Synthesis And Optoelectronic Properties Of Low Bandgap Conjugated Polymers Based On Indolo[3,2-b] Carbazole

Polymer solar cells (PSCs) have attracted both academic and industrial interests in recent years because of their particular advantages in terms of light-weight, mechanical flexibility as well as low-cost fabrication of large-area devices. Typically, PSC bulk heterojunction architectures comprise a blend of an electron-donating narrow band-gap conjugated polymer (donor) and an electron-accepting fullerene derivative (acceptor).D-A low band-gap conjugated polymers have excellent thermostability, numerous variety, adjustable structure and flexible manufacturing, which make them become the research emphasis in the donor materials used in polymer solar cells. In principle, the ideal donor conjugated polymers should have narrow band-gap along with absorbance well-matched with solar spectrum, low-lying highest occupied molecular orbital (HOMO) energy levels that can offer high open-circuit voltage, excellent ambient stability, high charge carrier mobility that can allow for the effective diffusion or drift of the generated holes and electrons to electrodes, as well as good solubility for device fabrication.Indolo[3,2-b]carbazole (ICz) owns fused rigid conjugated plane structure and the generated copolymers show excellent thermal stabilities, relatively deep highest occupied molecular orbital energy level (EGOMO), as well as decent charge carrier transport properties due to the extended conjugation length by the fused aromatic structures. An additional priority of ICz is that it can be facilely synthesized with flexible structural modification at different positions. The two nitrogen atoms may allow for alkylation which can impart polymers superior solubilities to the carbazole counterparts.In chapter2, a series of conjugated polymer donor materials PICz-BTZ, PICz-TBTZ, PICz-EBTZ based on indolo[3,2-b]carbazole and benzotriazole were synthesized by Suzuki polymerization. Polymer solar cells based on the copolymers were fabricated with the configuration of ITO/PEDOT:PSS/Polymer:PCBM/PFN/A1. The highest power conversion efficiency (PCE) was achieved based on device with PICz-TBTZ:PC71BM (1:3, wt:wt) as photoactive layer, with PCE of4.9%and short-circuit current(JSC), open-circuit voltage (VOC) and fill factor (FF) of5.45mAcm-2, 0.95V and68.8%, respectively, which is the highest PCE in polymer solar cells with polymers based on indolo[3,2-b]carbazole as the donor material.In chapter3, polymer donor materials PICz-TC8TzTz, PICz-TC12TzTz based on indolo[3,2-b]carbazole and thiazolo[5,4-d]thiazole were synthesized by Suzuki polymerization. The space charge limited current mobility measurements showed a hole mobility of21×10-5cm-V-1S-1and1.57×10-4cm-2S-1for polymer PICz-TC8TzTz and polymer PICz-TC12TzTz. Polymer solar cells based on the copolymers were fabricated with the configuration of ITO/PEDOT:PSS/Polymer:PC71BM/PFN/Al. The Voc, Jsc, FF, PCE of the polymer solar cell based on polymer PICz-TC12TzTz were0.68V,2.21mAcm-2,29.4%,0.64%, while the device performance based on polymer PICz-TC8TzTz were0.73V,2.41mAcm-2,56.3%,0.99%.