Ultrafast Charge Transfer and Upconversion in Zinc β-Tetraaminophthalocyanine-Functionalized PbS Nanostructures Probed by Transient Absorption Spectroscopy

We functionalize PbS nanocrystals with the organic semiconductor Zn beta-tetraaminophthalocyanine to design a nanostructured solid-state material with frequent organicinorganic interfaces. By transient absorption and fluorescence spectroscopy, we investigate the optoelectronic response of this hybrid material under near-infrared excitation to find efficient charge transfer from the nanocrystals to the molecules. We demonstrate that the material undergoes cooperative sensitization of two nanocrystals followed by photon upconversion and singlet emission of the organic semiconductor. The upconversion efficiency resembles that of comparable systems in solution, which we attribute to the large amount of interfaces present in this solid-state film. We anticipate that this synthetic strategy has great prospects for increasing the open-circuit voltage in PbS nanocrystal-based solar cells.