Tuning optical and electronic properties of star-shaped conjugated molecules with enlarged π-delocalization for organic solar cell application
作者:Youyu Jiang、Di Yu、Luhua Lu、Chun Zhan、Di Wu、Wei You、Zhizhong Xie、Shengqiang Xiao
DOI:10.1039/c3ta11001j
日期:——
Three structurally related conjugated molecules (BTT-BTD-0, BTT-BTD-1 and BTT-BTD-2) in star shape have been designed and synthesized as donor materials for small molecule based bulk heterojunction (BHJ) solar cells. The structural features of these molecules include a planarized benzo[1,2-b:3,4-bâ²:5,6-bâ³]trithiophene (BTT) with a C3h symmetry as the central core and three conjugated arms incorporating electron deficient benzo[2,1,3]thiadiazole (BTD) units, with arms being linked to the core via different number of thiophene connecting units (e.g., 0, 1, 2 corresponding to BTT-BTD-0, BTT-BTD-1 and BTT-BTD-2, respectively). Comparative analyses of optical and electronic properties indicate that the molecules bearing more thiophene units between the BTT core and the BTD arms possess higher-lying HOMO levels while their LUMO levels remain almost unchanged. The improvement of BHJ device performance, with [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) as the acceptor, is observed with increasing number of thiophene units between the BTT core and BTD arms, from BTT-BTD-0 to BTT-BTD-1 and BTT-BTD-2. The BTT-BTD-2:PC61BM based BHJ devices show the highest power conversion efficiency (PCE) of 0.74%, with an open-circuit voltage (Voc) of 0.69 V, a short-circuit current density (Jsc) of 2.93 mA cmâ2, and a fill factor (FF) of 0.37 under 1 sun (100 mW cmâ2) AM 1.5G simulated solar illumination. The PV performance of BTT-BTD-2 is further improved when [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) is used as the electron acceptor, yielding the best device performance with Jsc of 4.13 mA cmâ2, Voc of 0.72 V, FF at 0.46 and PCE of 1.36%. The effect of the different number of thiophenes linking the BTT core and the conjugated BTD arms has been clearly demonstrated on regulating optical and electrochemical properties of the three molecules and their BHJ device performances.
我们设计并合成了三种结构相关的星形共轭分子(BTT-BTD-0、BTT-BTD-1 和 BTT-BTD-2),作为基于小分子的体异质结(BHJ)太阳能电池的供体材料。这些分子的结构特征包括:以 C3h 对称的平面化苯并[1,2-b:3,4-bâ²:5,6-bâ³]三噻吩(BTT)为中心核,以及包含缺电子苯并[2,1,3]噻二唑(BTD)单元的三个共轭臂、0、1、2 分别对应 BTT-BTD-0、BTT-BTD-1 和 BTT-BTD-2)。光学和电子特性的比较分析表明,在 BTT 核心和 BTD 支臂之间含有更多噻吩单元的分子具有更高的 HOMO 水平,而其 LUMO 水平几乎保持不变。以[6,6]-苯基-C61-丁酸甲酯(PC61BM)为受体的 BHJ 器件性能随着 BTT 核心和 BTD 臂之间噻吩单元数量的增加而提高,从 BTT-BTD-0 到 BTT-BTD-1 和 BTT-BTD-2。基于 BTT-BTD-2:PC61BM 的 BHJ 器件的功率转换效率(PCE)最高,达到 0.74%,开路电压(Voc)为 0.69 V,短路电流密度(Jsc)为 2.93 mA cmâ2,在 1 个太阳(100 mW cmâ2)AM 1.5G 模拟太阳光照射下的填充因子(FF)为 0.37。当使用[6,6]-苯基-C71-丁酸甲酯(PC71BM)作为电子受体时,BTT-BTD-2 的光伏性能得到进一步提高,器件性能最佳,Jsc 为 4.13 mA cmâ2,Voc 为 0.72 V,FF 为 0.46,PCE 为 1.36%。连接 BTT 核和共轭 BTD 臂的噻吩数量不同对调节这三种分子的光学和电化学性质及其 BHJ 器件性能的影响已经得到了清楚的证明。