Medical University of South Carolina

Massachusetts Institute of Technology

Andrew B Greytak

Mathew Kelley

Mvs Chandrashekhar

Joshua Letton

Moungi G Bawendi

Wenhao Liu

Daniel G Nocera

Peter Matthew Allen

M V S Chandrashekhar

Yi Shen

Spatially resolved Fourier Transform Impedance Spectroscopy (FTIS) is disclosed to spatially map and quickly build the frequency response of optoelectronic devices using optical probes. The transfer function of a linear system is the Fourier transform of its impulse response, which may be obtained from transient photocurrent measurements of devices such as photodetectors and solar cells. We apply FTIS to a PbS colloidal quantum dot (QD)/SiC heterojunction photodiode and corroborate results using intensity-modulated photocurrent spectroscopy. The cutoff frequencies of the QD/SiC devices were as high as ˜10 kHz, demonstrating their utility in advanced flexible and thin film electronics. The practical frequencies for FTIS lie in the mHz-kHz range, ideal for composite or novel materials such as QD films that are dominated by interfacial trap states.

Spatially resolved fourier transform impedance spectroscopy and applications to optoelectronics

The present disclosure is directed to methods for producing a photovoltaic junction that can include coating a bare junction with a composition. In one embodiment, the composition includes a plurality of quantum dots to create a film; exposing the film to a ligand to create a first layer; coating the first layer with the composition to form a film on the first layer; and exposing the film on the first layer to the ligand to create a second layer.

Methods of producing a photovoltaic junction including ligand exchange of quantum dots of a film

The present disclosure is directed to photovoltaic junctions and methods for producing the same. Embodiments of the disclosure may be incorporated in various devices for applications such as solar cells and light detectors and may demonstrate advantages compared to standard materials used for photovoltaic junctions such as silica. An example embodiment of the disclosure includes a photovoltaic junction, the junction including a light absorbing material, an electron acceptor for shuttling electrons, and a metallic contact. In general, embodiments of the disclosure as disclosed herein include photovoltaic junctions which provide absorption across one or more wavelengths in the range from about 200 nm to about 1000 nm, or from near IR (NIR) to ultra-violet (UV). Generally, these embodiments include a multi-layered light absorbing material that can be formed from quantum dots that are successively deposited on the surface of an electron acceptor (e.g., a semiconductor).

Quantum dot photovoltaic junctions

A semiconductor nanocrystal can have a photoluminescent quantum yield of at least 90%, at least 95%, or at least 98%. The nanocrystal can be made by sequentially contacting a nanocrystal core with an M-containing compound and an X donor, where at least one of the M-containing compound and the X donor is substoichiometric with respect to forming a monolayer on the nanocrystal core.

Highly luminescent semiconductor nanocrystals

Methods for purifying nanocrystals via gel permeation chromatography are provided. The method can include: loading a sample solution into a chromatography column, wherein the sample solution comprises nanocrystals coated with a layer of organic ligands; using an eluent, passing the nanocrystals coated with the layer of organic ligands through a stationary phase of the chromatography column, wherein the eluent is an organic solvent in which the nanocrystals coated with the layer of organic ligands remain miscible to form a mobile phase; and collecting the mobile phase passed through the stationary phase of the chromatography column. The surface ligands of the purified nanocrystals can then be, in one embodiment, replaced with a second type of ligand.

Growing community of inventors

Columbia, SC, United States of America

Andrew B Greytak