Printable Solar-Cell Material Reaches a Milestone
A new way of manufacturing printable organic solar cells could eventually lead to new kinds of low-cost, cheap, and flexible solar panels.
The work is being led by Alan Heeger, who shared the Nobel Prize in Chemistry with Guillermo Bazan in 2000 for developing the kind of conductive polymers that are already used to make plastic solar cells and organic light-emitting diodes. Both Heeger and Bazan are professors of chemistry at the University of California, Santa Barbara.
Polymer solar cells are inefficient compared to silicon solar cells, but they are much cheaper to make. Organic materials—whether made of polymers or so-called “small molecules,” which are organic compounds with a low molecular weight—can be made into inks and printed over large areas. They’re also lightweight and flexible, which makes them promising for applications like rooftop installations or solar-cell patches for charging portable electronics.
Using a new small molecule designed by Bazan, Heeger built a solar cell that converts 6.7 percent of the light energy that strikes it into electricity. Bazan expects to reach 9 percent efficiency within a year. Although efficiencies in lab tests tend to be much greater than those in a manufactured cell, this would put these materials on par with the best polymer solar cells on the market.
Until now, most efforts to improve the performance and cost of organic solar cells have focused on developing new polymer materials.
Bazan used a combination of theory and trial-and-error to develop the new small molecule material. He started by optimizing its electrical properties, so that the molecule would be able to support the high current and voltage needed to get power out of a solar cell. It’s especially tricky to create a small-molecule material that makes a good film; while polymers are long and get tangled into a stable film, small molecules don’t tend to make the kind of planar films needed to make a layer in a solar cell.