Design And Sythesis Of Novel Donor-Acceptor Conjugated Polymers For Organic Photovoltaic Solar Cells

Organic photovoltaic (OPV) solar cells have their own advantages: light weight, flexibleand their performance can be easily modified through modification of material chemicalstructure. As a special kind of organic material, polymer materials have all theabove-mentioned advantages; and at the same, polymer materials have their own uniqueadvantage: solution processibility. Ink-jet printing and spin coating are two typicalsolution processing technologies. It is easily to fabricate large-area devices with low costwhen solution processing technologies are used. Therefore, this advantage of polymermaterials makes them especially attractive in industry. Many different kind of newpolymer materials are synthesized and used as efficient semiconducting materials in OPVdevices. It is an active research area that concerning the design and synthesis of newmonomer and corresponding low-band-gap conjugated polymers. The goal is to buildpolymer materials with adequate absorption and electrochemical properties so that theycan be used as efficient semiconducting materials in OPV devices; and at the same time, itis important to investigate the chemical structure-device performance relationshipsthrough this kind of research effort. It is also the work of my graduate research. Myresearch is summarized as below, and it is the content of this dissertation as well:1. In chapter2, we designed and synthesized a new monomer, pyromellitic diimides(BDI), and three BDI based conjugated polymers, PTBDI，PTTBDI and PBBDI, weresynthesized. Their absorption properties and electrochemical properties are characterized.Unfortunately, none of the three polymers were used as efficient semiconducting materialsin semiconducting devices. Nevertheless, the optical and electrochemical properties of thenew polymers were compared with those of their NDI and BDI analogues. This kind ofcomparison helped us to understand the properties of polymers with this similar diimidesstructure better. The research in this chapter is helpful for design of new chemical structures in the future.2. In chapter3, a pentalene derivative was synthesized and used as building block inconjugated polymers. It is the first time that a pentalene containing unit wascopolymerized to build conjugated copolymers. Two new conjugated copolymers weresynthesized and their absorption properties, electrochemical properties were characterizedand compared. The semiconducting properties of the two new polymers were investigatedin semiconducting devices, but the result was negative. Nevertheless, it investigated a newunit in building conjugated copolymers, and further modification of the chemical structuremight help to build efficient new polymer materials in the future.3. In chapter4, we investigated a new building block, di(2-furyl)thiazolo[5,4-d]thia-zole (DFTT). Two new conjugated D-A copolymers, PBDTODFTT and PBDTTDFTT,were synthesized using DFTT as the electron-deficient unit, and using alkoxyl groupsubstituted benzo[1,2-b:4,5-b’]dithiophene (BDTO) and thiophenyl group substitutedbenzo[1,2-b:4,5-b’]dithiophene (BDTT) as the electron-rich unit, respectively. Theirabsorption properties, electrochemical properties and the performance of correspondingdevices were characterized and compared. The best power conversion efficiency (PCE) ofcorresponding devices were1.87%and3.07%for PBDTODFTT and PBDTTDFTT,respectively.4. In chapter5, we designed and synthesized a pair of isomers: benzo[1,2-b:5,4-b’]difuran (syn-BDF) and benzo[1,2-b:4,5-b’]difuran (anti-BDF). Using syn-BDF andanti-BDF as electron-rich units, D-A copolymers were synthesized: syn-PBDFDPT andanti-PBDFDPT. Their electron-deficient units were dioxopyrrolothiophene (DPT).anti-PBDFDPT is insoluble in common solvent. The absorption properties,electrochemical properties and the performance of corresponding devices ofsyn-PBDFDPT were characterized. The best power conversion efficiency (PCE) ofcorresponding devices was only0.021%for syn-PBDFDPT. Based on this, wecopolymerized both syn-BDF and anti-BDF with isoindigo unit to build two new D-A conjugated copolymers: syn-PBDFID and anti-PBDFID. The use of isoindigo unitsuccessfully lengthened the absorption wavelength of the new copolymers. Theirabsorption properties, electrochemical properties and the performance of correspondingdevices were characterized and compared. The best power conversion efficiency (PCE) ofcorresponding devices were1.44%and0.65%for syn-PBDFID and anti-PBDFID,respectively.