A major challenge in making solar cells more efficient is that a portion of the absorbed light energy is lost as heat. Now researchers at Columbia University in New York City have designed and synthesized a material that may enable polymer solar cells to recover some of that lost energy through a process called “singlet fission.”
In singlet fission, one absorbed unit of light generates two units of electricity rather than resulting in one unit of electricity and heat like in a conventional solar cell. “Critically, we show how this multiplication process can be made efficient on a single polymer chain, which is a type of plastic that can conduct electricity,” explains Dr Lüis Campos, assistant professor of chemistry at Columbia. Unlike previously reported fission materials, the expert says these polymers work efficiently while dissolved in liquids, a property that will be very advantageous in scaling the manufacturing process of a device to an industrial level.
The materials were designed and synthesized at Columbia, then analyzed using time-resolved optical spectroscopy at Brookhaven National Laboratory.
Now that Campos’ group has demonstrated the concept of multiplication — or singlet fission — for a large class of materials that utilize their design framework, the next major challenge will be to integrate these organic, carbon-based materials into solar cells and to harness the extra excitations in an operating device. “This may be in conventional bulk type solar cells or in third-generation concepts based on other inorganic (non-carbon) nanomaterials,” says the nanomaterials expert. “The dream is to build a solar cell that could be fully assembled using solution processing based on inorganic nanoparticles decorated with our organic fission materials.” Such a device would has the potential of breaking through the upper efficiency limit of 34% for single-junction cells.
In singlet fission — which Campos calls the electronic analogy of identical twins— both excitations are produced through multiplication residing on the same molecule. “A process that would normally produce a single offspring multiplies in early stages to produce two offspring,” he quips. “Our material guarantees identical twins with each fertilization.”
Written by Sandra Henderson, Research Editor Solar Novus Today