Targeting Both Solar Power and Green Hydrogen Production... UNIST Develops Interface Control Technology [Reading Science]

Perovskite-Organic Tandem Solar Cells Achieve 25.1% Efficiency
Solar-to-Hydrogen Conversion Efficiency Reaches 7.7%

A next-generation solar interface technology has been developed that not only increases solar power generation efficiency but can also be applied to hydrogen production using solar energy.

On March 17, Ulsan National Institute of Science and Technology (UNIST) announced that a research team led by Professor Jinyoung Kim and Professor Dongsuk Kim of the Graduate School of Carbon Neutrality, and Professor Seungjae Shin of the Department of Energy and Chemical Engineering, has developed a technology that simultaneously enhances both the performance and stability of perovskite-organic tandem solar cells by controlling the chemical state of self-assembled monolayers (SAMs).

Performance of perovskite organic tandem solar cells and photoanode devices with deprotonated self-assembled monolayers (SAMs) applied. Provided by the research team

Perovskite-organic tandem solar cells are next-generation solar cells that stack two types of solar cells absorbing different wavelengths of light, one on top of the other, to convert sunlight into electricity more efficiently. However, in tandem structures, if the interface between the transparent electrode and the perovskite layer is unstable, charge transfer is hindered and long-term stability is compromised.

The research team proposed a method to control the chemical state of "2PACz," a self-assembled monolayer material formed at this interface. By using potassium carbonate (K₂CO₃) to partially remove hydrogen ions from the phosphate groups of 2PACz molecules, the molecules become negatively charged, allowing them to bind more strongly to the ITO transparent electrode in this state.

The deprotonated 2PACz (2PACz-K) formed through this process adheres more stably to the electrode surface, preventing it from being washed away by solvents during solar cell fabrication and forming a uniform interface.

Perovskite solar cells using this technology demonstrated higher voltage and improved charge transport characteristics. Based on this, the perovskite-organic tandem solar cells achieved a maximum power conversion efficiency of 25.1% and an open-circuit voltage of 2.23V. Furthermore, under maximum power point tracking (MPPT) conditions, the cells maintained over 80% of their initial performance even after 220 hours of continuous operation, exhibiting strong stability.

Research team photo. From left to right: Professor Jinyoung Kim, Professor Seungjae Shin, Professor Dongseok Kim, Dr. Jungun Son, Researcher Haeun Koo, Dr. Woojin Lee. Provided by UNIST

The research team also applied this interface technology to photoelectrode devices that use sunlight to split water and produce hydrogen. The tandem photoelectrodes incorporating the technology exhibited high photovoltage, enabling water splitting reactions without any external voltage, and achieved a maximum solar-to-hydrogen conversion efficiency of 7.7%.

Professor Jinyoung Kim of the Graduate School of Carbon Neutrality at UNIST stated, "We have improved both the performance and stability of solar cells through a strategy to control the chemical state of the interface at the molecular level," adding, "This could be used in the development of next-generation energy systems that combine solar power generation with green hydrogen production."

This research was led by Dr. Jungun Son, Haeun Koo, an integrated master's and doctoral program researcher at UNIST, and Dr. Woojin Lee as first authors. The results were published in the academic journal Energy & Environmental Science in the field of energy chemistry on February 5. The study was supported by the Ministry of Science and ICT and the National Research Foundation of Korea.

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