Synthesis, Properties and Photovoltaic Applications of Conjugated Polymer Containing Benzothiadiazole and Difluorothiophene

• Main Authors: Rong-Xian Jhang, 張容銜
• Other Authors: Shan-hui Hsu
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/hnr4jv

碩士 === 國立臺灣大學 === 高分子科學與工程學研究所 === 107 === The introduction of fluorine atom on the backbone of conjugated D-A polymers is a common approach to improve the photovoltaic properties of polymer solar cells due to down-shifted HOMO and LUMO levels, enhanced light absorption, improved backbone coplanarity, increased carrier mobilities and suppressed recombination. In this work, a new donor-acceptor structured conjugated polymer, BT3T-2F, is synthesized by coupling benzothiadiazole acceptor block with terthiophene donor block, in which the middle thiophene unit is 3,4-difluorothiophene. Compared with 3,3’-difluoro-2,2’-bithiophene, the 3,4-difluorothiophene has advantages of simple synthesis route and low cost. Moreover, the two fluorine atoms can interact with S and/or H on both neighbor units, forming a coplanar three-member block. For comparison, an analog without fluorine atoms, BT3T-2H, is also prepared. Experimental results from photoelectron spectroscopy, UV-vis spectroscopy, X-ray diffraction and space charge limited current measurements indicate the replacement of the middle thiophene in the terthiophene with 3,4-difluorothiophene results in deeper HOMO and LUMO levels, enhanced absorption coefficient in solid film, better crystallinity and higher hole mobility, respectively. Consequently, the bulk heterojunction solar cells based on BT3T-2F:PC61BM exhibited a promising power conversion efficiency (PCE) of 6.91 % with a Voc of 0.81 V, a Jsc of 12.50 mA and an FF of 68.55 %, while the BT3T-2H:PC61BM cell has a PCE of 3.74 % with a Voc of 0.73 V, a Jsc of 8.02 mA and an FF of 63.5 %.