Subscribe to our free daily newsletters
  Solar Energy News  

Subscribe to our free daily newsletters

Exploring the limits for high-performance LEDs and solar cells
by Staff Writers
London, UK (SPX) Dec 09, 2015

In the top left is a schematic of Forster Resonant Energy Transfer from a near-surface nitride quantum well to a polymer overlayer. In the top right is fluorescence from solutions containing light emitting polymer materials. In the bottom left high resolution transmission electron microscope image from an InGaN/GaN quantum well. In the bottom right absorption and fluorescence spectra from various polymers used in our study. Image courtesy Grigorios Itskos/University of Cyprus, Cyprus. For a larger version of this image please go here.

Hybrid optoelectronic devices based on blends of hard and soft semiconductors can combine the properties of the two material types, opening the possibility for devices with novel functionality and properties, such as cheap and scalable solution-based processing methods. However, the efficiency of such devices is limited by the relatively slow electronic communication between the material components that relies on charge transfer, which is susceptible to losses occurring at the hybrid interface.

A phenomenon called Forster resonant energy transfer (FRET) was recently theoretically predicted and experimentally observed in hybrid structures combining an inorganic quantum well with a soft semiconductor film.

Forster resonant energy transfer is a radiationless transmission of energy that occurs on the nanometer scale from a donor molecule to an acceptor molecule. The process promotes energy rather than charge transfer, providing an alternative contactless pathway that avoids some of the losses caused by charge recombination at the interface.

Now researchers from the University of Cyprus and Cyprus University of Technology, along with colleagues from the University of Crete, Greece have conducted a comprehensive investigation on how various structural and electronic parameters affect FRET in structures of nitride quantum wells with light-emitting polymers.

Based on their studies, the researchers discuss the process to optimize the energy transfer process and identify the limitations and implications of the Forster mechanism in practical devices. The work demonstrates the importance of understanding FRET in hybrid structures that could pave the way for developing novel devices such as high-efficiency LEDs and solar cells. The researchers present their work in a paper published this week in the Journal of Chemical Physics, from AIP Publishing.

"Pioneering theoretical and experimental work has demonstrated that energy can be efficiently transferred across hybrid semiconductors via the Forster mechanism. However, our understanding is not complete and many material and structural parameters affecting FRET in such hybrids remain unexplored.

Our work employs for a first time a comprehensive approach that combines fabrication, theoretical modeling and optical spectroscopy to fully understand FRET in a nitride quantum well-polymer hybrid structure," said Grigorios Itskos, the primary researcher and an assistant professor from the Department of Physics at the University of Cyprus.

"We used a systematic approach to optimize the FRET efficiency by tuning various parameters of the nitride quantum well component. The process allowed us to study unexplored aspects of the mechanism and identify competing mechanisms that limit the energy transfer efficiency in hybrid planar structures.

"The outcome of our investigation can guide future efforts towards a rational design of hybrid geometries that can optimize FRET and limit competing losses to render FRET-based devices feasible," he said.

Itskos noted that the researchers chose to study structures based on nitrides because the material is well-researched and is used in niche applications such as blue light emitting LEDs.

"However, the functionality [of nitride structures] can be further increased by combining them with other soft semiconductors such as light-emitting polymers. The spectral tunability and high light-absorption and emitting efficiency of the polymers can be exploited to demonstrate efficient down-conversion of the blue nitride emission, providing a scheme for efficient hybrid LEDs," Itskos said.

In the study, the researchers initially sought to produce and study near-surface nitride quantum wells to allow a close proximity with the light-emitting polymer deposited on their top surface.

"The nanoscale proximity promotes efficient interactions between the excitations of the two materials, leading to fast Forster transfer that can compete with the intrinsic recombination of the excitations," Itskos explained.

Forster resonant energy transfer is a strongly distance-dependent process which occurs over a scale of typically 1 to 10 nanometers. The contactless pathway of energy transmission could avoid energy losses associated with charge recombination and transport in hybrid structures.

Using a sequence of growth runs, theoretical modeling and luminescence spectroscopy (a spectrally-resolved technique measuring the light emission of an object), the researchers identified the way to optimize the surface quantum well emission.

"We studied the influence of parameters such as growth temperature, material composition, and thickness of the quantum well and barrier on the optoelectronic properties of the nitride structures. Increase of the quantum confinement by reducing the width or increasing the barrier of the quantum well increases the well emission.

However, for high quantum well confinement, excitations leak to the structure surface, quenching the luminescence. So there is an optimum set of quantum well parameters that produce emissive structures," Itskos said.

He also pointed out that the studies indicate a strong link between the luminescence efficiency of the nitride quantum well with the FRET efficiency of the hybrid structure, as predicted by the basic theory of Forster. The correlation could potentially provide an initial and simple FRET optimization method by optimizing the luminescent efficiency of the energy donor in the absence of the energy acceptor material.

"Our studies also indicated that electronic doping of the interlayer between the nitride quantum well and the polymer film reduces the efficiency of FRET. This constitutes a potential limitation for the implementation of such hybrid structures in real-world electronic devices, as electronic doping is required to produce efficient practical devices. Further studies are needed to establish the exact influence of doping on FRET," Itskos noted.

He said the team's next step is to perform a systematic study of hybrid structures based on doped nitride quantum wells to investigate the mechanisms via which electronic doping affects the characteristics of the Forster resonant energy transfer.

The article, "Forster resonant energy transfer from an inorganic quantum well to a molecular material: Unexplored aspects, losses and implications to applications," is authored by Grigorios Itskos, Andreas Othonos, Stelios A. Choulis and Eleftherios Iliopoulos. It was published in the Journal of Chemical Physics on Dec. 1, 2015 (DOI: 10.1063/1.4935963) and can be accessed here.

Thanks for being here;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.

SpaceDaily Contributor
$5 Billed Once

credit card or paypal
SpaceDaily Monthly Supporter
$5 Billed Monthly

paypal only


Related Links
American Institute of Physics
All About Solar Energy at

Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks DiggDigg RedditReddit GoogleGoogle

Previous Report
Google to boost renewable energy for data centers
Washington (AFP) Dec 3, 2015
Google announced plans Thursday to boost its use of renewable energy for its data centers, moving closer to its goal of 100 percent clean energy use. The US tech giant said it signed agreements to boost its use of wind and solar energy by contracting to buy 842 megawatts of electricity. The deals include purchases of solar energy from the United States and Chile, and wind power from Swed ... read more

OX2 wins concession for one of Sweden's largest biogas plants

Brazil pins renewable energy hopes on 2nd generation ethanol

A more efficient way of converting ethanol to a better alternative fuel

Now is the time to uncover the secrets of the Earth's microbiomes

UW roboticists learn to teach robots from babies

Kennedy now firmly established as a 21st Century Spaceport

These are the robots you're looking for

Japan shows off disaster-response robots at android fair

Pilot Hill Wind Project Closes Financing from GE and MetLife

German power giant RWE to spin off renewables business

Big UK cities vow to run on green energy by 2050

SeaPlanner New Features Launched on Nordsee One Offshore Wind Farm

GM to sell China-made vehicle in US first

Eliminating 'springback' to help make environmentally friendly cars

Lyft allies with Asia peers in Uber challenge

VW needs to be more modest, new CEO says

Scientists see the light on microsupercapacitors

Storing electricity in paper

Saft to supply LION batteries to power Textron control stations

36 countries launch world alliance for geothermal energy

Nuclear power as panacea for climate change? Experts divided

Ship carrying nuclear waste arrives in Australia

Hungary open to dialogue with EU over nuclear plant expansion

Nuclear power crucial for UN climate goal: top scientist

Addressing climate change should start with energy efficiency

CO2 emissions set for historic fall in 2015: study

Banks move to support sustainable transport sector

China vows massive clean-up of power plants: Xinhua

'Traditional authority' linked to rates of deforestation in Africa

Forest Service scientists improve US forest carbon accounting

UF creates trees with enhanced resistance to greening

Tallest trees could die of thirst in rainforest droughts

Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News

The content herein, unless otherwise known to be public domain, are Copyright 1995-2017 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement