Researchers led by scientists at the University of California, Santa Barbara have developed a simplified process for making single-layer organic polymer solar cells.

The development portends a lower-cost method to power a new generation of wearable electronics and speed implementation of plastic electronics.

Polymer film on a glass substrate before immersion in a polyoxometalte solution. Credit: Christopher Moore/Georgia TechThe process simply involves briefly immersing organic semiconductor films in a doping solution at room temperature. Researchers say the technique could replace a more complex approach that requires vacuum processing, and has the potential to affect many device platforms, including organic printed electronics, sensors, photodetectors and LEDs, light-emitting diodes.

“Because the new process is simple to use, general in terms of applicability and should be configurable into mass productions, it has the potential to greatly accelerate the widespread implementation of plastic electronics, of which solar cells are one example,” says researcher Guillermo Bazan, director of UCSB’s Center for Polymers and Organic Solids. “One can see impacts in technologies ranging from light-emitting devices to transistors to transparent solar cells that can be incorporated into building design or greenhouses.”

Organic solar cells have been the under the microscope in research labs for years and have continued to experience slow but steady improvement in their power efficiency. They are unique within the context of providing transparent, flexible and easy-to-fabricate energy-producing devices.

Though polymer-based cells are still less efficient than commercial silicon-based cells, they require less energy to produce and can be more easily recycled at the end of their life span.

The newly developed method, which provides a way of inducing p-type electrical doping in organic semiconductor films, offers a simpler alternative to the air-sensitive molybdenum oxide layers used in the most efficient polymer solar cells, researchers say.

Thin films of organic semiconductors and their blends are immersed in polyoxometalate solutions in nitromethane for a number of minutes. The geometry of these new devices is unique as the functions of hole and electron collection are built into the light-absorbing active layer, resulting in the simplest single-layer geometry with few interfaces, researchers explained.

“High-performing organic solar cells require a multiple layer device structure,” says co-researcher Thuc-Quyen Nguyen, a professor in UCSB’s Department of Chemistry and Biochemistry. “The realization of single-layer photovoltaics with our approach will simplify the device fabrication process and therefore should reduce the cost.”

The initial lifetime testing of these single layer devices is promising, she says, and may help transform organic photovoltaics into a commercial technology.