Nanoparticle-assisted high photoconductive gain in composites of polymer and fullerene

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Abstract

Polymer–inorganic nanocrystal composites1,2,3,4,5,6,7,8,9,10 offer an attractive means to combine the merits of organic and inorganic materials into novel electronic and photonic systems. However, many applications of these composites are limited by the solubility11 and distribution of the nanocrystals in the polymer matrices. Here we show that blending CdTe nanoparticles into a polymer–fullerene matrix followed by solvent annealing12 can achieve high photoconductive gain under low applied voltages. The surface capping ligand renders the nanoparticles highly soluble in the polymer blend, thereby enabling high CdTe loadings. An external quantum efficiency as high as 8,000% at 350 nm was achieved at −4.5 V. Hole-dominant devices coupled with atomic force microscopy images show a higher concentration of nanoparticles near the cathode–polymer interface. The nanoparticles and trapped electrons assist hole injection into the polymer under reverse bias, contributing to efficiency values in excess of 100%.

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Figure 1: Device structure, current density/voltage (JV) characteristics and absorption spectrum.
Figure 2: TEM images and external quantum efficiency.
Figure 3: Photocurrent density/voltage characteristic of different devices.
Figure 4: Tapping-mode AFM images of the polymer films.

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Acknowledgements

H.-Y.C. and Y.Y. acknowledge financial support from Solarmer Energy (grant no. 20061880) and the Air Force Office of Scientific Research (FA9550-07-1-0264). Help from Hyun Cheol Lee for the TEM images and valuable discussions with Gang Li from Solarmer Energy are also highly appreciated. H.-Y.C. is grateful to Wei Lek Kwan and Bao Lei for helping with the transient measurements.

Author information

H.-Y.C. conceived and performed the experiments and measurements. M.K.F.L. performed synthesis of CdTe nanoparticles and the capping ligands. G.Y. performed the AFM imaging. H.G.M. and Y.Y. conceptualized and directed the research project. All authors discussed the results and commented on the manuscript.

Correspondence to Yang Yang.

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