cause damage. Making them more resistant to reverse bias is key to making them last longer.
The researchers looked closely at organic solar cells, since how they react to reverse-bias conditions is still not well understood, even though their efficiency has improved a lot in recent years.
Professor Li Gang, chair professor of energy conversion technology in PolyU’s Department of Electrical and Electronic Engineering, said, “We have achieved important advances in the stability of OSCs and POTSCs under challenging reverse-bias conditions. Our research makes breakthrough contributions to the understanding of both device operation and durability in organic and perovskite solar technologies.”
Researchers identify source of reverse-bias failure
The team discovered that damage comes from defects called deep trap states in the bulk heterojunction, which is the layer where electricity is made. These defects trap electrical charges, which lowers efficiency and makes permanent damage more likely during reverse-bias operation.
To address the issue, the researchers suppressed isolated acceptor clusters in the donor-acceptor mix area of the solar cell. This cut down the number of deep trap states and made the devices much more durable.
As a result, the new organic solar cells could handle a breakdown voltage of more than minus 35 volts. This means they can take reverse bias up to that level without lasting damage, setting a new standard for stability and efficiency in organic solar cells.
Tandem cells protect the perovskite layer
The study also showed that the improved organic solar cells protect the perovskite layer in n-i-p inorganic perovskite-organic tandem solar cells. They do this by stopping reverse tunneling, which is when reverse current harms the device during shading.
Even after being exposed to minus 40 volts, the tandem solar cells kept more than 90 percent of their original efficiency.
The devices also showed strong long-term stability. After running at minus 20 volts for 12 hours, they kept 90 percent of their starting efficiency. They held onto 97 percent of their efficiency after working at minus 4.5 volts for 2,000 hours, or about 83 days. The researchers say these results are better than what current thin-film solar technologies can do.
Results build on earlier efficiency gains
This new work builds on the team’s earlier research published in Nature Energy in 2025. In that study, they developed n-i-p inorganic perovskite-organic tandem solar cells with a power conversion efficiency of 25.9 percent, which was independently certified at 25.1 percent, using bottom-contact modulation.
In this new study, the tandem solar cells reached over 26 percent power conversion efficiency and became much more resistant to reverse-bias stress. This brings the technology closer to being used in real-world solar modules.
“The exceptional reverse-bias stability under shading conditions has been vividly demonstrated in scalable perovskite-organic tandem solar cell minimodules. This marks a significant leap forward, paving the way for a sustainable and efficient future powered by renewable energy systems,” Li added.
The new study is published in the journal Nature Materials.
