Switchable photoconductivity of quantum dot films using cross-linking ligands with light-sensitive structures

This paper describes the use of a diarylethylene (DAE) ligand, which adopts structures that are sensitive to the wavelength of light, to cross-link films of CdSe quantum dots (QDs) within electrical junctions with photoswitchable conductivity. These QD-DAE films are deposited on indium-tin-oxide/poly(3,4- ethylenedioxy-thiophene):poly(styrenesulfonate) (ITO/PEDOT:PSS) electrodes and have eutectic Ga-In top-contacts. The photocurrent density of the cross-linked QD films is enhanced by a factor of 6.5 (averaged over all applied voltages) when the DAE ligand is switched from its open, non-conductive form (by illumination with 500-650 nm light) to its closed, conductive form (by illumination with 300-400 nm light). This enhancement is accomplished by changing the inter-particle electronic coupling, not the inter-particle distance. Identical QD films cross-linked with dibenzenedithiol ligands have a photoconductivity that is insensitive to the wavelength of light.