Synthesis and Characterization of Cross-shaped Benzodithiophene and Disk-liked Benzotrithiophene Small Molecules for the Application in Organic Solar Cells
|關鍵字:||有機薄膜太陽能電池;十字型小分子;organic thin film solar cells;cross-shaped small molecule|
本研究第一部份成功合成以苯并雙噻吩 (benzodithiophene, BDT) 為中心電子予體，上下左右接上三噻吩基團 (terthiophene) 作為共軛側鍊，外端接上3-ethylrhodanine作為電子受體之十字型小分子DR3TBDT3T，其UV吸收峰落在400 nm至700 nm之廣範圍，電化學能隙值在1.8 eV。將此小分子材料與PC71BM混摻之後，應用於混摻異質接面型太陽能電池之主動層上，以DIO作為添加劑，能有效改善混摻情形，得到之光電轉換效率為2.52 % (Voc = 0.84 V, Jsc = 6.71 mA cm-2, FF = 44.7 %)。以穿透式電子顯微鏡 (TEM) 觀察在主動層之型態，可看出與文獻參考值不太相同，因構型不同而影響與PC71BM混摻情形，未達到預期之光電轉換效率。
本研究第二部分成功合成出以苯并三噻吩 (benzotrithiophene, BTT) 為主體，外端接上一個噻吩 (thiophene) 與氰乙酸異辛酯 (2-ethylhexyl cyanoacetate) 作為電子受體之三角形盤狀小分子結構TCTBTT，因共軛長度不足，UV吸收峰範圍最高只到約莫576 nm，能隙值高於2 eV。將此小分子材料與PC61BM混摻之後，應用於混摻異質接面型太陽能電池之主動層上，因成膜性不佳，得到之光電轉換效率為0.02 % (Voc = 0.74 V, Jsc = 0.08 mA cm-2, FF = 35.5 %)。|
The goal of this study is aimed to synthesis the cross-shaped molecule and disk-liked molecule for the application in organic solar cells (OPV). In addition, we discuss their crystallinity. In the first part of this study, the cross-shaped small molecule named DR3TBDT3T with a benzo[1,2-b:4,5-b’]dithiophene (BDT) unit as the central building block, the terthiophene unit as the conjugated linking group, and the 3-ethylrhodanine unit as the electron-acceptor have been designed and synthesized. It’s UV absorption peaks is at the range from 400-700 nm and band gap is around 1.8 eV. This small molecule was used to fabricate the bulk heterojunction OPV devices using PC71BM as an acceptor. We used DIO as the additive to improve the morphology and the device performance. The DR3TBDT3T/PC71BM based device exhibited the power conversion effiency (PCE) of 2.52 %. (Voc = 0.84 V, Jsc = 6.71 mA cm-2, FF = 44.7 %) When we used transmission electron microscopy (TEM) to analyze the morphology of the blend film in the active layer, we could find that it was very different with the reference data, and the device performance is not as high as we expected. In the second part of this study, a disk-liked small molecule named TCTBTT with a benzo[1,2-b:3,4-b’:5,6-b’’]trithiophene (BTT) as the central building block, three conjugated arms incorporating one thiophene and 2-ethylhexyl cyanoacetate as the electron-acceptor have been designed and synthesized. Due to its short conjugated length, its UV absorption does not appear strong red-shiftand and band gap is more than 2 eV. This small molecule was used to fabricate the bulk heterojunction OPV devices using PC61BM as an acceptor. Due to its poor film forming quality, the TCTBTT/PC71BM based device exhibited the power conversion effiency (PCE) of 0.02 % (Voc = 0.74 V, Jsc = 0.08 mA cm-2, FF = 35.5 %).