Synthesis and Characterization of π-Conjugated Copolymers Containing 4，4’-Bisalkyl-3，3’-Dicyano-2，2’-Bithiophene Electron Acceptor and their Application for Organic Photovoltaics

• Main Authors: Chun-Wen Kan, 甘竣文
• Other Authors: 鄭如忠
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/16607369872715967682

碩士 === 國立臺灣大學 === 高分子科學與工程學研究所 === 101 === We have synthesized and characterized aseries ofnew-conjugateddonor-acceptor (D-A) copolymers (PBTCNOc-T,PBTCNOc-2T,PBTCNOc-TT,PBTCNHx-DTTT and PBTCNOc-DTTT) bearing dicyanobithiophene unit(BTCN) as the electron acceptorwith various thiophene-based unit as the electron donorvia Stille coupling reaction. The electron donors of these copolymers arethiophene (T),2，2’-bithiophene (2T),thieno-[3,2-b]thiophene (TT) and3, 6-dioctyl-2, 5-di(thiophen-2-yl)thieno[3, 2-b]thienothiophene (DTTT),respectively. The electron donor, DTTT can be considered as a hybrid form of 2T and TT, and the two n-octyl side chains on the thienothiophene unit provide the sufficient solubility of PBTCNHx-DTTT and PBTCNOc-DTTT necessary for the solution fabricationof organic photovoltaics. Experiment evidences indicate that different electron donor moiety affects the stacking of the copolymers and hence their energy levels.A pronounced red-shifted UV-visible absorption band was observed for the thin films sample of PBTCNHx-DTTT and PBTCNOc-DTTT when compared with that of solution samples. This is attributed to the appropriate location and distribution of the alkyl side chains that affects the main chain stacking of these copolymers. All copolymers studied herein containing cyano (CN) substituents, strong withdrawing functional groups. The HOMO energy levelof these copolymers are all deepened IV compared with that of poly(3-hexyl)thiophene (P3HT). Such deepened HOMO energy level are beneficial to the increasing open-circuit voltage (VOC) of the device. The power conversion efficiency (PCE) of inverted bulk-heterojunction organic photovoltaics(OPVs)based on ITO/ZnO/PBTCNOc-DTTT:PC61BM (w/w= 1:1)/MoO3/Agis2.74%. AVOCof 0.82V,short-circuit currentdensity (Jsc)of 6.97 mA/cm2, and fill factor (FF) of0.48,have been achieved. Aninvertedbulk-heterojunction OPVs based on ITO/ZnO/ P3HT:PC61BM ( w/w = 1:1)/MoO3/Ag wasalsofabricated tocomparewith aforementioned device of PBTCNOc-DTTT. It has a PCE of 3.68%, a VOCof 0.57V, Jsc of 11.17 mA/cm2, and (FF) of 0.58.