Enhanced Photovoltaic Performance in D-π-A Copolymers Containing Triisopropylsilylethynyl-Substituted Dithienobenzodithiophene by Modulating the Electron-Deficient Units

Junfeng Tong; Lili An; Jie Lv; Pengzhi Guo; Xunchang Wang; Chunyan Yang; Yangjun Xia

doi:10.3390/polym11010012

Enhanced Photovoltaic Performance in D-π-A Copolymers Containing Triisopropylsilylethynyl-Substituted Dithienobenzodithiophene by Modulating the Electron-Deficient Units

Polymers (Basel). 2018 Dec 21;11(1):12. doi: 10.3390/polym11010012.

Authors

Junfeng Tong¹, Lili An², Jie Lv³, Pengzhi Guo⁴, Xunchang Wang⁵, Chunyan Yang⁶, Yangjun Xia⁷

Affiliations

¹ School of Materials Science and Engineering, Lanzhou Jiaotong University, Lanzhou 730070, China. tongjunfeng139@163.com.
² School of Chemical Engineering, Northwest Minzu University, Lanzhou 730030, China. anlili2011@163.com.
³ School of Materials Science and Engineering, Lanzhou Jiaotong University, Lanzhou 730070, China. zoeyejie@163.com.
⁴ National Green Coating Technology and Equipment Research Center, Lanzhou Jiaotong University, Lanzhou 730070, China. shxygpz@126.com.
⁵ CAS Key Laboratory of Bio-Based Materials, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, China. wang_xc@qibebt.ac.cn.
⁶ School of Materials Science and Engineering, Lanzhou Jiaotong University, Lanzhou 730070, China. YChY-5@126.com.
⁷ School of Materials Science and Engineering, Lanzhou Jiaotong University, Lanzhou 730070, China. xiayangjun2015@126.com.

Abstract

Three alternated D-π-A type 5,10-bis(triisopropylsilylethynyl)dithieno[2,3-d:2',3'-d']-benzo[1,2-b:4,5-b']dithiophene (DTBDT-TIPS)-based semiconducting conjugated copolymers (CPs), PDTBDT-TIPS-DTBT-OD, PDTBDT-TIPS-DTFBT-OD, and PDTBDT-TIPS-DTNT-OD, bearing different A units, including benzothiadiazole (BT), 5,6-difluorinated-BT (FBT) and naphtho[1,2-c:5,6-c']-bis[1,2,5]thiadiazole (NT), were designed and synthesized to investigate the impact of the variation in electron-deficient units on the properties of these photovoltaic polymers. It was exhibited that the down-shifted highest occupied molecular orbital energy level (E_HOMO), the enhanced aggregation in both the chlorobenzene solution and the solid film, as well as the better molecular planarity, were achieved using methods involving fluorination and the replacement of BT with NT on the polymer backbone. The absorption profile was little changed upon fluorination; however, it was greatly broadened during replacement of BT with NT. Consequently, the optimized photovoltaic device based on the PDTBDT-TIPS-DTNT-OD exhibited synchronous enhancements in the open-circuit voltage (V_OC) of 0.88 V, the short-circuit current density (J_SC) of 7.21 mA cm^-2, and the fill factor (FF) of 52.99%, resulting in a drastic elevation in the PCE by 129% to 3.37% compared to that of the PDTBDT-TIPS-DTBT-OD. This was triggered by PDTBDT-TIPS-DTNT-OD's broadened absorption, deepened E_HOMO, improved coplanarity, and enhanced SCLC mobility (which increased 3.9 times), as well as a favorable morphology of the active layer. Unfortunately, the corresponding PCE deteriorated after incorporating fluorine into the BT, due to the oversized aggregation and large phase separation morphology in the blend films, severely impairing its J_SC. Our preliminary results demonstrated that the replacement of BT with NT in a D-π-A type polymer backbone was an effective strategy of tuning the molecular structure to achieve highly efficient polymer solar cells (PSCs).

Keywords: TIPS-substituted dithienobenzodithiophene; fluorination; modulating the electron-deficient units; naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole; photovoltaic property.