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DTSTAMP:20260524T000036Z
DESCRIPTION: \n\nAbstract\n\nThis research thesis focuses on two main studi
 es involving micro/nano structural engineering of organic/inorganic semico
 nductor devices for development of next generation high performance and st
 able electronics. In the first project\, we have explored the potential of
  GaN-based nanocrystals for the development of artificial photosynthesis d
 evices for the conversion of CO2 to syngas\, a mixture of CO and H2\, and 
 one of the promising future solar fuels. By integrating the Pt/TiO2 cocata
 lyst with the strong light harvesting of p-n Si junction and efficient ele
 ctron extraction effect of GaN nanowires\, we demonstrated an efficient an
 d stable photoelectrochemical (PEC) reduction of CO2 into syngas product w
 ith controlled composition. It was found that the metal/oxide interface pr
 ovides multifunctional catalytic sites that are inaccessible with the indi
 vidual components\, which structurally and electronically facilitate CO2 c
 onversion into CO. As a result\, a record solar-to-syngas (STS) efficiency
  of 0.87 % and a benchmark turnover number (TON) of 24800 are achieved. In
  addition\, we developed a decoupling strategy involving Au-Pt dual cocata
 lysts to achieve high energy conversion efficiency with controlled syngas 
 composition. By integrating spatially separated a CO-generating catalyst (
 Au) and an H2-generating catalyst (Pt) with GaN nanowires on planar Si pho
 tocathode\, we achieved a record photon-to-current efficiency of 1.88 % an
 d controllable syngas product with tunable CO/H2 ratio (0–10) under one-su
 n illumination. Our designed PEC system exhibited highly stable syngas pro
 duction in the 10 h duration test.\n\n \n\nIn the second project we invest
 igated the improvement of organic field-effect transistors (OFETs) perform
 ance and stability using doping strategy. OFETs are emerging as promising 
 building blocks for large-area printable and flexible electronics. However
 \, they have yet to be implemented in practical applications due to operat
 ional challenges such as low mobility and device instability\, both of whi
 ch are linked to charge carrier trapping phenomena. Intentional molecular 
 doping has been found to be an effective approach for mitigating trap stat
 es and enhancing the charge transport. However\, unresolved issues such as
  unwanted off current and limited library of applicable molecular dopants 
 have limited the effectiveness of the doping technique in addressing OFETs
  operational challenge. Here\, we have introduced nitrofluorene (NF) accep
 tors as novel p-dopants for polymer OFETs due to superior solubility\, air
  stability\, and ease of energy level tunability. The addition of NFs to a
  standard commercial DPP-DTT polymer showed outstanding device performance
 \, including an ∼5-fold enhancement in the saturation field-effect mobilit
 y (up to ∼8 cm2V−1 s −1)\, lowering threshold voltage\, and one order of m
 agnitude decrease in contact resistance. The NF-doping mechanism was inves
 tigated via spectroscopic\, microscopic\, and electrical characterization\
 , which revealed the synergetic effect of filling deep traps and modified 
 microstructure on significantly improved performance OFETs. In continue\, 
 we evaluated the environmental and operational stability of pristine and d
 oped transistors. By exploring the impact of air exposure on pristine OFET
  performance\, we found that suppression of electron-induced traps by oxyg
 en doping\, as well as diffusion of water molecules to semiconductor netwo
 rks\, lead to device environmental instability. We demonstrate that TeNF d
 oping suppresses both effects\, resulting in environmentally independent p
 erformance and good long-term stability of unencapsulated devices in ambie
 nt air (10% deterioration after 4 months storage). The doped OFETs also sh
 ow significantly reduced bias stress effect and hysteresis. Such improveme
 nt of the environmental and operational stabilities is achieved by suppres
 sing the majority-carrier traps (including electron-induced deep traps)\, 
 and better microstructural order in TeNF doped polymer films.\n
DTSTART:20221205T183000Z
DTEND:20221205T183000Z
LOCATION:\, Room 603\, McConnell Engineering Building\, CA\, QC\, Montreal\
 , H3A 0E9\, 3480 rue University
SUMMARY:PhD defence of Pegah Ghamari - Development of Next Generation Photo
 electrochemical and Polymer Transistor Devices
URL:/ece/channels/event/phd-defence-pegah-ghamari-deve
 lopment-next-generation-photoelectrochemical-and-polymer-transistor-343959
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