We report on bulk-heterojunction hybrid solar cells based on blends of non-ligand-exchanged CdSe quantum dots (QDs) and the conjugated polymer poly(3-hexylthiophene) with improved power conversion efficiencies of about 2% under AM1.5G illumination after spectral mismatch correction. This is the highest reported value for a spherical CdSe QD based photovoltaic device. After synthesis, the CdSe QDs are treated by a simple and fast acid-assisted washing procedure, which has been identified as a crucial factor in enhancing the device performance. A simple model of a reduced ligand sphere is proposed explaining the power conversion efficiency improvement

In this letter, we present a low-temperature synthesis route revealing a new type of ultrasmall CdSe nanoparticle family with exceptional narrow blue emissions between 437 and 456 nm and full width at half-maxima below 20 nm. Transmission electron microscopy characterization shows the uniformity of the nanoparticles, which have a diameter of 1.6 nm. After surface modification, the spherical particles assemble into nanowires, demonstrating their potential as building blocks for the generation of highly ordered superstructures. They can also be used as single source precursors for the synthesis of CdSe nanocrystals.

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Four kinds of magic-size CdS clusters and two different regular CdS quantum dots have been studied by x-ray total scattering technique and pair distribution function method. Results for the regular CdS quantum dots could be modelled as a mixed phase of atomic structures based on the two bulk crystalline phases, which is interpreted as representing the effects of stacking disorder. However, the results for the magic-size clusters were significantly different. On one hand, the shortrange features in the pair distribution function reflect the bulk, indicating that these structures are based on the same tetrahedral coordination found in the bulk phases (and therefore excluding new types of structures such as cage-like arrangements of atoms). But on the other hand, the longerrange atomic structure clearly does not reflect the layer structures found in the bulk and the regular quantum dots. We compare the effects of two ligands, phenylacetic acid and oleic acid, showing that in two cases the ligand has little effect on the atomic structure of the magic-size nanocluster and in another it has a significant effect. arXiv:1806.03274v1 [cond-mat.mes-hall]

The proper choice of the solvent is an important parameter in wet-chemical syntheses. Here, we highlight the use of 1-tetradecanol, a fatty alcohol, as an excellent solvent for the synthesis of high-quality zinc blende CdS quantum dots from cadmium laureate and tri-n-octylphosphine sulfide, the organometallic precursors. The as-prepared CdS quantum dots exhibit a defect-free (<1%) narrow blue emission at 452 nm with a full width at half-maximum of 18 nm (size distribution <5%) and photoluminescence quantum yield of 52% in comparison with quinine sulfate (reference dye). Our approach is simple and can be conducted as a one-pot reaction in air at temperatures below 200 °C. The key synthetic challenge is the preparation of the cadmium precursor. In the presence of strong ligands like tri-n-octylphosphine, the particle yield is reduced and no CdS forms, when alcohol is replaced by typical coordinating solvents, such as tri-n-octylphosphine oxide and hexadecylamine. This implies that under the given conditions, solvents with a stronger coordination power than alcohol inhibit the precursor conversion into monomers. Furthermore, the particle growth in alcohol is widely independent from the initial precursor concentration, indicating that our synthesis follows the LaMer model. Finally, a 1H NMR study and control experiments with different alcohols and non-coordinating solvents prove that fatty alcohols are good surface ligands for CdS quantum dots. Our results demonstrate that the sulfur reactivity or the cleavage of the PS bond in tri-n-alkylphosphine sulfide is not the bottleneck in the synthesis of CdS quantum dots, if a solvent with an appropriate coordination power is used.