Lateral heterojunction photodetector consisting of molecular organic and colloidal quantum dot thin films

Abstract

We demonstrate a heterojunction photodetector of lateral geometry that utilizes an evaporated film of the hole-transporting molecular material N , NЈ-bis͑3-methylphenyl͒-N , NЈ-bis͑phenyl͒-9,9-spirobifluorene ͑spiro-TPD͒ as a charge transport layer and that is sensitized across visible wavelengths by a thin film of colloidal CdSe nanocrystal quantum dots ͑QDs͒. High photon-to-electron quantum conversion efficiencies are obtained at room temperature as a result of photoconductive gain. With an electric field of 3.0ϫ 10 5 V / cm applied across the electrodes, we measure the external quantum efficiency at the first QD absorption peak ͑at wavelength = 590 nm͒ to be 13%, corresponding to an internal quantum efficiency of approximately 80%. The operating mechanism of these devices is discussed, noting that the optical response is dominated by the QD absorption spectrum while the charge transport nearly exclusively takes place in the spiro-TPD.

Long‐Range Visible Fluorescence Tunability Using Component‐Modulated Coupled Quantum Dots

“…[ 21 ] The promise of in-plane conformation variation is of practical importance because a fi xed biasing across a close-packed monolayer of asymmetric coupled dots may provide a route to control electronic properties for different conformations that may lead in realizing the q-bits for quantum information processing, [ 22 , 23 ] in addition to application in optoelectronic devices. [24][25][26] In principle, control over coupled junction provides a means for controlling quantum coupling interactions, the extent of which can be controlled by tuning synthetic conditions. The intermixing between constituent nanomaterials may result in new intermediate transition states depending on the size of the constituents, which could be useful in tailoring long-range emissions in the visible or IR range.…”

A tunable colloidal quantum dot photo field-effect transistor

“…Most photodetectors function either as photodiodes or as photoconductors: photodiodes offer fast response and low dark current, while photoconductors provide built-in gain associated with the use of long-lived sensitizing centers. The concept of a phototransistor, such as a photo-field-effecttransistor (photoFET), 1 offers an attractive possibility: gain united with a lowered dark current compared to the photoconductor, achieved if the thickness of the current-carrying channel can be chosen independently from the thickness of the light-absorbing layer.…”

Colloidal quantum dot photodetectors

“…2 and Refs. [20,23,25,26,28,47,48].). These traps serve both to delay band-to-band recombination, and also to impede the extraction of the trapped carrier, a condition necessary to photoconductive gain.…”