以寡噻吩為中心引入不同長度的烷基側鏈之小分子應 用於異質接面太陽能電池

Abstract

在本研究中，我們以 Oligothiophene ( 寡噻吩 ) 作為主鏈合成一系列小分子受體-供體-受體 （A-D-A） 的結構，以具有良好吸光性的 Thiobarbituric acid ( TB ) 雜環作為電子受體，且在他們的中央單位引入不同長度的烷基側鏈形成 TB3tBT 系列 ( TB3tBT-H 、 TB3tBT -C4 、 TB3tBT-C8 、 TB3tBT-C12 ) 之小分子，並將這些化合物的結構 - 性能關係進行了研究分析且應用於 Bulk Heterojunction （ BHJ ）太陽能電池元件。我們發現引入不同長度的烷基側鏈對於小分子材料之熱性質、、吸光特性、分子間堆疊能力以及元件特性皆有所影響。 為了更進一步探討小分子於薄膜中的結晶排列情形，我們進行二維之 GI-WAXS ( grazing-incidence wide-angle X-ray diffraction ) 薄膜繞射測定。 TB3tBT-H 分子作用力較強，退火後具有較強的結晶特性，經由混摻 PC61BM 製成元件後發現 TB3tBT-H 和TB3tBT -C 8 比TB3tBT-C4 和TB3tBT-C12 有更高的光電轉換效率（ PCE ）。採用 GI-WAXS ( grazing-incidence wide-angle X-ray diffraction ) 探測小分子材料在主動層中 packing 的情形，我們發現了小分子的堆疊的方式對所述Bulk Heterojunction （ BHJ ）太陽能電池元件的光電特性有很大的影響，特別是對開路電壓（ VOC ）的值。

In this study we synthesized a series of solution-processable small molecules based on the configuration of acceptor-donor-acceptor (A－D－A), but with alkyl side chains of different lengths presented from their central units ( TB3tBT-H 、 TB3tBT-C4 、 TB3tBT-C8 、TB3tBT-C12 ). Then the structure–property relationships of these compounds were investigated in terms of their packing behaviors and bulk heterojunction (BHJ) photovoltaic properties, and we found that the packing of these molecules in neat films is critically dependent of their side chain architectures, as evidenced by the variations in their lamellar structures determined with grazing-incidence wide-angle X-ray diffraction. The photovoltaic characteristics of these small molecules when combined with fullerenes in BHJ devices exhibited zigzag-shaped variations relative to their side chain length, with the power conversion efficiencies (PCEs) of devices incorporating TB3tBT-H and TB3tBT-C8 being higher than those of devices incorporating TB3tBT-C4 and TB3tBT-C12. Using grazing-incidence wide-angle X-ray scattering to probe the molecular packing in the active layers, we found that the ways of stacking of the small molecules had a great impact on the photovoltaic performances of the bulk heterojunction devices incorporating them, especially for the values of open circuit voltage (VOC), with the devices comprising small molecules displaying greater degrees of interdigitation providing the highest values of VOC.