Enhanced quantum dot deposition on ZnO nanorods for photovoltaics through layer-by-layer processing

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Abstract
ZnO nanorods are coated with a conformal film of CdTe nanoparticles using a layer-by-layer (LbL) process. By increasing the number of CdTe layers the absorption of incident light increases at wavelengths lower than the absorption onset of the nanoparticles (650 nm). At the absorption peak of the nanoparticles, 50 layers of nanoparticles coated onto ZnO nanorods absorb 80% of the incident light. Annealing of the ZnO–CdTe composites leads to a small red-shift in this absorption onset, but does not destroy the quantum confinement of the nanoparticles. Solar cells are produced by filling the CdTe-coated nanorods with CuSCN or PEDOT:PSS, and tested under AM 1.5 illumination. Annealing of the LbL films is essential to reduce the series resistance of the cell. Annealed cells generate an open-circuit voltage of 120 mV and a short-circuit current density of 0.19 mA cm−2.