Synthesis and photovoltaic properties of benzo[1,2-b:4,5-b′]dithiophene derivative-based polymers with deep HOMO levels
作者:Heung Gyu Kim、Sae Byeok Jo、Chiyeoung Shim、Jaewon Lee、Jisoo Shin、Eun Chul Cho、Soo-Ghang Ihn、Yeong Suk Choi、Yungi Kim、Kilwon Cho
DOI:10.1039/c2jm32514d
日期:——
Two benzo[1,2-b:4,5-bâ²]dithiophene (BDT) derivatives with conjugated substituents, triisopropylsilylethynyl (TIPS) and 4-octylphenylethynyl groups, were synthesized as donor units (D) and copolymerized with two acceptor units (A), 4,7-bis(4-octylthiophen-2-yl)-2,1,3-benzothiadiazole (BT) and 4,4â²-diundecyl-2,2â²-bithiazole (BTZ), respectively, using Stille coupling reaction to afford four new copolymers, PTBDT-BT, PTBDT-BTZ, POPEBDT-BT, POPEBDT-BTZ. All polymers exhibited highest occupied molecular orbital (HOMO) energy levels that were deeper than â5.4 eV due to the conjugated substituents. Small band gaps were successfully achieved for PTBDT-BT (1.67 eV) and POPEBDT-BT (1.67 eV) and were attributable to the strong intramolecular charge transfer within the DâA alternating structure. The resultant photovoltaic performances showed high open-circuit voltages (Voc) ranging from 0.73 V to 0.92 V, whereas the power conversion efficiencies (PCEs) depended strongly on the blend morphologies. The polymer solar cell based on the blend of PTBDT-BT and PC71BM gave the best photovoltaic performance among the series, with a high Voc of 0.81 V and a PCE of 4.61%.
合成了两种带有共轭取代基(三异丙基硅乙炔基和4-辛基苯乙炔基)的苯并[1,2-b:4,5-b']二噻吩(BDT)衍生物作为给体单元(D),并分别与两种受体单元(A),即4,7-双(4-辛基噻吩-2-基)-2,1,3-苯并噻二唑(BT)和4,4'-二十一烷基-2,2'-双噻唑(BTZ),通过Stille偶联反应共聚,得到四种新型共聚物,即PTBDT-BT、PTBDT-BTZ、POPEBDT-BT和POPEBDT-BTZ。所有聚合物均表现出高于-5.4 eV的最高占据分子轨道(HOMO)能级,这是由于共轭取代基的影响。PTBDT-BT(1.67 eV)和POPEBDT-BT(1.67 eV)成功实现了小带隙,这可归因于D-A交替结构中强烈的分子内电荷转移。由此得到的光伏性能显示,开路电压(Voc)在0.73 V至0.92 V之间,而功率转换效率(PCE)则强烈依赖于混合形态。基于PTBDT-BT和PC71BM混合物的聚合物太阳能电池在该系列中表现出最佳的光伏性能,具有0.81 V的高Voc和4.61%的PCE。