Proceedings of nanoGe Fall Meeting 2018 (NFM18)
Publication date: 6th July 2018
Colloidal semiconductor quantum dots are attractive materials for realizing solution processable lasers[1]. However, light amplification and optical gain in these materials is relatively hard to achieve, due to the non-unity degeneracy of the electron and hole states, which implies that multiexcitons are necessary to reach the lasing regime[2]. A better understanding of the relationship between carrier population and optical gain will give solid handholds to improve these materials for applications in low-threshold gain media.
Here, we present a model which is able to describe the build-up of optical gain in semiconductor quantum dots, and we validate the model with femto-second transient absorption spectroscopy (fs-TA). We perform fluence-dependent fs-TA measurements on CdSe/CdS/ZnS nanocrystals, which serves as a well-established platform test the feasibility of our model. The model itself is build up out of three parts: (1) a transition-counting scheme, which explicitly considers the relative weights of the electron and hole contributions to the band-edge absorption bleach, also when the number of excitons exceeds the degeneracy of the band edge states, (2) Poissonian excitation statistics, and (3) a coupled differential equation scheme which takes into account Auger recombination during the cooling of hot carriers. The only experimental inputs are the absorption cross-section of the quantum dots (to obtain the average exciton occupancy per nanocrystal) and the biexciton lifetime, which both are readily recovered from the fs-TA measurements. The experimental data is accurately reproduced with our model, which demonstrates the feasibility of the model.
The unique approach of modelling combined with quantitative fs-TA allows us to create a complete description of the build-up of optical gain in quantum dot materials. Furthermore, the presented model can also be used to determine the band-edge degeneracies for less well-established quantum dot systems (e.g. InP and CuInS). The experiments presented here open up pathways for more quantitative studies of optical gain in semiconductor quantum dots and help rationalize design rules for novel low threshold gain materials.
AJH, JJG and WvdS gratefully acknowledge financial support from the European Research Council Horizon 2020 ERC Grant Agreement No. 678004 (Doping on Demand). GG acknowledges financial support from STW (Project No. 13903, Stable and Non-Toxic Nanocrystal Solar Cells).
nanoGe is a prestigious brand of successful science conferences that are developed along the year in different areas of the world since 2009. Our worldwide conferences cover cutting-edge materials topics like perovskite solar cells, photovoltaics, optoelectronics, solar fuel conversion, surface science, catalysis and two-dimensional materials, among many others.
Previously nanoGe Spring Meeting (NSM) and nanoGe Fall Meeting (NFM), MATSUS is a multiple symposia conference focused on a broad set of topics of advanced materials preparation, their fundamental properties, and their applications, in fields such as renewable energy, photovoltaics, lighting, semiconductor quantum dots, 2-D materials synthesis, charge carriers dynamics, microscopy and spectroscopy semiconductors fundamentals, etc.
International Conference on Hybrid and Organic Photovoltaics
International Conference on Hybrid and Organic Photovoltaics (HOPV) is celebrated yearly in May. The main topics are the development, function and modeling of materials and devices for hybrid and organic solar cells. The field is now dominated by perovskite solar cells but also other hybrid technologies, as organic solar cells, quantum dot solar cells, and dye-sensitized solar cells and their integration into devices for photoelectrochemical solar fuel production.
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
The main topics of the Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics (IPEROP) are discussed every year in Asia-Pacific for gathering the recent advances in the fields of material preparation, modeling and fabrication of perovskite and hybrid and organic materials. Photovoltaic devices are analyzed from fundamental physics and materials properties to a broad set of applications. The conference also covers the developments of perovskite optoelectronics, including light-emitting diodes, lasers, optical devices, nanophotonics, nonlinear optical properties, colloidal nanostructures, photophysics and light-matter coupling.
The International Conference on Perovskite Thin Film Photovoltaics Perovskite Photonics and Optoelectronics (NIPHO) is the best place to hear the latest developments in perovskite solar cells as well as on recent advances in the fields of perovskite light-emitting diodes, lasers, optical devices, nanophotonics, nonlinear optical properties, colloidal nanostructures, photophysics and light-matter coupling.