Synthesis And Properties Of Organic Optoelectronic Materials Based On Indacenodiselenophenes

Organic photovoltaic (OPV) solar cells are an extremely active area of research,in order to meet the urgent need for clean and renewable sources of energy. Duringthe last decade the field of organic photovoltaics has shown a continuousimprovement in both device efficiency and understanding of the underlying physicalfundamentals. Despite exhibiting lower power conversion efficiency (PCE) incomparison to conventional inorganic counterparts, organic photovoltaic cells haveattracted particular attention due to their potential applications with flexiblity,low-cost and solution processiblity. More and more new conjugated polymers weresythesized to enhance the solar spectrum absorption and PCE. Most of donorpolymers have a wide band gap, and unmatched energey level with acceptors leadingto low short circuit current and PCE. Therefore, low band gap polymers haveattracted more and more interest in OPV area. In recent years, PCE close to10%havebeen achieved based on low band gap polymers and [6,6]-phenyl-C71-butyric acidmethyl ester (PC71BM). Most of those highly-efficient low band gap polymerscontain thiophene unit. As Se in the same group with S, selenophene and thiophenehave similar chemical properties. The polarizability of the lone pair electrons inselenophene is stronger, which cause stronger interaction between Se-Se inselenophene based polymers. Therefore, polymers based on selenophene have beganto be studied extensively. In this thesis, the research on the synthesis, characterizationand properties of selenophene based low band gap polymers P1, P2and P3has beencarried out as following.1. Low band gap polymers of P1, P2and P3were successfully sythesized byStille cross-coupling reaction with indacenodiselenophene (IDSe) as electron donorunit and benzo[c][1,2,5]thiadiazole and its derivatives as electron acceptor unit. Theyposseseed0,2,4thiophene rings in the electron acceptor unit respectively. Thechemical structure of intermediate products, target monomers and polymers wereidentified by1H NMR,13C NMR and mass spectrometry or GPC.2. P1, P2and P3possesed good solubility in common organic solvents such astoluene, chlorobenzene, chloroform, and good thermal stability as well with5% weight loss around300oC. The optical properties of polymer P1, P2and P3weremeasured by UV-vis spectroscopy.Their optical band gaps were1.66eV,1.77eV and1.80eV, respectively. A strong absorption peak of P1located between600~800nm.With the number of thiophene units increasing, P2and P3shown better absorptionaround500nm. P1and P3exhibited complementary absorption in the visible lightregion. The more thiophene rings in the electron acceptor unit, the weaker electronacceptor ability, the higher LUMO level of the corresponding polymer. The LUMOlevel of P1was located at-3.51eV, P2was0.06eV higher than P1, and P3was0.02eV higher than P2.3. BHJ solar cells were prepared respectively with the three polymers andelectron acceptor PC71BM. The ratio of the donor and acceptor materials, solventadditives and modified materials of electrode were investigated. P1shown high shortcurrent density above12mA/cm2, and the optimal PCE reached4.3%. P3shown highVoc about0.85V, and also with a good photovoltaic performance about3.3%.