Preparation, Characterization And Photovoltaic Application Of CuInSe 2 Chalcopyrite Thin Films By Nanocrystal Colloidal Ink Technique

CuInSe₂ (CIS) chalcopyrite compound is an important photo-absorbing semiconductor in the development field of thin film solar cells. Recent years, nanocrystal colloidal ink technique has been applied to prepare CuInSe₂ based chalcopyrite absorbing layers for its cheaper fabrication cost and improvement of environmental pollution related to"selenium vapor reaction". In this dissertation, CuInSe₂ nanoparticles were synthesized by solution chemical methods using 1-Methyl-2-pyrrolidinone (NMP) hot-solvent and NMP/Glycerin mixed solvent reaction medium, respectively. CuInSe₂ inks were prepared by using ethanol solvent and CuInSe₂ thin films were deposited on glass substrates by dip-coating method using its colloidal inks. The CuInSe₂ nanoparticles, inks and thin films were characterized by XRD, FESEM, TEM, HRTEM, EDS, XPS, UV-vis-NIR. The synthesis system and chemical reaction mechanism were discussed. The CuInSe₂ thin film was used to assemble experimental photovoltaic devices with cell structure of ITO/CdS/CuInSe₂/counter electrode and current-voltage characteristics were measured.The research results showed that the CuInSe₂ nanoparticles synthesized by hot-solvent method using 1-Methyl-2-pyrrolidinone (NMP) as hot-solvent were phase-pure chalcopyrite with well crystallinity. The particle size was in the range of 30⁵0nm. The shape of nanoparticles was polygonal. The stoichiometry of nanoparticles was consistent with the precursor element ratios in reaction solutions. In the reaction process, the reduction process of Se was Se⁴⁺→Se⁰→Se^2-, and there was intermediate phase Cu_2-xSe in the reaction process.In preparation process of CuInSe₂ nanoparticles by the hot injection method, the appropriate volume ratio of NMP/Glycerin mixed solvent was 1:2. The optimum of holding time was 20min. A little residual amount of element Se was presented and the particle size of nanoparticles was non-uniform when the nanoparticles was synthesized under low injecting/refluxing temperature. The nanoparticles prepared in high injecting/refluxing temperature were phase-pure chalcopyrite, and the particle size was more uniform. The stoichiometry of CIS nanocrystals was also consistent with the precursor element ratios in reaction solutions.After annealed under 500℃for 20min, the CuInSe₂ thin films prepared by ink coating process were phase-pure. The CIS thin films from nanocrystal inks synthesized under 190℃/170℃had the best density and optical property. The stoichiometry of thin films was consistent with the element ratios in the inks, and the change of stoichiometry had no effects on the surface morphology of thin films. When stoichiometry of CIS thin film was close to 1:1:2, the band gap energy Eg of thin film was close to1.04. The high annealing temperature could improve the crystallinity of the thin films, but if the annealing temperature was over 600℃, some defects would appear in the thin films. The cyclic annealing could not improve the quality of thin films.The current-voltage curve of CdS/CuInSe₂ heterogeneous structures is non-linear. In the dark, the experimental photovoltaic devices had a small short-circuit current(7μA/cm²). Under illumination, the open-circuit voltage, short-circuit current and the highest fill factor was 135mV, 27μA/cm² and 22.67%, respectively.