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Scientists at the City University of Hong Kong (CityUHK) have developed highly efficient, printable and stable perovskite solar cells to achieve carbon neutrality and promote sustainable development.

The new type of perovskite solar cell can be mass-produced at speeds comparable to newspaper printing, with a daily output of up to 1,000 solar panels. Thanks to their flexible, translucent characteristics, they can also be made into light-absorbing glass windows, realizing the concept of “urban solar farms” in cities with very tall buildings.

The research was led by the Lee Shau Kee Professor of Materials Science at CityUHK, Professor Alex Jen Kwan-yue, and the results were published in Natural energy.

The team demonstrated an effective strategy to improve the long-term stability of perovskite-organic tandem solar cells. The integrated cells retain over 90% of their original power conversion efficiency (PCE) after 500 hours of operation.

The operational stability of wide-bandgap perovskites has challenged scientists for more than a decade. The CityUHK research team tackled the problem with creative solutions in materials science. The team designed a series of organic redox mediators with suitable chemical potential for selective iodine reduction and metal oxidation.

After the perovskite device was integrated into the monolithic perovskite–organic tandem solar cell as a wideband subcell, the encapsulated tandem cell was subjected to 1-sun illumination (AM 1.5G spectrum, no UV filter).

It retained 92% of its original PCE after 500 hours of continuous operation at ~45 °C. The team also reported a record high efficiency of 25.22% (certified 24.27%). The device also showed good performance in humid air (70–80% relative humidity).

Dr. Wu Shengfan, a key member of the research team and the first author of the paper, said: “We were the first team to propose the use of redox and chemical synthesis methods to fundamentally solve the problem, effectively guaranteeing the stability of perovskite solar cells. “

He pointed out that CityUHK emphasizes critical thinking in training PhD students, mastering the cutting-edge topics in the field and understanding the biggest challenges they face and solutions to the most complex problems.

The research results will be transformed into practical applications through the start-up company HKTech Solar Limited, which will be managed by Dr Francis Lin, Professor Jen’s postdoctoral fellow at CityUHK.

Perovskite photovoltaics can absorb energy even in low indoor light and have mechanical flexibility. They can be integrated and applied in various scenarios, from large buildings and farms to various components of the Internet of Things.

The team also plans to set up a pilot production line with an annual output of 25 megawatts in Hong Kong within a year and a half and launch products for industry investors to test applications.