Size-dependent charge collection in junctions containing single-size and multi-size arrays of colloidal CdSe quantum dots.

This paper describes the electrical characteristics of junctions composed of three-dimensional arrays of colloidal CdSe quantum dots (QDs) with tin-doped indium oxide (ITO)/poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS) and eutectic Ga-In (EGaIn) electrodes. It focuses on a comparison of junctions containing QDs of one size to those of arrays containing QDs of multiple sizes. This comparison makes it possible to estimate the relative contributions of transport across various interfaces (e.g., between the QDs and between the QDs and the electrodes) to the observed electrical characteristics of the junction and to evaluate the dependence of these contributions on the locations of various sizes of QDs within the junction. The junctions were diodes, and their turn-on voltage depended on the size of the QDs next to the PEDOT:PSS. We describe this dependence using a Marcus model to estimate the barrier for charge transfer induced by the difference in energies between the orbitals of the QDs and the valence band of PEDOT:PSS.

The use of size-selective excitation to study photocurrent through junctions containing single-size and multi-size arrays of colloidal CdSe quantum dots.

This paper describes a study of the generation and flow of photocurrent through junctions containing three-dimensional arrays of colloidal CdSe quantum dots (QDs) of either a single size or multiple sizes. The electrodes were indium tin oxide (ITO) covered with a thin layer of poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS) and a eutectic alloy of Ga and In (EGaIn). We measured the current-voltage characteristics of the junctions in the dark and under illumination, with various sources and wavelengths of excitation, and their photocurrent action spectra. Size-selective photoexcitation of the arrays of multiple sizes of QDs helped to determine (i) the location of the interface at which photoinduced separation of charge occurred, (ii) whether the energy absorbed by the QDs was redistributed before separation of charge, and (iii) the dependence of the photovoltage on the locations of various sizes of QDs within the junction. This research is a step toward the use of QDs for harvesting light and for transporting energy and charge in devices-for example, solar cells and photodetectors-that operate at zero bias.

Synthesis of CdSe/CdTe nanobarbells.

Synthesis of monodisperse samples of CdSe nanorods with CdTe tips is achieved using the mechanism of rod nucleated growth to form CdSe/CdTe nanobarbells. This synthesis produces a nanocrystal displaying "type-II" behavior with a morphology that is particularly well suited for internal exciton separation and carrier transport.