Periodic Reporting for period 1 - PEROGAN (Novel Light Emitters based on Nanostructures of III-Nitrides and Lead Halide Perovskite Nanocrystals)
Berichtszeitraum: 2020-01-01 bis 2021-12-31
Recent advancements in semiconductor science and technology have enabled the development of niche commercial optoelectronic applications such as lasers, energy efficient light emitting diodes for lighting and displays. For the generation of white light emission, the current technology is based in two approaches. Currently commercially available white light is generated via the down-conversion of blue photons arising from an InGaN light emitting diodes (LED) to yellow/green-red light phosphor materials. Such approach lack of performance as it is still well below their potential luminous efficacy of up to 350 lm/W, with the down-conversion efficiency, color purity and operational frequency limited by the phosphor self-absorption losses, broad emission, and microsecond-long radiative lifetimes. On the second method, the integration of red, green, and blue LEDs (RGB) in one module produces white light based on proper mixture of the red, green, and blue emission. Blue and red electroluminescence in such schemes can be produced by high performance InGaN- and GaInP-based LEDs respectively, however efficient green emission remains challenging, while the integration of these devices on the same chip is a complex task to do. Recently a new class of materials known as lead halide perovskite nanocrystals (LHP NCs), have emerged as exceptional emitters with high luminescence efficiency, exceeding 90% in the green spectral region combined with narrow emission linewidths and tunability across the visible via facile ion exchange reactions. The characteristics of such nanomaterials renders them highly promising for optoelectronic and photonic applications.
The present project aims to develop, new and efficient hybrid emitter system based on the integration of III-nitride LEDs and LHP NCs, allowing them to exploit the strengths and potentials of both material families. The proposed work focuses on the study and optimization of the down-conversion of nitride emission involving the NCs using two approaches: (i) via radiative pumping in which UV/blue photons emitted from InGaN LEDs are absorbed by the LHP NCs and converted efficiently to longer wavelength photons, (ii) via Förster resonant energy transfer (FRET) in which energy channelling occurs non-radiatively via dipole-dipole coupling. The latter approach could overcome intrinsic limitations of the radiative pumping process which is relatively inefficient and slow. Eventually the synergy of processes (i) and (ii) will be sought to mediate the light emission process in the novel light emitting structures of the project.The development of novel and efficient white light LEDs, apart from the explicit applications in solid state lighting, will benefit several other commercial sectors such as displays, data communications, machine vision and biomedicine. For display applications, down-conversion via LHP NCs offers high colour saturation and purity due to their narrow emission linewidths. Visible light communication (LiFi) is expected to grow rapidly to meet the increasing demand of data transmission speed and bandwidths over the last years; the combination of nitrides with LHP NCs appears highly suitable for such applications, as they both exhibit fast radiative rates, allowing in principle such hybrid devices to operate at high modulation frequencies necessary for high data transmission rates. The aforementioned outcomes would greatly affect the wider society and public, as it is expected to have a great impact on the quality of life and economic growth in the future. The initial project objective is the study and optimization of the radiative- and non-radiative light down-conversion from an optically-pumped blue emitting LED based on InGaN/GaN multiple quantum wells (MQWs) to green/red absorbing LHP NC layers. In order to activate FRET, the use of nanostructured InGaN structures will be sought to allow a close proximity of nitride and NC excitations that can be coupled via the strong dipole-dipole interaction. The second objective of the project will be to develop the idea in order to demonstrate multicolor and white light emission via non-radiative and/or radiative pumping of LHP NCs from electrically excited, nanostructured InGaN-based LEDs. Finally, the project aims to investigate optically pumped LHP NCs for lasing applications, via electrical excitation of InGaN/GaN LEDs by employing a more elaborate structure design of a double-microcavity arrangement.
The present project aims to develop, new and efficient hybrid emitter system based on the integration of III-nitride LEDs and LHP NCs, allowing them to exploit the strengths and potentials of both material families. The proposed work focuses on the study and optimization of the down-conversion of nitride emission involving the NCs using two approaches: (i) via radiative pumping in which UV/blue photons emitted from InGaN LEDs are absorbed by the LHP NCs and converted efficiently to longer wavelength photons, (ii) via Förster resonant energy transfer (FRET) in which energy channelling occurs non-radiatively via dipole-dipole coupling. The latter approach could overcome intrinsic limitations of the radiative pumping process which is relatively inefficient and slow. Eventually the synergy of processes (i) and (ii) will be sought to mediate the light emission process in the novel light emitting structures of the project.The development of novel and efficient white light LEDs, apart from the explicit applications in solid state lighting, will benefit several other commercial sectors such as displays, data communications, machine vision and biomedicine. For display applications, down-conversion via LHP NCs offers high colour saturation and purity due to their narrow emission linewidths. Visible light communication (LiFi) is expected to grow rapidly to meet the increasing demand of data transmission speed and bandwidths over the last years; the combination of nitrides with LHP NCs appears highly suitable for such applications, as they both exhibit fast radiative rates, allowing in principle such hybrid devices to operate at high modulation frequencies necessary for high data transmission rates. The aforementioned outcomes would greatly affect the wider society and public, as it is expected to have a great impact on the quality of life and economic growth in the future. The initial project objective is the study and optimization of the radiative- and non-radiative light down-conversion from an optically-pumped blue emitting LED based on InGaN/GaN multiple quantum wells (MQWs) to green/red absorbing LHP NC layers. In order to activate FRET, the use of nanostructured InGaN structures will be sought to allow a close proximity of nitride and NC excitations that can be coupled via the strong dipole-dipole interaction. The second objective of the project will be to develop the idea in order to demonstrate multicolor and white light emission via non-radiative and/or radiative pumping of LHP NCs from electrically excited, nanostructured InGaN-based LEDs. Finally, the project aims to investigate optically pumped LHP NCs for lasing applications, via electrical excitation of InGaN/GaN LEDs by employing a more elaborate structure design of a double-microcavity arrangement.
Significant progress has been made within the project activities, in terms of demonstrating efficient light down-conversion from InGaN MQW-based nanostructures via LHP NCs. The nitride nanostructures implemented in this initial stage, are in the form of nanohole photonic structures that are overcoated by three types of LHP NCs, namely green-emitting CsPbBr3, green-emitting FAPbBr3 and near-IR emitting FAPbI3 NCs. Such hybrid structures allow for a close proximity of nitride and NC excitations and are found to support highly efficient non-radiative energy transfer from the nitride MQW donors to the NC acceptors of energy. Evidence of such transfer process is provided by investigating the emission characteristics i.e. intensity and dynamics of the donor (InGaN MQW) and acceptor (LHP NCs) materials in both the steady state and transient regime. In particular the optical experiments indicate the presence of FRET with efficiencies higher than 70% that occurs at relatively fast timescales of 5 to 10 ns with a Forster radius in the range of 4-5 nm. The summary of the aforementioned results is reported in a publication in ACS Applied Nanomaterials Journal. Hybrid InGaN white light devices with LHP NCs as down converting media were demonstrated under electrical excitation, yielding in emission with high color rendering index (CRI) approaching 90, CIE coordinates of 0.33,0.38 approaching pure white light white (CIE of 0.33,0.33) and a cool-white color temperature of 5500K. In addition, all-solution process microcavities were demonstrated with ability to sustain efficient amplified spontaneous under continuous wave excitation, with threshold down to 140mW/cm2. The summary of the aforementioned results is reported in a publication in ACS Photonics Journal. As final remark, multi-color ASE from free standing, flexible microcavities was demonstrated, with the ability to sustain ASE simultaneously in the green and red part of the spectrum region.
Promising results during the duration of the project in terms of the performance for such hybrid devices.For the first time efficient FRET has been reported between the two material families of III-Nitrides and LHP NCs. The present results demonstrate efficiencies greater than 70%, which are close or higher to other hybrid systems previously reported.A prototype efficient hybrid system with multicolour/white emission under electrical excitation was demonstrated, paving the way towards the development of next generation white light sources with enhanced optical performance. In addition, efficient amplified spontaneous emission, from solution process micro resonators under CW excitation was demonstrated , opening the horizons towards the realization of low-cost solution process lasers.It is believed that results will have a high impact in the scientific community and industry devoted to displays, high CRI LEDs for solid state lighting, visible light communications, biomedical applications and laser applications.