Plants have been in the energy business for hundreds of millions of years. Every leaf is essentially a tiny solar panel, turning sunlight into fuel through a process called photosynthesis. Now, scientists in South Korea have figured out one of the secrets behind how plants do it so well — and their discovery could help humans build better solar panels and clean energy machines of our own.
A team at Sungkyunkwan University, led by chemistry professor Taeyeon Kim, working alongside researchers from Yonsei University, has uncovered a new principle for controlling charge transfer in organic semiconductors — the tiny molecular machines that could power the next generation of solar cells and artificial photosynthesis devices. Their findings were published in the journal Nature Communications.
The researchers focused on a special molecule called perylene bisimide, or PBI for short. PBI is good at grabbing electrons, which makes it useful for solar energy devices. But here's the tricky part: when these molecules cluster together in dense stacks, it becomes hard to study exactly how the surrounding environment affects their ability to move energy around.
To solve this, Kim's team built a special platform that let them change the surrounding liquid without disturbing how the molecules were stacked. They then used ultrafast lasers — so fast they operate on a scale of one quadrillionth of a second — to watch what happened inside the material.
What they discovered was surprising. Depending on the type of liquid around the molecules, the way charges moved through them changed completely. In liquids like oil, with low polarity, charges tunneled through energy barriers the way tiny quantum particles do. In more polar liquids like water or alcohol, charges instead rode along with the swaying movements of surrounding molecules. The team called this a "mechanism crossover" — a complete switch in how the system worked, triggered simply by changing the environment.
The researchers also found they could control how far light energy traveled inside the material. By adjusting the solvent, they stretched the effective travel distance from 35.9 nanometers — about one-thousandth the width of a human hair — all the way to 98.8 nanometers. Longer distances mean less energy lost before it can be used.
Kim said the study isolated the effect of the electrical environment without altering the molecular structure, revealing a fundamental principle that could guide the design of cleaner, more efficient energy devices. "We expect this to provide integrated molecular design guidelines that can maximize the efficiency of environmentally friendly future energy devices such as organic solar cells and artificial photosynthesis systems," Kim said.
For anyone hoping for cleaner ways to capture sunlight, this discovery offers a new tool — borrowed from nature, then turned into something entirely human.