جلسه دفاع از رساله: آقای حسین حسین، گروه فیزیک جامدات

خلاصه خبر: بررسی خواص اپتو الکتریکی ومغناطیسی سولفیدهای فلزی چهار گانه در حضور عناصر مغناطیسی

  • عنوان: بررسی خواص اپتو الکتریکی ومغناطیسی سولفیدهای فلزی چهار گانه در حضور عناصر مغناطیسی
  • ارائه‌کننده: حسین حسین
  • استاد راهنما: دکتر احمد یزدانی
  • مکان: اتاق همایش واقع در طبقه 1 - دانشکده علوم پایه
  • تاریخ: چهارشنبه 17/11/97
  • ساعت: 15

چکیده Recently, quaternary Cu2ZnSnS4 (CZTS) semiconductor has garnering attention in the CZTS thin film solar cell. In order to improve the opto-electrical properties of the CZTS thin film which in turn will enhances the conversion efficiency of the CZTS solar cell, principle of change the ionic radius and electronegativity into the CZTS compound have been investigated. It was observed that the ionic radius and electronegativity are two important factors have a significant impact on the crystal structure, morphology of particles and optoelectrical properties of the particles. Also, decreasing and/or increasing the ionic radius led to difference the applied strain inside the crystalline structure resulting in different the lattice parameters and then the particle size. In addition, increasing the electronegativity in the crystal structure led to increase the ionic interaction between cation-anion resulting in increasing the hybridization and then its impact on the optical band gap. This principle has been applied for the first time using the full and partial substitution process of Zn (II) element with Cr (III), Fe (III), Bi (III) and Cr (II) elements respectively. Due to the great influence of these elements on the CZTS crystal making it that have a major and noticeable interest for improving the optoelectrical properties of the CZTS thin film. So that, in this regard, the multicomponent chalcogenide Cu2(Zn1-xMx)SnS4 (CZMTS) nanoparticles and thin films at x= 0, 0.25, 0.5, 0.75 and 1 were synthesized and fabricated by the solvothermal and spin coating methods respectively, where "M" is Cr (III), Fe (III), Bi (III) and Cr (II). XRD patterns, Raman spectra, UV-Vis spectra, PL spectra, FESEM, I-V curve and VSM have been investigated. XRD patterns reveals that when Zn element substituted with "M" elements, the crystallinity of the CZMTS nanocrystals has been improved accompanied by increasing the crystal size. Also, substituting Zn element with the "M" elements led to change the applied strain inside the crystal and the lattice parameters resulting in dropping the disorder of cations distribution in the unit cell which resulted in decreasing the unit cell volume. Raman analysis showed that the bond length and the bond strength have been changed depending on the ionic radius. It was observed one significant peak at 338 cm-1 corresponding to pure anion A1 vibrational mode of the CZTS phase. This peak was shifted towards smaller frequencies when Zn element substituted with "M" elements. Also, Raman spectra reveals that, there are no secondary phases have been observed, after substituting Zn element with Cr and Fe elements except Bi element. Additional characteristic Raman peaks have been detected when Zn element replaced with Bi element. The intensity and position of these peaks have changed and consistent with the reported for the Cu3BiS3 phase. UV-Vis absorption spectra showed that the electronegativity of the ions has great impact on the hybridization of cations-anions and shrinking the optical band gap which clearly affects the absorption spectra. It was observed the absorption intensity in the range of 200-1000 nm wavelengths has been increased by substituting Zn element with "M" elements. Also, increasing the full and partial substitution of Zn element with "M" elements led to dropping the optical band gap from 1.54 eV for the CZTS to 1.35 eV, 1.27 eV, 1.049 eV and 1.25 eV for the CCr3+TS, CFTS, CBiTS and CCr2+TS respectively. In addition, it was noted the absorption coefficient, optical conductivity and refractive index of the CZTS thin film have been increased accompanied by decreasing the transmittance of the thin films with increasing substituting Zn element with "M" elements. PL spectra of the CZTS nanoparticles confirmed decreasing the intrinsic defects resulting in increasing the absorption coefficient and optical conductivity by substituting Zn element with "M" elements. Furthermore, FESEM showed that morphology of the CZTS nanoparticles was sphere-like particles. These sphere-like particles have been changed to rod-like and sheet-like when Zn element substituted with Fe element. Also, these sphere-like particles have been changed to flower-like and to rod-like particles when Zn element replaced with Bi element. This changing in the morphology of particles is due to the applied strain on the CZTS crystal and may help to improve the optical properties of the films. In addition, FESEM showed the micrographs of the CZTS thin film was non-uniform film and had creaks which are what makes the transmittance of the film seems to be high. After substituting Zn element with "M" elements, the films have become more uniform, coalesced and improved than the CZTS film. It was observed that the number of grains in the CZTS thin film was 6.8 nm-2 whereas it's become 2.79 nm-2, 5.9 nm-2, 0.038 nm-2 and 4.2 nm-2 in the CCr3+TS, CFTS, CBiTS and CCr2+TS thin films respectively. Also, the dislocation density in the CZTS thin film was 0.024 nm-2 whereas it's become 0.012 nm-2, 0.022 nm-2, 0.0007 nm-2 and 0.019 nm-2 in the CCr3+TS, CFTS, CBiTS and CCr2+TS thin films respectively. I-V curve reveals that decreasing the number of grains and dislocation density led to decrease the defects on the grain boundaries and hence increasing the current from 0.34 Ma for the CZTS thin film to 0.42 mA, 0.45 mA, 0.48 mA and 0.64 mA for the CCr3+TS, CFTS, CBiTS and CCr2+TS thin films respectively. Finally, the magnetic properties of the CZMTS nanoparticles were investigated by VSM. A paramagnetic behavior has been observed for the CZTS nanoparticles ascribe to the presence of unpaired electrons between Sn and S. After the partial substitution of Zn element with "M" elements, the magnetization of the samples has increased as straight lines indicating that the samples are paramagnetic materials. Also, after the full substituting Zn element with "M" elements, superparamagnetic and ferromagnetic behaviors have been observed which attributed to the exchange interaction between localized "d" spins on the "M" ions and free delocalized carriers. Due to a high absorption coefficient, a high optical conductivity and lower transmittance have been reported for the CCr3+TS, CFTS, CBiTS and CCr2+TS thin films than that of CZTS thin film, we believe that these thin films can be considered as novel materials and competitors for the CZTS material to be used as an absorbent layer to sunlight in thin film solar cell.
کلمات کلیدی kesterite and stannite structures, Solvothermal method, Spin coating, Optoelectrical properties, Transition metal dopant, Opto-magnetic property, CZTS thin film and Thin film solar cell.


3 بهمن 1397 / تعداد نمایش : 1451