Can a tiny wire make solar cells more efficient?

If you cycle through any Dutch neighbourhood, chances are you’ll see rooftops full of solar panels. They look simple: black rectangles catching sunlight and turning it into electricity. But inside each of those panels is a delicate piece of technology. That piece of technology is what Jonas Valentijn, PhD researcher at UT, is trying to improve.

Solar cells still reflect away light

A solar panel is made up of many individual solar cells: thin slices of silicon covered with a grid of microscopic metal lines. These lines collect the electricity that the cell produces. But there’s a catch. Those metal lines also block sunlight. “Even in today’s high-efficiency solar cells, one of the biggest losses still comes from the front grid,” Jonas says. “The lines are flat, so they reflect light away from the cell. That’s wasted energy.” For an industry racing toward maximal efficiency, even losing a few percent to these tiny lines is a big deal.

Pull a wire upward

How do you make those metal lines less wasteful? Jonas is exploring the possibility of shaping the metal lines into tiny triangles rather than flat strips. A triangular shape can bounce light back into the solar cell rather than reflecting it away. That could mean 0.5 to 1% absolute efficiency gained, which is massive for the solar industry.

But there’s a reason no one is doing this yet. “You can’t just print triangles at this scale with the usual manufacturing process,” Jonas explains. “The current methods give you flat, blocky lines. You have almost no control over the shape.” So they needed a new way to make these ultra-small metal contacts. Enter the method that sounds like something from a craft workshop rather than a high-tech lab: string printing.

String printing is full of potential

The idea is simple: take a hair-thin wire, coat it in silver paste, press it onto a solar cell and slowly pull it upward. “As you lift the wire, it leaves behind this tiny triangular trail of metal paste,” Jonas says. “The method works by stretching the paste using the correct balance of forces.” It sounds straightforward. In reality? Not even close. A human hair is about 80 microns thick. Jonas works with wires that are 10 microns. At that scale, particle size, adhesion, tension, temperature; everything matters. “If you pull too fast, the triangle collapses. Too slow, and it spreads out,” Jonas says. “The paste behaves differently depending on pressure, viscosity. It’s a whole landscape of parameters.”

Together with TCO (Techno Centre for Education and Research) workshops, the team built a fully programmable prototype machine. It can move with nanometre precision, adjust withdrawal speeds, test different wires and pastes, and create repeatable patterns. “It’s basically a lab-sized version of what a solar factory would need someday,” Jonas explains. And for the first time, the team can reproducibly print contact lines that actually work on real solar cells and outperform today’s standard ones.

Where the research stands now

After a year of experimentation, Jonas now has a setup that can print consistent triangular contacts on small test cells. “The next step is printing on real, high-quality solar cells from our partners,” he says. “Then we’ll measure how much efficiency we actually gain under a solar simulator.” They’re also exploring how the contacts behave once a protective layer of glass and encapsulation is added, the way real solar panels are built. If all goes well, this method could be scaled into a pilot production line. “Whether it’s commercially viable is a bigger question,” Jonas says honestly. “That depends on cost, speed, materials… but understanding the process is the first big step.”

What does this mean for people with solar panels?

For homeowners: probably nothing dramatic. Your next solar panel won’t suddenly double in output. But for solar farms, manufacturers, and countries chasing renewable energy targets? A 1% efficiency boost is massive. “On a household level, you won’t notice,” Jonas says. “But for big solar parks or national production, every fraction of a percent translates to huge gains.” Then there’s material use. Solar panels currently rely heavily on silver, one of the most expensive materials in the cell. Jonas’s method could help reduce that or even support the switch to cheaper metals like copper in the future.

“It looks simple, just pull a wire up,” he says. “But everything is connected. Materials, shape, physics, industry requirements… it’s like solving a very technical puzzle.” With the world rushing toward cleaner energy, even tiny improvements can ripple outward. A slightly better front grid can boost the impact of every solar farm, rooftop system, and climate target. “It’s a small detail,” Jonas says. “But small details add up. If we want the best possible solar cells, we need to look at everything, even the parts you barely see.”