Self-Assembled Structures of Semiconductor Nanocrystals and Polymers for Photovoltaics. 1. CdSe Nanocrystal−Polymer Multilayers. Optical, Electrochemical, Photoelectrochemical and Photoconductive Properties

Abstract

Hybrid materials of polymers and cadmium selenide nanocrystals (CdSe-NCs) were produced through a layer-by-layer deposition technique. Polymer series comprises sulfonic, phosphonic, and carboxylic acids; pyridine- and amine-based polymers; and some related bipolar amphiphiles, including a dithiol. Nonaqueous dispersions of amine- and oleate-capped CdSe-NCs with 3, 4, and 5 nm diameters were used. Polymers and CdSe-NCs are alternately deposited on indium-tin-oxide/glass surfaces. CdSe-NCs layers undergo a sharp and irreversible electroxidation process in acetonitrile corresponding to the passage of two electrons per CdSe unit. The multilayer build-up, monitored by UV−vis spectroscopy and cyclic voltammetry, shows an increase in the film absorbance and oxidation stripping charge proportional with the number of adsorbed CdSe layers and with the particle diameter. Layer formation rate by acids follows their acidity, with thiols being much slower than sulfonic, phosphonic, or carboxylic acids. The semiconductor properties of the multilayers were evidenced by photoluminescence (PL), photoelectrolchemical, and photoconduction analysis. Good PL was recorded in pyridine-, amine-, and carboxylate-based multilayers, PL quenching in sulfonate-, phosphonate-, and thiolate-based multilayers. PL quenching is accompanied by higher photoelectrochemical and photoconductivity responses.

Electrochemical Characterization of CdSe Monolayers Modified with Glycosilated Molecules

“…The oxidative charge obtained by the integration of the 1.2 V peak is ca 0.9 mC cm À2 and, compared to the CdSe coverage estimated by UV-vis determinations (Figure SI03), corresponds to the passage of two electrons per CdSe unit, i. e. to the total demolition of the CdSe-NCs forming the monolayer, like the previously reported oxidation process in organic medium [11]. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 The electrochemical responses of these glycosilated electrodes were investigated after their incubartion in Jacalin solutions.…”

“…As shown in Figure , these films with external sugar‐molecules have been characterized in aqueous electrolyte (pbs+0.1 M NaCl) and have revealed an irreversible oxidation process at 1.2 V, like the one observed in the previously reported organic medium . This process occurs at a much lower potenetial value than the one of the same films with the native ligands HDA and SA, which is an irreversible shoulder at 1.7 V, Figure .…”

“…The oxidative charge obtained by the integration of the 1.2 V peak is ca 0.9 mC cm −2 and, compared to the CdSe coverage estimated by UV‐vis determinations (Figure SI03), corresponds to the passage of two electrons per CdSe unit, i. e. to the total demolition of the CdSe‐NCs forming the monolayer, like the previously reported oxidation process in organic medium .…”

“…Soluble CdSe‐NCs with the surface capped by hexadecylamine (HDA) and stearic acid (SA) were produced as previously reported . The NCs display absorption maximum at 620 nm (Figure SI01) corresponding to an average size of 5.6 nm .…”

Emulsion-directed liquid/liquid interfacial fabrication of lanthanide ion-doped block copolymer composite thin films

“…However, homogeneous dispersal of functional species, such as metal ions, metal complexes, small molecules, and inorganic nanoparticles, in polymer matrices remains a great challenge. In order to incorporate these species into polymer matrices, various methods have been proposed and developed [3], such as mixing [4], layer-by-layer assembly [5], electrospinning [6], template-induced polymerization [7], and self-assembly [8].…”