Syntheses of functional materials for organic photovoltaic and electrochromic device applications

Varlıoğlu, Figen
Thienothiophene based moities are widely investigated for organic solar cell applications. In this study, after synthesizing 2-ethylhexyl 4,6-dibromothieno [3,4-b]thiophene-2-carboxylate successfully, copolymerization with commercially available donor 4-(2-ethylhexyl)-2,6-bis(trimethylstannyl)-4H-dithieno[3,2-b:2',3'-d]pyrrole, DTPy, was performed via Stille coupling. At each step, Nuclear Magnetic Resonance (NMR) Spectroscopy were performed for structural analysis. Cyclic voltammogram was used for investigation of electrochemical behaviors. Oxidation potentials of the polymer were monitored at 0.25 V/ 0.81 V for p-doping and 0.08 V/ 0.52 V for p-dedoping. Moreover, spectroelectrochemical analysis was done in order to obtain λmax value which was determined to be 728 nm. Optical band gap was calculated to be 1.2 eV. This clearly shows that a strong NIR absorbing polymer was successfully synthesized. Kinetic studies show optical contrast of PTTDTPy is 14 % at 1055 nm and 17% at 720 nm with 1.43 at 1055 nm and 0.9 at 720 nm switching times. The performance of the polymer in organic solar cells is currently being investigated. In the field of conjugated polymer systems, PEDOT has a special place. PEDOT and its derivatives are used in a variety of applications, spanning from electrochromic devices to bulk-heterojunction solar cells. Even though there is an immense interest surrounding this family of compounds the long pursued symmetric bifunctional derivative PDiEDOT (poly-dithieno[3,4-b:3',4'-e][1,4]dioxine and ProSOT (poly-3,4-dihydro-2H-thieno[3,4-b]oxathiephine) have not been realized. An eight step synthesis was envisioned in this study for realization of DiEDOT. Seven steps of this synthesis were successfully completed. Future studies will be concerned with finalization of the synthesis and investigation of electrochemical and electrochromic properties. The novel corresponding monomer of ProSOT was successfully synthesized for the first time in this study. However the monomer was not electrochemically active. Hence this monomer was brominated and moiety was coupled with stannylated 3,4-ethylenedioxythiophene EDOT to realize a novel electroactive monomer. For structural analysis NMR spectroscopy and HRMS were used. Electrochemical polymerization was performed with cyclic voltammogram with 0.1 DCM/ACN/NaClO4/LiClO4 systems. Oxidation potentials of the polymer was detected at 0.26 V for p-doping and 0.04 V for p-dedoping. Spectroelectrochemical results reveal that λmax values were 515 nm and 555 nm and optical band gap of the polymer was calculated as 1.60 eV. Moreover, kinetic studies were conducted. At 515 nm, optical contrast of corresponding polymer was founded as 49% fast switching time of 0.8 seconds. This optical contrast value is superior to the corresponding homopolymer of EDOT, PEDOT.
Citation Formats
F. Varlıoğlu, “Syntheses of functional materials for organic photovoltaic and electrochromic device applications,” M.S. - Master of Science, Middle East Technical University, 2017.