Effect of Solvent Treatment on Solution-Processed Colloidal PbSe Nanocrystal Infrared Photodetectors

PbSe colloidal nanocrystals were used to fabricate infrared photodetectors. Low dark currents were obtained by using chemical treatments to improve the nanocrystal film quality and passivate traps in the nanocrystals. The effects of different nanocrystal capping groups, including oleic acid, octylamine, ethanedithiol, and benzenedithiol, on the nanocrystal film quality and the photodiode characteristics were studied. The spectral responsivities and quantum efficiencies of the photodetectors were also measured. We found that the physical quality of the films was very sensitive to the capping groups used for the nanocrystals as well as the specific exchange reactions. Specifically, the dithiol capping groups were found to enhance the rectification of the photodetectors and significantly reduce the dark current in the devices by effectively passivating the surface traps.