Synthesis And Properties Of Water/Alcohol-soluble Organic Optoelectronic Materials And Acceptor-pended Conjugated Polymers

Semiconducting conjugated polymers and small molecules have attracted growingattentions due to their great application potentials in optoelectronic devices such as solar cellsand light-emitting diodes over the past decades. Among them, water/alcohol-soluble organicconjugated materials have exhibited wide applications owing to their excellent optoelectronicproperties, unique solubility and outstanding interfacial modification functions. On the otherhand, organic/polymer solar cells (OPVs) have also gained much attentions due to their lowcost and compatibility with large-scale processing. The power conversion efficiencies ofOPVs have approached to the commercialization threshold mainly benefiting from thedevelopment of new conjugated polymer donors.The studies demonstrated in this thesis include two parts. The first part is thedevelopment of new water/alcohol soluble conjugated organic materials and the explorationof their new applications, which can overcome the shortcomings of traditional water/alcoholsoluble conjugated polymers. The second part is the development of a new high-performanceconjugated polymer family for use as donors in OPVs, which are different from theextensively studied linear conjugated polymers.In chapter2, a series of zwitterionic conjugated polyelectrolytes were developed withthe aim at overcoming the negative influences caused by the mobile counterions in traditionalconjugated polyelectrolytes and the limited solubility of neutral water/alcohol solubleconjugated polymers. The introduction of zwitterionic groups not only endowed the resultingpolymers with excellent solubility in polar solvents but also suppressed the movement of ions.It was found that zwitterionic conjugated polyelectrolytes is superior to tradition conjugatedpolyelectrolytes when used as interfacial modification layer in polymer light-emitting diodes(PLEDs) and OPVs. The effects of chemical structures of conjugated main chains on theinterfacial modification properties of water/alcohol conjugated polymers. It was revealed thatthe energy alignment between interfacial layer and active layer is a key factor that determinedthe interfacial modification abilities of water/alcohol soluble conjugated polymers. Thisdiscovery provided a guideline to design new interfacial materials and optoelectronic devices. In chapter3, a phosphate group-containing alcohol soluble fullerene derivative wasdeveloped to apply as modifier for indium tin oxide (ITO) in inverted OPVs. It was foundthat this fullerene derivative can lead to the decrease of work function of ITO significantly,and consequently enhance the electron collection in ITO electrode and improve the powerconversion efficiency of OPVs by30%. This study suggested that water/alcohol solublefullerene derivatives which combined ideal energy levels, excellent electron collectingabilities and unique solubilities are very promising interfacial materials for OPVs.In chapter4, an alcohol-soluble narrow-band gap conjugated polymer and a fullerenederivative which were functionalized with amino-group were developed towardenvironmentally-friendly solvents processed OPVs. Despite positive expects, the blendsystem was not able to lead to any output of photocurrent when they were incorporated intoOPVs as active layer. However, both of them performed well as electron-collecting layer inOPVs. In-depth studies revealed the hole-trap nature of aliphatic amine and the complexationbetween amine and fullerene, which suppressed the photocurrent output when they werepresence in active layer. On the other hand, the n-doping of fullerene by aliphatic amine andthe accumulation of hole traps adjacent to metal electrode are beneficial to the deviceperformances. The studies in this chapter are very important to develop new materials forenvironmentally-friendly processed OPVs in the future and to understand the workingmechanisms of water/alcohol soluble interfacial materials.In chapter5, a serious of acceptor-pended D-A conjugated polymers, which differedfrom extensively studied linear conjugated polymers were developed for use as donors inOPVs. Acceptor-pended conjugated polymers have a lot of advantages, such as facilities forcontrolling absorption spectra, band gap and energy level by simple chemical modification,better isotropic charge transport properties and better solubilities. A large family ofconjugated polymers was developed by combining the advantages of acceptor-pendedmolecular design and several promising building blocks (such as silicafluorene, carbazole andindenofluorene). The absorption spectra, band gaps and energy levels were finely tuned byattaching different acceptor groups (such as malononitrile,1,3-diethylthiobarbituric acid,2-(1,2-dihydro-1-oxoinden-3-ylidene)) onto the end of the conjugated side chains of the polymers, and by enhancing the concentration of D-π-A chromophores and changing thealkyl side chains. Moreover, two conjugated polymers whose absorption spectra covered thewhole visible light region and even extended into infrared light region were developed byconstructing two different D-π-A chromophores on one polymer chain, which provided a newapproach to extend the absorption spectra for conjugated polymers. All of theacceptor-pended conjugated polymers exhibited moderate performance as donors in OPVswith high open-circuit voltage and highest power conversion efficiency of4.47%. The studiesin these chapters developed a new system of donor materials for OPVs.