High Efficiency Colloidal Quantum Dot Infrared Light Emitting Diodes via Engineering at the Supra-Nanocrystalline Level

Colloidal quantum dot (CQD) light-emitting diodes (LEDs) deliver a compelling performance in the visible, yet infrared CQD LEDs underperform their visible-emitting counterparts, largely due to their low photoluminescence quantum efficiency. Here we employ a ternary blend of CQD thin film that comprises a binary host matrix that serves to electronically passivate as well as to cater for an efficient and balanced carrier supply to the emitting quantum dot species. In doing so, we report infrared PbS CQD LEDs with an external quantum efficiency of ~7.9% and a power conversion efficiency of ~9.3%, thanks to their very low density of trap states, on the order of 1014 cm−3, and very high photoluminescence quantum efficiency in electrically conductive quantum dot solids of more than 60%. When these blend devices operate as solar cells they deliver an open circuit voltage that approaches their radiative limit thanks to the synergistic effect of the reduced trap-state density and the density of state modification in the nanocomposite.Peer ReviewedPostprint (author's final draft

Comparison of SC fibers for fs Ti:Sapphire based hyperspectral CARS microscopy

Hyperspectral coherent anti-Stokes Raman scattering (CARS) microscopy is a rapidly developing field enabling label-free, chemically selective bio-imaging based on Raman signatures [1]. A significant factor limiting its clinical application is the complexity of current laser sources. A solution immediately relevant to two-photon excited fluorescence imaging laboratories is coherently broadening a fs Ti :Sapphire laser seed in a fiber to provide the Raman wavelengths via spectral-focusing (SF) CARS. The NKT fiber with two Zero Dispersion Wavelengths (ZDWs) is one option but the spectrum exhibits low Power Spectral Density (PSD) because of the large (&gt;800 nm) spectral broadening. Here we perform the first systematic comparison sweeping (i) input pump power, (ii) pump wavelength and (iii) fiber length comparing the coherent SC from a femtoWHITE-CARS (2 ZDWs) fiber, a fiber with one ZDW offset above the seed wavelength, and an all-normal dispersion (ANDi) fiber. Starting with the seed laser polarisation aligned to a principal fiber axis, we show the total experimentally measured spectral output and importantly the polarisation resolved spectral component on the orthogonal axis, which is a measure of the nonlinear power-dependent depolarisation[2]. This orthogonal component will degrade the efficiency of the CARS signal but still contributes to the bio-toxicity that limits the maximum power for imaging. Finally, we show representative SF-CARS microscopy images to showcase the power of this technique.</p

Highly efficient quantum dot near-infrared light-emitting diodes

Colloidal quantum dots (CQDs) are emerging as promising materials for constructing infrared sources in view of their tunable luminescence, high quantum efficiency and compatibility with solution processing1. However, CQD films available today suffer from a compromise between luminescence efficiency and charge transport, and this leads to unacceptably high power consumption. Here, we overcome this issue by embedding CQDs in a high-mobility hybrid perovskite matrix. The new composite enhances radiative recombination in the dots by preventing transport-assisted trapping losses; yet does so without increasing the turn-on voltage. Through compositional engineering of the mixed halide matrix, we achieve a record electroluminescence power conversion efficiency of 4.9%. This surpasses the performance of previously reported CQD near-infrared devices two-fold, indicating great potential for this hybrid QD-in-perovskite approach