Multi-stacked hybrid graphene and quantum dot films for high response photodetection

University Of California-San Diego, La Jolla CA

Investigators

Abstract

Title: Hybrid graphene and quantum dot films for high response photodetection Abstract Non-technical: Conversion of light to electricity is at the core of photodetection and photovoltaic devices that are critical for cameras, fast communications, information processing, biodetection, biomedical instruments, and energy harvesting. One of the main challenges for light detection is developing new technologies with low power consumption that can be thin and flexible to facilitate its use on wearable and portable devices. This project aims to develop a hybrid and ultrathin technology combining the strong light absorption of semiconducting nanoparticles (quantum dots) with the high electrical conductivity of one-atom thick carbon layers (graphene). The strategy for this project is to use quantum dots to collect light and generate electrical charges that will be collected by intercalated graphene layers for efficient charge transport. The intercalated graphene layers will serve as an efficient network of highly conductive paths for electrical charges inside the photodetector. Combining these nanomaterials would allow ultrathin photodetectors with high sensitivity and low power consumption that can be implemented on flexible and wearable devices. This project will also set a platform to train a new generation of students and engineers on the properties and applications of nanomaterials for optoelectronics and sunlight energy harvesting applications. Furthermore, this project will also help to disseminate new advances in nanotechnology for underrepresented communities, especially in high-schools in Hispanic communities in the region of Southern California. Technical: The goal for this project is to develop lead-sulfide quantum dot photodetectors with enhanced photoresponse using intercalated graphene layers for efficient current collection. It is a well-known restriction that for efficient current extraction with conventional top/bottom contacts, the thickness of the absorbing layers should not exceed the carrier diffusion length. If the films are thicker, then the photocarriers recombine before being collected by the top/bottom electrodes. This project aims to overcome this restriction by using intercalated layers with spacing shorter than the carrier diffusion length, allowing the efficient collection of photocharges before they recombine. This is an innovative strategy to break the limitation that diffusion length imposes on light absorbing layers and therefore boost the performance of optoelectronic devices. The first goal of the project will be to study the charge transfer dynamics and photoresponse at a graphene/quantum dot interface. Both materials have been largely studied, but their joint hybrid heterojunction is still largely unexplored. Since both are quantum confined systems with strong surface dependent behavior, the charge transfer can substantially differ from normal 'bulk' junctions. The technology to build the intercalated quantum dots and graphene devices will be developed based on low-temperature processing compatible with both nanomaterials, such as spin coating of quantum dots and graphene transfer. Integrating different nanomaterials in a single device can open a new route to develop high performing nanoscale devices combining their properties. Our analysis of the devices will be based on light absorption, photoresponsivity, and quantum efficiency measurements. The measurements will focus on studying the performance enhancement as function of the thickness of the absorbing layer and the spacing between graphene layers. This project has the potential to develop a new architecture for optoelectronic devices with superior carrier collection efficiency.