The Design, Synthesis And Applications Of Novel Conjugated Polymers Containing Alkyl Triazole For Polymer Solar Cells

With the development of the industrialization of human society, it is a growing importantissue for searching the new energy for the replacement of the traditional resources, such ascoal, petroleum and natural gas. Among variety of the new energy, the use of solar energy canbe traced back to ancient times due to its inexhaustible feature. Compared with the inorganicsilicon-based solar cells, the organic polymer solar cells (PSCs) have attracted tremendousattention due to its characteristics such as light weight, low toxic, low cost, flexible andportable. Despite the Power conversion efficiency of the PSC had exceeded10%, there is stilla lot of work to do for their commercialization. At present, two major factors should berefined in PSC, one is the low efficiency, and the other is the lifetime.The research of the photodetectors (PDs) possesses huge significance in terms ofindustry, military affairs and scientific instruments. As a very important subdiscipline, theorganic near-infrared (NIR) photodetectors own lower cost, higher detectivity and broaderabsorption spectrum compared with the inorganic PDs. However, the research of PDs isrelatively few compared with PSCs in recent years. It is an important issue to design andchoose narrow bandgap polymers with broader photoresponse.This thesis’s research refers to two system: on one hand, we concluded the pastachievements on benzothiadiazole and alkalized benzotriazole, and design the conception ofcombining two electron-deficient group：thiadiazole and triazole onto the same benzene ringfor the stronger acceptor:6-(2-alkyl)-[1,2,5]thiadiazole[3,4,-f]benzotriazole, and combinedthis monomer with different donor to form D-A narrow bandgap copolymers in theapplication of PSCs and PDs. On another hand, we started from the precursor ofnaphtothiadiazole, which is a successful case in the PSC, and synthesized a novel monomer asthe acceptor: naphtho[1,2-c:5,6-c]bis(2-octyl-[1,2,3]triazole)(TZNT). The TZNT-basedcopolymers demonstrated excellent results when used in the PSC.In the second chapter, we discussed the design principle and synthesis route of6-(2-alkyl)-[1,2,5]thiadiazole[3,4-f]benzotriazole in details, and copolymerized the monomerwith the weak donor: fluorene and carbazole, via Suzuki copolymerization. The obtainedproducts owned ideal absorption spectra and bandgap, one of which obtained the PCE exceeding3%.In the third chapter, we copolymerized the6-(2-alkyl)-[1,2,5]thiadiazole[3,4,-f]benzotriazole with the stronger donor--benzo[1,2-b:4,5-b’]dithiophene. A series of copolymers with narrow bandgaps were obtainedand one of which was characterized in details. The absorption edge of polymers based on6-(2-alkyl)-[1,2,5]thiadiazole[3,4,-f]benzotriazole had exceeded1100nm, and the detectivitycould also be comparable to the inorganic-based photodetectors. The stability of the devicedwas enhanced when the MoO3was applied in the structure,85%photoresponse strengthcould be maintained after exposure in the air for15days.In the fourth chapter, we discussed the advantages of naphthothiadiazole, and drawed theconclusion that naphthalene had better planarity than benzene, then we pointed out that thelow solubility of naphthothiadiazole was the main drawback. Therefore, we designed a novelacceptor and brought the alkalized benzotriazole into the structure. The acceptor isnaphtho[1,2-c:5,6-c]bis(2-octyl-[1,2,3]triazole). In this chapter, we focused on the design andsynthesis route of this monomer, and synthesized thenaphtho[1,2-c:5,6-c]bis(2-octyl-[1,2,3]triazole)-based D-A copolymers for the first time.Compared with benzotriazole-based copolymer, the former owned better photovoltaic result,which demonstrated the naphtho[1,2-c:5,6-c]bis(2-octyl-[1,2,3]triazole) could be applied inthe PSC.In the fifth chapter, based on the polymer in the last chapter, we continued to do somemodification on the molecular structures of the polymers. We enhanced the conjugated lengthvia the linkage of thiophene bridges, and enhanced the solubility of the copolymers via thelinkage of bulk alkyl side chains. There of the copolymers with similar structures weresynthesized, one of which demonstrated high PCE exceeding6%with traditional structure,and further enhancement of PCE could reach7%when the polymer was applied in theinverted structure. The high performance among the copolymers with large bandgap is not socommon, which could be comparable with P3HT as a type of classical materials. This resultsshowcased the potential of the naphtho[1,2-c:5,6-c]bis(2-octyl-[1,2,3]triazole)-basedcopolymers in the PSCs. In the sixth chapter, we copolymerized the monomer with stronger D part in the hope offorming D-A conjugated polymers with narrower bandgaps and broader absorption spectra.We found the characterizations were in line with our expectation and we believed that as anovel acceptor used in the copolymers, thenaphtho[1,2-c:5,6-c]bis(2-octyl-[1,2,3]triazole)-based copolymers would have bright future inthe application of active layer of PSCs.