Quantitative Electrochemical Control over Optical Gain in Quantum-Dot Solids

Abstract

Solution-processed quantum dot (QD) lasers are one of the holy grails of nanoscience. They are not yet commercialized because the lasing threshold is too high: one needs >1 exciton per QD, which is difficult to achieve because of fast nonradiative Auger recombination. The threshold can, however, be reduced by electronic doping of the QDs, which decreases the absorption near the band-edge, such that the stimulated emission (SE) can easily outcompete absorption. Here, we show that by electrochemically doping films of CdSe/CdS/ZnS QDs, we achieve quantitative control over the gain threshold. We obtain stable and reversible doping of more than two electrons per QD. We quantify the gain threshold and the charge carrier dynamics using ultrafast spectroelectrochemistry and achieve quantitative agreement between experiments and theory, including a vanishingly low gain threshold for doubly doped QDs. Over a range of wavelengths with appreciable gain coefficients, the gain thresholds reach record-low values of ∼1 × 10 –5 excitons per QD. These results demonstrate a high level of control over the gain threshold in doped QD solids, opening a new route for the creation of cheap, solution-processable, low-threshold QD lasers.

Electrochemical p-Doping of CsPbBr3 Perovskite Nanocrystals

“… 25 , 26 This could allow, for instance, rational design of pn junction LEDs 27 − 29 or low threshold lasers. 30 …”

“…Since the discovery of lead halide perovskite nanocrystals (NCs) in 2014, these materials have been investigated as candidates for downconversion phosphors, − absorber layers in solar cells, − and emitting layers in light-emitting diodes (LEDs). − Important advantages of perovskite NCs are their facile synthesis − and their intrinsic defect tolerance. − As with all semiconductor materials, controlling the carrier density via electronic doping is key to tailoring the optoelectronic properties and implementation in devices. , This could allow, for instance, rational design of pn junction LEDs − or low threshold lasers …”

“…25,26 This could allow, for instance, rational design of pn junction LEDs 27−29 or low threshold lasers. 30 However, electronic doping is often challenging, and effects like doping compensation or self-purification can prevent control over the carrier concentration. 31,32 Especially for perovskites, which are complex compound semiconductors with a low stability, changing the Fermi level via doping could have many effects, including the decomposition of the material itself.…”

Electrically Pumped QD Light Emission from LEDs to Lasers

“…47 Both approaches, however, involve low oscillator strength transitions that sacrifice material gain to obtain a long inverted state lifetime and a low gain threshold. More recently, electrochemical doping of CdSe/CdS or chemical doping of PbS CQDs was successfully explored as a method to reduce the gain threshold, 48,49 yet stimulated emission still involves a multi-exciton state prone to rapid Auger recombination. Finally, theoretical considerations highlighted the possible impact of exciton-phonon coupling, which can yield single exciton gain when combined with biexci- ton repulsion, not unlike organic dyes.…”

An Investigation of Optical Gain of Nanomaterial AlGaAsIn/InP under CTLSs in Optical Communications

“…It has been clear that, now a day in the nano technological electronics and optical communication the yielding of optical gain [6,8,9,11] has substantial role due its unique light properties. Commonly, the profit in optical light is given by yielding of light per unit original light intensity and per unit length of active region of structure.…”