Professor Tanenbaum in the lab

What was once a rare sight is now becoming more common: solar panels on the roofs of homes across the country. While solar technology has improved and is seeing exponential growth as an industry, Pomona College Professor of Physics David Tanenbaum notes there are a few factors that limit production at a mass scale globally. Tanenbaum and his student researchers are working to improve this by focusing on one important factor: the cost it takes to produce solar cell panels.

Tanenbaum explains that today’s solar panels, like microchips, are made with silicon, which requires a fairly expensive production process due to factors such as the need for high temperature processing of high-purity materials.

He compares the expense of making solar panels with silicon versus a less expensive organic material, to the manufacturing cost of making a flat-screen television to printing ink on paper. Imagine, he says, trying to cover the globe with expensive flat-screen televisions, that’s where solar cell technology is today. Now imagine covering the globe with the printed paper, and how much cheaper that would be and accessible – that’s where he wants to see solar technology go.

Solar Cell

Solar cell developed by Sabrina Li ’17.

To this end, Tanenbaum and his students are making organic solar cells using chemicals like P3HT, a poly(3-hexylthiophene) or polythiophene and PCBM, a fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester. They are experimenting with differing materials and processing techniques to make the cells.

“The main thing we want to get out of solar technology is a way to produce electricity. Everyone would benefit from electricity that is carbon neutral, and solar cells require no fuel stock: no gasoline, diesel or nuclear pellets. The sun is out there whether we take advantage of it or not,” he says. 

When it comes to solar cell technology, there are three main attributes: efficiency (how good the device is at converting sunlight into energy), production cost (how much it costs to produce cells and panels), and lifetime (how long the device will last).  

Current solar technology has good efficiency and a long lifetime, but the challenge still lies in the cost, he says.

“The idea is to bring the cost way down, even if it means the efficiency and lifetime is not so good,” he says. “The efficiency of the solar cell is maybe not perfect but the reality is there’s not a lot of waste. When you burn diesel fuel or natural gas to make electricity, you produce a lot of waste heat. You’re not wasting anything from the sun, just using a little bit for your advantage. The low cost allows us to displace natural gas, coal, all those things that have issues.

“In the grand scheme of things, we’d like to produce electricity at a low cost, and put electricity in isolated places relatively easily. In the U.S. everyone is connected to the electricity grid, but not everyone in the world is. You can’t build a nuclear power plant for a small amount of people, but solar energy can grow with the population.”

Tanenbaum has been working on this particular type of solar cell technology research for about eight years, and has had students in the laboratory helping since the beginning.

Sabrina Li ’17, a physics major, and Meily Wu Fung ’18, an environmental analysis major, are summer lab researchers through the Summer Undergraduate Research Program (SURP).

Li has been working with Tanenbaum since her first year at Pomona, and is planning a senior project that encapsulates what she’s learned in the lab thus far. “I’m looking at organic solar cells, they’re organic instead of silicon, and I’m looking at trying to optimize efficiency and lifetime.” Li experiments with different materials and processing techniques to make the cells.

This is Wu Fung’s first summer doing research at Pomona and she’s working on testing the aging of cells over time using cells created over the past three years in the lab that are still working today. “At the end of the day when we’re done making the cells, it’s really gratifying to measure them, and see what’s come of it.”

Tanenbaum will be on sabbatical for the 2016-17 academic year to continue his research on solar cell technology at the Catalan Institute of Nanoscience and Nanotechnology at the Autonomous University of Barcelona.