Colloidal Synthesis of Ternary Copper Indium Diselenide Quantum Dots and Their Optical Properties

Abstract

Ternary direct semiconductor CuInSe2 quantum dots (QDs) with average particle sizes ranging from 1.2 to 5.6 nm have been synthesized by a colloidal route using commercially available materials. The size-dependent optical band gap and photoluminescence (PL) band shift due to the quantum size effect were successfully observed. The optical band gap evaluated from the optical absorption spectra was varied from 1.48 eV for the 5.6-nm QDs to 1.66 eV for the 1.2-nm QDs. In the PL spectra, the wavelength of the emission band varied from 918 to 838 nm corresponding to the crystal size variation from 5.6 to 1.2 nm. Because the PL band showed a large Stokes shift above 100 meV, the origin of the PL band was related to the electronic transition via defect levels. Based on the slightly In-rich composition of the QDs and the comparatively large increase in energy of the PL band with decreasing crystal size, the emission was suggested to be due to the recombination between electrons in the quantized conduction band and holes in the copper vacancy acceptor.

Noninjection, one-pot synthesis of Cu-deficient CuInS2/ZnS core/shell quantum dots and their fluorescent properties

“…Exact emission mechanism of these quantized CIS nanocrystals appears to be still controversial. This defect-related emission has been mostly attributed to the DAP recombination [6][7][8][9][10][11]14,16,17,19] whereas Nose et al proposed the electron-hole recombination between quantum-shifted 1S(e) and Cu vacancy (V Cu ) levels instead of DAP recombination to explain the tunable emissions of their CuInSe 2 QDs [18]. In the present CIS QDs, their emission peaks were red-shifted to a small extent for longer-reacted (i.e., larger sized) QD samples.…”

“…These deep traps can be a sulfur vacancy (V S ), an interstitial copper (Cu i ), and an indium substituted at a copper site (In Cu ) as donor states, and a copper vacancy (V Cu ), an indium interstitial (In i ), and a copper substituted at an indium site (Cu In ) as acceptor states. The particular type of these donor and acceptor states would depend on the stoichiometry of CIS, i.e., Cu-rich versus In-rich phases [10,14,[16][17][18], determining the dominant DAP recombination pathway. The population density of such defects can also be readily controllable in colloidal routederived CIS QDs.…”

Near‐Band‐Edge Electroluminescence from Heavy‐Metal‐Free Colloidal Quantum Dots

“…[ 21 ] Apart from the TRPL study, the insight to the emission mechanism of ZCIS QDs can also be gained from the observation that there is a pronounced spectral shift ( ∼ 67 nm or 340 meV) for PL emission as the size of the ZCIS cores of the QDs is reduced from 3.3 to 2.4 nm, which is too large for DAP recombination or for any radiative transition between a pair of deep levels. The size-induced PL shift for a DAP recombination comes only from the change in the Coulomb interaction with changing DAP separation, r , according to the equation [ 22 ] …”

Advancing colloidal quantum dot photovoltaic technology

“…These compounds include binary, mostly III-V and II-VI semiconductors such as metal chalcogenides [78][79][80], as well as ternary and quaternary compounds [81][82][83][84].…”