Researchers led by Edward H. (Ted) Sargent of the University of Toronto have built the first colloidal quantum dot solar cells certified to convert sunlight into electricity with greater than 10% power conversion efficiency (Nano Lett. 2016, DOI: 10.1021/acs.nanolett.6b01957). Although quantum dots have played a role in solar cells with efficiencies better than 11%, the nanoscopic spheres in those cases are used only as a light-absorbing material, says Oleksandr Voznyy, a researcher in Sargent’s group. The new cells use thin films of lead sulfide quantum dots deposited from solution as light-sensitive layers that also conduct electric charges between electrodes. Using these multitasking quantum dots unlocks simpler design approaches for this brand of solar cell, but the team will need to continue improving the efficiency to compete with or complement other promising materials, such as perovskites, Voznyy says. To beat the 10% benchmark, the researchers tweaked the surface chemistry of their quantum dots. The dots were initially capped with oleic acid to prevent clumping. But the organic compound traps charges, which undermines efficiency. By adding methylammonium iodide to the quantum dot solution before deposition, the team swapped out oleic acid for iodine, which inhibits charge trapping.