Measurement of electric current produced by a single molecule that absorbed light — Aiming for ultra-efficient solar cell that mimics photosynthesis

Q1. What inspired you to become a researcher?

A1. The thrill of finding an answer to a difficult question after lengthy pondering.

I liked reading when I was in elementary school. I remember one time I was absorbed in a book about a Math Olympiad that I found on a bookshelf. I cannot forget the thrill of that moment I came up with the solution after thinking about a single problem for days. I was totally fascinated. That stance remains unchanged today, and I continue seeking out difficult problems and thinking about them asleep or awake.

When I was 10 years old, at a school event, I wrote my dream for the future and put it in a time capsule. I had forgotten about it myself, but when I opened it at my coming-of-age ceremony, it said, "I want to be a researcher." I did job hunting in my junior year at college, but I had strong desire to work at a research laboratory in the future, so I entered a doctoral program. Before I knew it, I had fulfilled my childhood dream.

Q2. What research are you currently working on?

A2. Tackling the mystery of photoelectric conversion with STM

RIKEN has developed the world's first method to measure and visualize electric current produced by a single molecule that absorbs light with atomic-scale resolution. This measurement method provides new insights into the research on solar power generation and artificial photosynthesis. A unique trick for transforming a molecule in observation into a high-energy state by irradiating a wavelength-tunable laser was realized by combining with a scanning tunneling microscope (STM).

I encountered STM when I was a senior in college. At that time, I was interested in research on solar power generation, but I lost a game of rock-paper-scissors and was assigned to a nanoscience lab dealing with STM. At first, I was puzzled by the difference in research content, but I was attracted to STM, which makes me observe atoms with my own eyes, and I came up with the idea that it could be combined with solar power generation. However, it was technically difficult at the time and did not produce any results.

Later, I came up with an STM-based method to measure electric current generated by a single molecule upon light irradiation. Although it was difficult to develop, I continued making improvements, such as precise control of interaction between the STM probe and the light directed at molecules and finally succeeded in clearly capturing the photocurrent generated by a single molecule.

Currently, I am working on photoelectric conversion that mimics plant photosynthesis. At the photosynthetic reaction center, photoelectric energy conversion occurs at an astonishing efficiency of nearly 100%, but the mechanism remains a mystery. With the assistance of model photosynthetic systems by arranging molecules similar to photosynthetic pigments having been created, I am investigating the relationship between intermolecular distance/angle and energy conversion at atomic precision using STM. If I can elucidate this relationship, I think it will contribute to the development of highly efficient solar cells.

Q3. A message for those aspiring to become researchers

A3. Act immediately when inspiration strikes

The most exciting part of research is the moment when you keep challenging a big wall and break through it after trial and errors. It is important to keep thinking when faced with a difficult task, but without "inspiration," there will be nothing left to try next. I think it is important for researchers to keep having flashes of inspiration.

In 2025, I moved to the Institute of Science Tokyo to teach students. I tell my students to act immediately when inspiration strikes. Even if you get a new idea, time flies by and you may miss the opportunity.

Students sometimes say, "I am afraid of leaving the rails laid," but I want them to act without fear. Please make the most of your strengths and explore new avenues.

(Article: Yasuhiro Hatabe)