Advanced Technology and Manufacturing Institute (ATAMI)

The need for less toxic quantum dots (QDs) has led to a significant number of investigations related to copper indium sulfide (CIS) QDs. Lower toxicity and broad band absorbance width makes CIS QDs appealing for light emitting diodes (LEDs), lasers, sensors, bio-imaging, solar cells, and computing. The optical and electronic properties of CIS QDs can be modified by varying their size, composition, and surface characteristics. CIS QDs with 1:1, 1:2, and 1:5 Cu:In ratios were synthesized, and their optical and chemical properties were investigated using UV-Vis, spectrofluorometry, Raman, and Fourier transform infrared (FTIR) spectrometry. The composition of the as synthesized CIS QDs were determined by energy dispersive spectroscopy (EDS), and their size, shape, and crystal structure were determined by using high resolution transmission electron microscope (HR-TEM). The as synthesized samples had compositions similar to the reaction precursors. Decreasing the QDs Cu:In ratio from 1:1 to 1:2 and 1:5 resulted in a blue shifted emission from 664 nm to 640 nm and 638 nm, respectively. The excitonic peak in the absorbance spectra shifted to higher energy with decreasing the Cu:In ratio. The 1:2 Cu:In ratio resulted in the highest photoluminescence quantum yield (PLQY), where the PLQY increases with Cu vacancies up to the 1:2 Cu:In ratio QDs and decreases afterward due to reabsorption. The as synthesize CIS QDs core surface was treated with an organic super acid to improve the surface states. The treated CIS core QDs PLQY increased by more than 50%, compared to the untreated CIS core QDs, without affecting the optical properties. The organic super acid treated CIS QDs core was further passivated with ZnS and the resulting hybrid surface passivated CIS/ZnS QDs showed a PLQY improvement over 66%. No significant change in size, shape, composition, emission band, and absorption properties were observed for organic super acid treated CIS QDs. The super acid improved the PLQY without significantly affecting optical, structural, and chemical properties of CIS QDs.