Colloidal Quantum Dot Light Emitting Diodes at Telecom Wavelength with 18% Quantum Efficiency and Over 1 MHz Bandwidth.

Developing high performance, low-cost solid-state light emitters in the telecom wavelength bandwidth is of paramount importance for infrared light-based communications. Colloidal quantum dot (CQD) based light emitting diodes (LEDs) have shown tremendous advances in recent times through improvement in synthesis chemistry, surface property, and device structures. Despite the tremendous advancements of CQD based LEDs in the visible range with efficiency reaching theoretical limits, their short-wave infrared (SWIR) counterparts mainly based on lead chalcogenide CQDs, have shown lower performance (≈8%).

Visible-Blind ZnMgO Colloidal Quantum Dot Downconverters Expand Silicon CMOS Sensors Spectral Coverage into Ultraviolet and Enable UV-Band Discrimination.

Selective spectral detection of ultraviolet (UV) radiation is highly important across numerous fields from health and safety to industrial and environmental monitoring applications. Herein, a nontoxic, visible-blind, quantum dot (QD)-based sensing scheme that expands the spectral coverage of silicon complementary metal-oxide-semiconductor (CMOS) sensors into the UV, enabling efficient UV detection without affecting the sensor performance in the visible and UV-band discrimination, is reported. This scheme uses zinc magnesium oxide (ZnMgO) QDs with compositionally tunable absorption across UV and high photoluminescence quantum yield in the visible.

Solid-State Thin-Film Broadband Short-Wave Infrared Light Emitters.

Solid-state broadband light emitters in the visible have revolutionized today's lighting technology achieving compact footprints, flexible form factors, long lifetimes, and high energy saving, although their counterparts in the infrared are still in the development phase. To date, broadband emitters in the infrared have relied on phosphor-downconverted light emitters based on atomic optical transitions in transition metal or rare earth elements in the phosphor layer resulting in limited spectral bandwidths in the near-infrared and preventing their integration into electrically driven light-emitting diodes (LEDs). Herein, phosphor-converted LEDs based on engineered stacks of multi-bandgap colloidal quantum dots (CQDs) are reported as a novel class of broadband emitters covering a broad short-wave infrared (SWIR) spectrum from 1050-1650 nm with a full-width-half-maximum of 400 nm, delivering 14 mW of optical power with a quantum efficiency of 5.

Single-Exciton Gain and Stimulated Emission Across the Infrared Telecom Band from Robust Heavily Doped PbS Colloidal Quantum Dots.

Materials with optical gain in the infrared are of paramount importance for optical communications, medical diagnostics, and silicon photonics. The current technology is based either on costly III-V semiconductors that are not monolithic to silicon CMOS technology or Er-doped fiber technology that does not make use of the full fiber transparency window. Colloidal quantum dots (CQDs) offer a unique opportunity as an optical gain medium in view of their tunable bandgap, solution processability, and CMOS compatibility.

Low-Cost RoHS Compliant Solution Processed Photovoltaics Enabled by Ambient Condition Synthesis of AgBiS Nanocrystals.

Two major challenges exist before colloidal nanocrystal solar cells can take their place in the market: So far, these devices are based on Pb/Cd-containing nanocrystals, and second, the synthesis of these nanocrystals takes place in an inert atmosphere at elevated temperatures due to the use of air-sensitive chemicals. In this report, a room-temperature, ambient-air synthesis for nontoxic AgBiS nanocrystals is presented. As this method utilizes stable precursors, the need for the use of a protective environment is eliminated, enabling the large-scale production of AgBiS nanocrystals.

Origin of the Below-Bandgap Turn-On Voltage in Light-Emitting Diodes and the High V in Solar Cells Comprising Colloidal Quantum Dots with an Engineered Density of States.

The turn-on voltage of a light-emitting diode (LED) is an important parameter as it determines the power consumption of the LED and influences the effective power conversion efficiency. LEDs based on nanoscale engineering of the blended PbS [mixture of quantum dots (QDs) with two different bandgaps] colloidal QDs have recently shown record performance in the infrared region. One of the most intriguing findings for these blended devices is the substantially lower-than-bandgap turn-on voltage and the achievement of an open circuit voltage ( V), approaching the radiative limit.

Solution processed infrared- and thermo-photovoltaics based on 0.7 eV bandgap PbS colloidal quantum dots.

Harnessing low energy photons is of paramount importance for multi-junction high efficiency solar cells as well as for thermo-photovoltaic applications. However, semiconductor absorbers with the bandgap lower than 0.8 eV have been limited to III-V (InGaAs) or IV (Ge) semiconductors that are characterized by high manufacturing costs and complicated lattice matching requirements in their growth and integration with higher bandgap cells.

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.

Infrared Solution-Processed Quantum Dot Solar Cells Reaching External Quantum Efficiency of 80% at 1.35 µm and J in Excess of 34 mA cm.

Developing low-cost photovoltaic absorbers that can harvest the short-wave infrared (SWIR) part of the solar spectrum, which remains unharnessed by current Si-based and perovskite photovoltaic technologies, is a prerequisite for making high-efficiency, low-cost tandem solar cells. Here, infrared PbS colloidal quantum dot (CQD) solar cells employing a hybrid inorganic-organic ligand exchange process that results in an external quantum efficiency of 80% at 1.35 µm are reported, leading to a short-circuit current density of 34 mA cm and a power conversion efficiency (PCE) up to 7.

Reducing Interface Recombination through Mixed Nanocrystal Interlayers in PbS Quantum Dot Solar Cells.

The performance of ZnO/PbS colloidal quantum dot (CQD)-based heterojunction solar cells is hindered by charge carrier recombination at the heterojunction interface. Reducing interfacial recombination can improve charge collection and the photocurrent of the device. Here we report the use of a mixed nanocrystal (MNC) buffer layer comprising zinc oxide nanocrystals and lead sulfide quantum dots at the respective heterojunction interface.

Trap-State Suppression and Improved Charge Transport in PbS Quantum Dot Solar Cells with Synergistic Mixed-Ligand Treatments.

The power conversion efficiency of colloidal PbS-quantum-dot (QD)-based solar cells is significantly hampered by lower-than-expected open circuit voltage (V ). The V deficit is considerably higher in QD-based solar cells compared to other types of existing solar cells due to in-gap trap-induced bulk recombination of photogenerated carriers. Here, this study reports a ligand exchange procedure based on a mixture of zinc iodide and 3-mercaptopropyonic acid to reduce the V deficit without compromising the high current density.