Synthesis and Characterization of Dithiafulvalene and 2,1,3-Benzothiadiazole-based D-A Conjugated Polymers and Their Applications in Polymer Solar Cells

• Main Authors: Cheng-Chieh Huang, 黃正傑
• Other Authors: Po-Chih Yang
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/se4fj6

碩士 === 元智大學 === 化學工程與材料科學學系 === 102 === Recently, organic photovoltaic cells (OPVs) based on bulk hetero-junction (BHJ) between an electron rich π conjugated polymer donor and an electron deficient fullerene-based acceptor have attracted considerable attention for applications in renewable energy, because of their advantages of having low cost and easy fabrication, being lightweight, and having the capability to fabricate flexible large-area devices. For increasing power conversion efficiency (PCE) of the PSCs, great efforts have been devoted to the design and synthesis of new conjugated polymer donor and new fullerene derivative acceptor photovoltaic materials. It has been realized that an ideal polymer donor in OPVs should exhibit broad with high absorption coefficient in the visible region and an energy level suitable for a fullerene acceptor to form a nanoscale bicontinuous interpenetrating network. To date, the design and synthesis of donor-acceptor (D-A) copolymers has been proven to be one of the most successful strategies to satisfy the above requirements. A series of well-defined D-A or D-π-A conjugated alternating polymers, incorporating dithiafulvalene-based monomers as electron donor unit and 2,1,3-benzothiadiazole-based monomers as electron acceptor unit, were synthesized through Suzuki and Yamamoto coupling polymerizations. This D-A approach and the using DTF for designing the polymers is highly effective for tuning band gap and energy levels by choosing a suitable combination from the vast variety of donor units and acceptor units available. The intra-molecular charge transfer (ICT) between the donor and acceptor units may effectively reduce the band-gap energies of the resulting polymers. The synthesized polymers have glass transition temperatures ranging from 131.7 to 151.3 oC. The onset weight-loss temperatures of the polymers are in the range of 211.3 to 432.2 oC. Substitution with 2,1,3-benzothiadiazole groups produced bathochromic shifts to visible region in the absorption spectra of PFBT, PFTBT, PFDTBT, and PFTDTBT. We report on the improved power conversion efficiencies (PCEs) approaching 1.78 % for BHJ polymer solar cells based on P3HT/PCBM system by doping 5 wt % of a novel dithiafulvalene-based D-A oligomer, PTBT. Open-circuit voltage (Voc), short-circuit current (Jsc), and fill factor (FF) are 0.57 V, 6.08 mA/cm2, and 51.3 %, respectively. Different weight ratios of doping PTBT in P3HT/PCBM system are applied and the performances of the resulting solar cells are compared. Introducing 2 wt % PTBT causes a significant increase of the charge-carrier mobility from 2.01 #westeur024# 10-4 to 4.59 #westeur024# 10-4 cm2 V-1 S-1. The higher solar cell performances are attributed to the improved miscibility and the better mobility of the charge carriers of the dithiafulvalene with P3HT/PCBM, leading to a significant enhancement of PCE and an effective charge-transporting phase.