Efficient White-Light-Emitting Diodes Fabricated from Highly Fluorescent Copper Indium Sulfide Core/Shell Quantum Dots

Abstract

Copper indium sulfide (CIS) quantum dots (QDs) with different Cu/In molar ratios of 1/1, 1/2, and 1/4 are synthesized via a hot colloidal route. The band gap energy of CIS QDs is observed to be dependent on Cu/In ratio, exhibiting a higher band gap from more Cu-deficient QDs. The emission wavelengths of all CIS QDs belong to a deep red region (665–717 nm) with relatively low quantum yields (QYs) of 8.6–12.7%. Compared to respective original core QDs, the absorption peaks of all CIS/ZnS QDs are blue-shifted, and their emission wavelengths move to a higher energy accordingly, showing a quite tunable emission from yellow to red. The effective surface passivation by a ZnS overlayer results in a dramatic increase in QY of CIS/ZnS QDs in the range of 68–78%. All CIS/ZnS QDs are tested as wavelength converters for the fabrication of QD-based light-emitting diodes (LEDs). QD-based white LEDs that consist of only a single type of QD are for the first time realized by applying yellow-emitting CIS/ZnS QDs as a result of the appropriate color mixing between blue emission from a LED chip and yellow emission from QDs. Detailed electroluminescent properties including color rendering index, Commission Internationale de l’Eclairage (CIE) color coordinates, and luminous efficiency of QD-based white LEDs are evaluated as a function of forward current.

Low-Temperature Approach to Highly Emissive Copper Indium Sulfide Colloidal Nanocrystals and Their Bioimaging Applications

“…Such an increase from Sample 5 (120°C/15 min) to Sample 11 (160°C/120 min) is similar to what was observed during the growth of Zn x Cd 1−x S gradiently alloyed QDs 43 and CdTe/CdSe core−shell QDs. 44 Figure S1B in the Supporting Information demonstrates the good synthetic 3 -to-4SDPP feed molar ratios. The growth was at 160°C for 120 min, and the PL QY was estimated to be ∼23% for the as-synthesized NCs.…”

“…It should be pointed out that, for the eq 1 approach, the Cu and In precursors could be in the form of Cu-SR and [In]-(SR) n (n =1 −3, RSH = DDT), respectively, after the two mixtures of CuI and DDT, and In(OAc) 3 and DDT were kept at 65°C under a strong vacuum (∼50 mTorr) for at least 1 h. We symbolize preferably CuI/DDT as the Cu precursor and In(OAc) 3 /DDT as the In precursor, due to the possible presence of I − and OAc − without purification. Furthermore, being a sulphur precursor, SDPP is much more reactive than DDT, as evidenced by the substantial decrease in nucleation temperature.…”

“…Furthermore, being a sulphur precursor, SDPP is much more reactive than DDT, as evidenced by the substantial decrease in nucleation temperature. As shown in Figure S1C (top left) in the Supporting Information, with DDT as a sulphur source and with CuI and In(OAc) 3 as the respective Cu and In sources, the nucleation of CuInS 2 NCs in ODE took place at ∼180°C. Therefore, the optimal growth temperature with SDPP as the sulfur source could be reduced to 160°C, which is appreciably lower than the typical CuInS 2 NC growth temperature of 200− 240°C.…”

“…The resulting CuInS 2 NCs are gradiently-alloyed with Cu locating more on the inner part and In more on the outer layer. Both in situ highresolution 31 P NMR with 1 H decoupling and in situ absorption measurements testify that the reactivity of CuI/DDT toward SDPP in DDT is lower than that of In(OAc) 3 /DDT. Furthermore, in situ high-resolution 31 P NMR suggests that the combination of Cu−S and In−S monomers leads to nucleation/growth of the alloyed CuInS 2 NCs, as shown in Scheme 1.…”

“…To the best of our knowledge, the present study is the first using SDPP to synthesize CuInS 2 NCs at temperature as low as 160°C. Extensive optimization of experimental parameters such as various Cu (I), Cu (II), and In (III) source compounds, Cu-toIn-to-SDPP feed molar ratios, SDPP concentrations, and alternative solvents/ligands (including ODE, oleic acid (OA), and oleylamine (OLA)) suggested an optimal approach in DDT with the feed molar ratio of 1CuI-to-1In(OAc) 3 -to-4SDPP, as shown by eq 1. The resulting CuInS 2 NCs dispersed in toluene exhibited QY as high as 23%.…”