Near-Unity Quantum Yield in Semiconducting Nanostructures: Structural Understanding Leading to Energy Efficient Applications

Abstract

Core/shell nanocrystal quantum dots (NQDs) have shown great potential as efficient electroluminescent materials in devices like down-conversion phosphors and light-emitting diodes (LEDs). The efficiency of these devices is nonlinearly enhanced by the use of high quantum yield (QY) materials. Though relatively high QY materials with inherent advantages for use in device applications are achieved by thick-shell CdSe/CdS NQDs, their QY is not anywhere near unity due to lack of correlation of the microstructure with their photophysical properties. Here, in this Letter, we show that the control of interfacial defects is crucial to achieve a near-unity QY using microstructure studies of CdSe/CdS NQDs. Simple unoptimized LEDs obtained from these NQDs as the active layer demonstrate performances in excess of 7000 Cd/m 2 with a power conversion efficiency of ∼1.5 lm/W that is comparable to those of the best NQD-based LEDs (1−3%) despite the absence of an electron-injecting buffer layer. SECTION: Physical Processes in Nanomaterials and Nanostructures

Demystifying Complex Quantum Dot Heterostructures Using Photogenerated Charge Carriers

“…5,23 Charge carrier delocalization beyond the traditional boundaries of the core and/or shell is well known in literature due to change in material composition as well as energetics. In the current case, this red shift was observed in many literature reports 21,22 which predict a quasi type II nature of CdSe/CdS QDs wherein the electron is delocalized into CdS shell as a result of small CB offset. However, this quasi type II character does not completely explain the observed optical behavior.…”

“…This could be due to the need to maintain lower temperatures to retain Cu within the QD 20 while high temperature annealing for extended period of time is necessary for the formation of high quality heterostructures. 21 In this manuscript, we have synthesized Cu doped heterostructures by the appropriate use of ligands as well as suitable variation of temperatures. We have then shown that these Cu doped heterostructures can be used to 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 understand the charge localization in a range of heterostructure QDs including type I, type II, inverse type I, quasi type II QDs along with alloys and alloy shell heterostructures using Cu emission and absorption spectra.…”

Temperature-Dependent Exciton and Trap-Related Photoluminescence of CdTe Quantum Dots Embedded in a NaCl Matrix: Implication in Thermometry

“…[2][3][4][5][6][7][8][9] Compared with these materials, fl uorescent colloidal semiconductor quantum dots (QDs) are attractive optical probes due to the high photoluminescence (PL) quantum yield (QY), narrow emission, and multiparameter detectable signals. [10][11][12][13] Temperature-dependent studies of the optical properties of QDs have therefore become an emerging area of scientifi c research. Many of these studies are commonly performed at low temperatures to elucidate electronic and excitonic structure in the absence of thermal broadening, and to provide insights into the exciton relaxation processes and excitonphonon interactions.…”

Influence of Ag doping concentration on structural and optical properties of CdS thin film

“…Furthermore, due to high absorption coefficient, conversion efficiency, stability, and significantly low cost synthesis, CdS has continued to be the focus of research. Thin films of CdS have potential applications as solar cell material 2 , lasers 3 , photocatalyist 4 , gas-sensors 5 and light emitting diodes 6 . The extensively used approach to tune the emission range and improve the efficiency of optoelectronic devices is incorporation of impurity atoms in host materials.…”