| Nanocrystals have been discussed among various I2-II-IV-VI4 semiconductors many times, the quintuple nanocrystals also be prepared by doping method in order to study their optical properties in this experiment. The studies on NCs with different compositions are mainly focused on NCs’ optical properties, and linearly tuned band gaps. At the same time, quite deficient information on the electrical characteristic of wurtzite NCs has been released.In this experiment, wurtzite and kesterite NCs are produced by different anion sources in order to compare the electrical differences between the two compounds.In this thesis, the NCs are produced by hot-injection. Then dispersions of NCs in non-polar solvents can be directly applied onto(Mo)-coated soda lime glass substrates to form film samples. Then high-temperature sintering is used to remove oleylamine, and then their electrical properties are tested.After compared the two kinds of film samples, it is found that the electrical properties, including illuminated and dark current density, as well as Iphoton/Idark, are all higher for the hexagonal structure than the tetragonal one. The advantages conferred by the wurtzite structure can now be extended from certain compounds to all Cu2Zn(Sn1-x Gex)S4 semiconductors, even possibly to the entire I2–II–IV–VI4 system, it provides references to study the application of their optical properties.When the lights, is incident or project, on the nanoparticles which constituted by noble metal element, if the frequency of the incident photon matches the overall vibration frequency of noble metal nanoparticles or metal islands’ conduction electrons, they would have a very strong photon energy absorption, and hence leads to the Localized Surface Plasmon Resonance(LSPR).Several semiconductor nanocrystals(NCs), such as binary copper chalcogenides Cux Sy, WO3-&, AZO, tin-doped indium oxide(ITO), and Ge Te, have been demonstrated to be capable of supporting Localized Surface Plasmon Resonances(LSPR) introduced by collective oscillations of free charge carriers. Wherein, binary copper chalcogenides, namely Cu2-x S, Cu2-x Se, Cu2-x S1-y Sey, Cu2-x Te, etc., are more thoroughly scrutinized as they show relatively strong LSPR in near-infrared region(NIR), originating from the Cu vacancies(VCu) which are considered as p-type dopant. In addition to the redox reaction, tunable LSPR could also be observed through altering size, stoichiometry, shape, crystal structures, or capping ligands.Recently, LSPR has been discovered in Cux Iny S2(CIS) quantum dots(QDs) by Rosenthal et al., and inherent plasmonic modes are supposed to be raised by intrinsic crystalline vacancy defects. Within the Cu–Sn–S system, Su and coworkers use successive ionic layer absorption(SILAR) to fabricate Cu2 Sn S3, Cu5Sn2S7, and Cu3 Sn S4 thin films, and interestingly, NIR absorption peaks are revealed. However, no appropriate explanation for such absorption is given so far.In this thesis, we report orthorhombic Cu3 Sn S4 NCs with NIR absorption which can be attributed to LSPR, and to the best of our knowledge, this is the first time for this phenomenon to be discussed for Cu–Sn–S family. In this experiment, we adjust the ratio of Cu/Sn to change the NCs’ inner free carrier density, it is found that LSPR frequency slightly red shifts and LSPR bands weaken. It is indicated that when the stoichiometry turns from Cu/Sn<3 to Cu/Sn>3, more Cu Sn antisites are produced which are detrimental for LSPR. It is also noted that higher carrier density of Cu3 Sn S4 NCs plays a decisive role in presenting a relatively stronger NIR absorption.Moreover, LSPR is also verified in Cu2 Sn S3 nanocrystals, and Cu2 Zn Sn S4 presents almost no absorption. In this experiment, we campared the three kinds of NCs, it is also found that LSPR frequency slightly red shifts and NIR absorption intersity weakens. Drude model is used to calculate the inner free carrier concentration, as a result of calculation, the carrier concentration of the two ternary compounds are on the same order which bigger than CZTS, little absorption in NIR is detectable in CZTS NCs due to its lower hole density. |
PDF Full Text Request