Solution processable visible-light and color-selective image sensor with a ZnO/QDs/ZrO2 sandwich structure

Abstract

Quantum dots (QDs) are emerging materials for optoelectronic devices because of their facile tunable bandgap and solution processability. However, overcoming inherent problems, such as vulnerability to atmospheric moisture and the persistence photoconductivity (PPC) effect originating from trap states, is necessary. We proposed a method to enhance the stability and reduce the PPC effect by adding a ZrO2 passivation layer above the QDs layer. The ZrO2 layer effectively reduced the trap state of the QDs, passivated the QDs from external environmental oxygen and moisture, and simultaneously acted as an additional channel. Interfacial analyses were conducted using X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), time-resolved photoluminescence (TRPL), and high-resolution transmission electron microscopy (HR-TEM) measurements. Hence, the device showed enhanced photoresponsivity and photosensitivity of 2.6 × 103 A/W and 6.67 × 105, respectively. Additionally, the device showed a highly reduced PPC effect with a rate of current increase of 0.017 under periodic 635 nm wavelength light illumination. Moreover, it showed reliable long-term stability over 30 days under a relative humidity of ∼40%. Therefore, a color-selective image sensor was successfully demonstrated, and the device could recognize red/green/blue colors owing to its reduced PPC effect and high stability. Our results suggest a useful method for developing next-generation QD-based transparent optoelectronic devices.