Near-Infrared-II Photodetectors Based on Silver Selenide Quantum Dots on Mesoporous TiO2 Scaffolds

Biosensing applications are driving an increase in demand for low-cost photodetectors with sensitivity between 1000 and 1400 nm. Recently, the sensitivity of Ag2Se colloidal quantum dot based devices in this wavelength range has been observed. In this work we make the first demonstration of an Ag2Se photodiode device with sensitivity in this entire range. By employing secondary phosphine to elevate the precursor reactivity, we achieved accurate size control of the Ag2Se nanocrystals with a distinct excitonic absorption peak. These nanocrystals were deposited from solution into a mesoporous TiO2 scaffold, similar to that used in dye-sensitized solar cells, to increase the light absorption and charge separation and reduce the exciton diffusion length. By incorporation of a suitable hole-transporting layer between the active layer and Ag anode, the resulting devices showed a responsivity of 4.17 mA/W at a wavelength of 1200 nm. These results demonstrate that Ag2Se colloidal quantum dots offer a low-toxicity route for low-cost fabrication of near-infrared photodetectors.