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Improvment of Perovskite Layer and Perovskite/Hole Transport Layer Interface to Inhance Perovskite Solar Cell Performance

Taherianfard, Hossein | 2021

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 55136 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Taghavinia, Nima; Tajabadi, Fariba
  7. Abstract:
  8. The use of renewable energy sources has received much attention due to the increasing need for energy, limited energy resources and the pollution of fossil fuels. Among all types of solar energy conversion technology, photovoltaics has the highest technical potential and Iran’s geographical location is very suitable for benefiting from this energy. So, in this thesis, the fabrication and characterization of nanostructured solar cells based on organic-inorganic perovskites have been investigated. Many research goups have tried to increase the efficiency of perovskite solar cells. The efficiency of this kind of solar cells depends mainly on the light-absorbing layer (perovskite) and its interface with other layers. Among depostion methods of perovskite, the solvent engineering technique is the most widely adopted which is also well-known as the anti-solvent method. The anti-solvent method induces an abrupt reduction in the solubility of the perovskite precursors, resulting in high nucleation density in the solution. Several challenges are associated with this method, such as randomly formed and distributed perovskite crystals, which decrease the photovoltaic performance. Despite some efforts to study the anti-solvent method in depth, knowledge of how the anti-solvent method can be used to deliberately control the nucleation and crystal growth steps remains scarce. In this thesis we try to explain how this method works based on classical nunleation theory and increase the power converstion efficiency as well. Chlorobenzene (as an anti-solvent) temperature affects the nucleation process which results in perovskite layer with different properties. By optimizing the chlorobenzene temperature, the perovskite layer with the lowest trap density is obtained, which leads to an increase in power conversion efficiency. Spiro-OMeTAD has been used as hole transport layer (HTL) in many studies. However, the interfacial contact problem between perovskite and Spiro- OMeTAD is still an open topic. Researchers have introduced different kinds of modifiers to improve this interface. In this thesis, we report a facile way to improve the interface between the perovskite layer and HTL by replacing a small amount of chlorobenzene (CB) with acetonitrile (ACN) in Spiro-OMeTAD solution. Normally the Spiro-OMeTAD solution is spin coated onto the perovskite layer which causes a relatively poor contact between two layers. To improve this contact, we dissolved Spiro-OMeTAD in a mixture of CB and ACN with 4 to 1 ratio instead of pure CB. After pouring the Spiro-OMeTAD solution onto the perovskite layer, we waited for various times before starting the spin coating process. With the passage of time, ACN dissolves the surface of perovskite layer and after spinning a mixed layer of perovskite/HTL formed. We found that the contact between the two layers improves up to about 40 s resting time of the HTM solution. By using this method, a PCE of 19:7% with negligible hysteresis was obtained
  9. Keywords:
  10. Hole Transporter Layer ; Crystal Growth ; Nucleation ; Temperature ; Perovskite-Based Solar Cell ; Antisolvent Spin-Coating ; Acetonitrile ; Spiro-Ometad

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