Exploring the Limits for High-performance LEDs and Solar Cells

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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 Förster transfer that can compete with the intrinsic recombination of the excitations," Itskos explained. Förster 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 Förster. 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 Förster resonant energy transfer.

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