Scientists at City University of Hong Kong (CityUHK) have made continuous breakthroughs in photovoltaic energy, developing highly efficient, printable and stable perovskite solar cells to achieve carbon neutrality and promote sustainable development.

The new type of perovskite solar cells can be mass-produced at a speed comparable to newspaper printing, with a daily output of up to 1,000 solar panels. Owing to their flexible, semi-transparent characteristics, they can also be made into light-absorbing glass windows, realising the concept of “urban solar farms” in cities with many high-rise buildings, such as Hong Kong and Shenzhen.

Led by Lee Shau Kee Chair Professor of Materials Science, Professor Alex Jen Kwan-yue, the research results were published in Nature Energy. The team demonstrated an effective strategy to enhance the long-term stability of perovskite-organic tandem solar cells. The integrated cells retain over 90% of their initial Power Conversion Efficiency (PCE) after 500 hours of operation.

The operational stability of wide-bandgap perovskites has been a challenge for scientists for over a decade. CityUHK research team addressed the issue with creative material science solutions. The team designed a series of organic redox mediators with appropriate chemical potentials to selectively reduce iodine and oxidise metals.

 

After the perovskite device was integrated into the monolithic perovskite-organic tandem solar cell as a wide-bandgap subcell, the encapsulated tandem cell was subjected to 1-sun illumination (AM 1.5G spectrum, without a UV filter). It retained 92% of its initial PCE after 500 hours of continuous operation at ～45 °C. The team also reported record-high efficiency of 25.22% (certified 24.27%). The device also exhibited good operational stability in humid air (relative humidity, 70–80%).

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 ensuring the stability of perovskite solar cells.” He pointed out that CityUHK emphasises critical thinking in nurturing doctoral students, advocating their mastery the most cutting-edge topics in the field, understanding of the biggest challenges faced, and solutions to the most complex problems.

“We are committed to creating societal impacts through innovative academic research, laying the foundation for Hong Kong and the Greater Bay Area’s competition in the emerging energy market,” said Professor Jen. He and his team also recently received a grant in the first round of funding from the Innovation and Technology Commission's Research, Academic and Industry Sectors One-plus Scheme (RAISe+ Scheme) for their new generation of printable high-efficiency perovskite photovoltaic modules. The research results will be transformed into practical applications through the start-up company HKTech Solar Limited, that will be managed by Dr Francis Lin, a postdoctoral student of Professor Jen.

Perovskite photovoltaics can absorb energy even under weak indoor light and have mechanical flexibility. They can be integrated and applied in different 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 annual output of 25 megawatts in Hong Kong within a year and a half and launch products for industry matching investors to test applications.