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Surface Passivation of PbS Colloidal Quantum Dots for Photovoltaic Applications

Tavakkoli, Mohammad Mahdi | 2015

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 47354 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Simchi, Abdolreza; Ashuri, Hossein
  7. Abstract:
  8. Solution-processed quantum dots (QDs) have attracted significant attention for the low-cost fabrication of optoelectronic devices. Here, we synthesized PbS QDs via hot injection method and passivated the trap states by using short thiols and dopant elements for photovoltaic application. In order to study the effect of dopants on photovoltaic application, PbS QDs were doped by using three different cations: Cadmium, Calcium, and Zinc. The results showed that Cd dopant has a better improvement than Ca and Zn dopants in order to increase the efficiency of the PbS QDs solar cells. We achieved solar power conversion efficiencies of 5.81% using Cd therapy. Recently, hybrid nanocomposites consisting of graphene/nanomaterial heterostructures have emerged as promising candidates for the fabrication of optoelectronic devices. In this work, we have employed a facile and in-situ solution-based process to prepare zinc oxide/graphene quantum dots (ZnO/G QDs) in hybrid structure. The prepared hybrid dots are composed of ZnO core with an average size of 5 nm warped with graphene nanosheets. Spectroscopic studies show that the graphene shell quenches the photoluminescence intensity of the ZnO nanocrystals by about 72%, primarily due to charge transfer reactions and static quenching. A red shift in the absorption peak is also observed. Under the solar simulated spectrum (AM1.5G), we report enhanced power conversion efficiency (35%) with higher short current circuit (80%) for lead sulfide-based solar cells as compared to devices prepared by pristine ZnO nanocrysals. Furthermore, a simple and novel method was used to synthesize a new structure of graphene which can be called hollow graphene. First, the ZnO-Graphene QDs synthesized by solution method and then ZnO QDs were dissolved from this structure using an acidic solution to obtain hollow structure of graphene. Afterward, this structure was used in PbS QDs solar cell in order to improve the transport of electron and decrease the recombination of the carriers. A power conversion efficiency of 5.3% was obtained using hollow graphene as a fast electron extraction layer due to the enhancement of EQE and current density. Finally, we fabricated the PbS QDs on nanotube structure in order to improve the light absorption and carriers collection. A PCE of 4.3% (20% improvement) was attained using this structure. In addition, we employed anti-reflection layer to enhance the absorption and utilize self-cleaning properties of this layer on top of PbS QDs device
  9. Keywords:
  10. Lead Sulfide ; Graphene ; Simulation ; Solar Cells ; Photovoltaic Cell ; Band Gap ; Colloidal Quantum Dots

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