New quantum-dot recipe may yield more-efficient solar cells

Cadmium selenide (CdSe) quantum dots with a four-legged, or tetrapod, structure are particularly effective at converting sunlight into electrical energy, according to previously reported research, but chemical recipes for producing CdSe tetrapods are only 40% efficient at best. Last month, researchers at the Rice University (Houston, TX) Center for Biological and Environmental Nanotechnology described a 90% efficient recipe that also appears to offer “greener” chemistry and scalability for fabrication of tetrapod-based photovoltaic and electronic devices.

Upon incorporating quartenary ammonium salt (QUAT) compounds such as cetyl-trimethyl-ammonium bromide or didodecyl-dimethyl-ammonium bromide into the hot-injection-synthesis process, the research team observed 90% and 92% efficiencies, respectively, in tetrapod production. The use of QUATS also eliminates a selective precipitation purification step, as well as the need for costly alkylphosphonate ligands in the fabrication process. Charge interactions between QUAT molecules and quantum-dot surfaces are thought to be responsible for the efficiency improvements, but the process is not yet thoroughly understood. “Our work knocks down a big barrier in developing quantum-dot-based photovoltaics as an alternative to the conventional, more-expensive silicon-based solar cells,” said principal investigator Michael Wong. Contact Wong at [email protected].