Enhanced Electronic Properties in Mesoporous TiO2 Via Passivation Treatment in Perovskite Solar Cells

Azadi, Moloud | 2019

656 Viewed
  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 51934 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Mohammadi, Mohammad Reza
  7. Abstract:
  8. Perovskite solar cells are the new generation of solar cells, and are mainly introduced in two types of structures.1) planer and 2) mesoscopic structure. The difference between these two structures derives from the absence of mesoporous layer in the planer structures. The mesoporous layer acts as an electron transporting layer, and is mainly a titanium dioxide semiconductor. To apply the mesoporous layer, the preparation of the TiO2 paste is needed.The synthesis of titanium dioxide nanopowder for the preparation of TiO2 paste requires high temperature heat treatment and is not desirable in terms of energy consumption.Another weakness of this layer is the presence of surface defects, which leads to the trapping of the generated electron and increases the recombination. In this research, in order to eliminate the heat treatment step in TiO2 nanopowder synthesis process, pure TiO2 paste was prepared using TiO2 sol and polymeric material like PEG. After optimizing the PEG content and the spin coating parameters of the TiO2 mesoporous layer, the problem of the electronic traps in the TiO2 mesoporous film was eliminated by: 1) doping of the یون Li salt in TiO2 paste by sol-gel method. And 2) passivation of the mesoporous TiO2 layer via applying the Li-TFSI layer. Optical, structural and morphological properties of pure titanium film and doped with یون Li salt by X-ray diffraction (XRD), scanning electron microscopy (FESEM), UV-Vis spectroscopy and diffuse Reflection Spectrometry (DRS) were examined. also the effect of doping and passivation treatment on recombination in the mesoporous film by photoluminescence spectrometry (PL) and the photovoltaic properties of the solar cells by the voltage-current measurments were determined. XRD results showed the crystallization of both anatase and rutile phases in a pure and doped TiO2 crystalline structure. FESEM images confirm the uniform structure of the thin TiO2 film.The results of the Vis UV and DRS showed that the doping of the lithium in content of 3 and 5(at%) reduced the band gap of TiO2 and when the amount of lithium doped increased,due to the unsuccessful doping of lithium in TiO2 crystalline structure, the band gap, in comparison with the pure TiO2, did not change significantly. PL spectrophotometry showed that the most reduction in recombination was calculated for the Li-TFSI passived mesoporous film. However, the reduction of recombination in 3 and 5 at% doped film was observed, while in 7 and 9 at% lithium doped mesoporous films, the recombination, due to the decrease in the size of TiO2 nanoparticles, and increasing the defects of the crystalline TiO2, increased. The photovoltaic properties of solar cells also showed that, beside of the increasing the values of the open circuit voltage as a result of the reduction of recombination in Li-TFSI passived and doped with 3 and 5 at% mesoporous films, the short circuit photocurrent density of the Li-TFSI passived and doped with 3at% Li +,increased due to the increasing the light scattering by rutile phase crystals and also the reduction of the band gap caused by the lithium doping. Improvement of two photovoltaic parameters including open circuit voltage and short circute current density together in perovskite cell-solar cell based on 3at% Li doped TiO2 and Li-TFSI passived films, respectively, increased the efficiency of the solar cell by 94 and 100 % in comparison with solar cell pased on pure TiO2 mesoporous film
  9. Keywords:
  10. Perovskite-Based Solar Cell ; Pure Titanium Dioxide Paste ; Lithium Doping ; Surface Treatment ; Mesoporous Titanium Dioxide

 Digital Object List