新穎施體-受體聚噻吩系共軛高分子衍生物之合成及有機太陽能電池應用

Abstract

高分子太陽能電池由於其價格低廉，可利用溶液態時以捲式塗佈技術進行大面積加工，且於應用上具可撓性，使這項研究近幾年來受到極大重視。目前由P3HT/PCBM混成系統做成的太陽能電池元件效率為4%，為了製備效率超越P3HT/PCBM混成的太陽能電池元件，尋找一具備適當能階的低能隙高分子便成一重要課題。低能隙高分子對太陽光譜中可見光至近紅外光區段有較廣的吸收因而能有效提升太陽能元件之效率。在本篇碩士論文中，藉由Suzuki連結聚合法成功合成出施體與受體交替式之高分子PF-co-DMOTB及PC-co-DMOTB，合成之兩種高分子對一般溶劑具良好的溶解性，UV吸收光譜亦可發現其對可見光有良好的吸收。電化學及光學上測量判斷其能隙與能階，PF-co-DMOTB 其能隙為1.90eV ，PC-co-DMOTB則為1.82eV，其低能隙及施體受體交替之特性使其對光譜有較廣之吸收。由循環伏安法測量高分子HOMO之能階， PF-co-DMOTB為-5.19eV ，PC-co-DMOTB為-5.70eV，均低於P3HT之HOMO能階，此項優點使其製成元件時能形成較高之開路電壓。塊材異質接面型太陽能電池製做時將高分子與碳材PCBM混掺做主動層，導電玻璃 ITO為陽極，上層鋁金屬為陰極，實驗結果顯示，製備太陽能電池之最佳效率為由高分子PF-co-DMOTB與PCBM混掺比例為1：4時而得，各項參數如下：開路電壓Voc=0.69 eV，短路電流Jsc=1.06 mA cm-2 ，填充系數FF=0.25，及元件效率0.18%，此結果於太陽光模擬器A.M.1.5強度為100 mW cm-2下測得。

Polymer solar cells (PSCs) have attracted stong interest in recent years due to the prospect of low cost, solution-based processing and the capability to fabricate flexible devices. To further enhance the power conversion efficiency of 4% achieved from solar cells made of regioregular poly(3-hexylthiophene)/[6,6]-phenyl-C61-butyric acid methyl ester (P3HT/PCBM), a low band gap conjugated polymers with proper energy levels for charge transfer are required. Low optical bandgap conjugated polymers may improve the efficency of organic photovoltaic devices by increasing the absorption in the visible and near infrared region of the solar spectrum. In this master thesis work, I synthesized two new highly soluble and strongly visible-light absorbing alternating polymers using Suzuki coupling polymerization method that are based on 4,7-Bis-(3,4-dimethoxy-thiophen-2-yl)-benzo[1,2,5]thiadiazole monomers: poly[2,7-(9,9-dihexylfluoren)-alt-5,5-(4,7-Bis-(3,4-dimethoxy-thiophen-2-yl)-benzo[1,2,5]thiadiazole] (PF-co-DMOTB) and poly[9-eicosyl-3,6-carbazole-alt-5,5-(4,7-Bis- (3,4-dimethoxy-thiophen-2-yl)-benzo[1,2,5]thiadiazole](PC-co-DMOTB). Electrochemical and photophysical studies reveal band gaps of 1.90eV for PF-co-DMOTB and 1.82eV for PC-co-DMOTB, which could effectively harvest broader solar spectrum. The cyclic voltammetry measurements show that the HOMO level of the polymers are -5.19eV for PF-co-DMOTB and -5.70eV for PC-co-DMOTB which are significantly lower than that of P3HT. Bulk heterojuncion photovoltaic devices were fabricated using blends of these copolymers with PCBM as the active layer, ITO-glass as the anode, and aluminum as the cathode. It is observed that the best performing solar cell device which made from polymer PF-co-DMOTB (80 wt% PCBM) delivers an open circuit voltage Voc=0.69 eV, Jsc=1.06 mA cm-2 , FF=0.25 and power conversion efficiency 0.18% under an illumination of A.M.1.5 with an intensity of 100 mW cm-2.