Preparation And Study Of CuIn_xGa_1-xS₂ Quantum Dots

In recent years, quantum dots?QDs? have drawn much attention due to their tunable optical and electronic properties as well as their promising application in nanodevices. Cu InS₂ QDs, with high absorption coefficient?105 cm-1?, direct band gap of 1.50 eV and non-toxicity, was a kind of promising solar cell material. While the emission range of CIS QDs was limited due to its band gap, how to broaden the region of fluorescence emission and promote the application in more fields demanded immediate attention.In this work, chalcopyrite ternary Cu InS₂ QDs and CuGaS₂ QDs and quaternary CuIn_xGa_1-xS₂ QDs, with tunable size, composition and optical properties, were synthesized through hot injection method that was simple, safe, low cast, and environmentally friendly. The structures and the morphologies of the as-synthesized quantum dots were characterized by XRD, TEM, HTEM, FTIR and EDS. The optical properties were investigated by UV-vis absorption and photoluminescence spectra.In the synthesis process of CIS QDs, the quality of products depended to a large extent on an appropriate reaction time that is closely linked with the nucleation and growth of nanoparticles. Here, we investigated the influence of reaction time on the crystal growth and optical properties of CIS QDs at 230?. By prolonging reaction time, XRD patterns tended to be more distinct, reduced noise and narrow FWHM, which indicated the better crystallinity and larger particle size. The UV-vis absorption and PL spectra were both apparent red shift during the 100 minutes repectively showing the effects of quantum confinement, which indirectly proved the particles increasing gradually by extending reaction time. Therefore, the size and emission wavelength of CIS QDs can be tuned by adjusting the reaction time effectively.Chalcopyrite CuGaS₂ QDs were obtained at temperatures ranging from 210? to 260?. The size of CuGaS₂ nanoparticles could be tuned by varying the reaction temperature, with the resulting size-dependent absorption and photoluminescence spectra red shift showing the effects of quantum confinement. A detailed investigation of the growth process by monitoring the structures, morphologies and molar ratio of elements of the QDs during the growth indicated that the monodispersed hexagonal nanocrystals were formed and nanoparticles aggregated together when temperature was raised to 250?.CuIn_xGa_1-xS₂?x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0? QDs were synthesized under the same conditions. Our results indicated that the synthesized materials were in the nano regime and had good crystallinity and tunned optical properties. The optical band gaps of the CuIn_xGa_1-xS₂ QDs were composition-dependent and the band gap tuning of the compounds could be adjusted from 1.61 eV for CIS QDs to 2.59 eV for CGS QDs which was a wide spectral region from visible?525nm? to near-infrared?754nm?.The leakage of traditional liquid electrolyte resulted in medium loss for charge transfer. A solution to this impasse was to develop all-solid-state electrolytes having high charge transfer ability and cost-effectiveness. Here, the solid-state quantum dots sensitized solar cells?QDSSCs? were assembled by sandwiching the Spiro-OMeTAD as the solid-state hole conductor between the Cu InS₂-sensitized TiO₂ anode and the Ag counter electrode. The self-assembled monolayer?SAM? approach was applied to adsorb the QDs by changing the time that the TiO₂ electrode immersed in the sensitized solution of CuInS₂ QDs. More importantly, this FTO/TiO₂/CIS/Spiro-OMeTAD/Ag structure could open a new way for the development of the QDSSCs.