以「苯二噻吩」剛硬片段為共軛架橋之有機光敏染料與高效能染敏太陽能電池

Abstract

利用引入hexyl 或3,5-bis(hexyloxy)benzyl取代基之剛硬片段BDTD (benzo[1,2-b:6,5-b']dithiophene-4,5-dione)，以及不同的芳香雜環片段(thiophene、4,4-dihexyl-4H-cyclopenta[1,2-b:5,4-b']dithiophene、dithieno[3',2':3,4;2'',3'':5,6]benzo[1,2- d][1,2,3]triazole)作為雙極性非金屬系有機光敏染料之共軛架橋，以三苯胺作為電子與體、2-cyanoacrylic acid作為電子受體兼錨基，本研究成功開發出新穎的非金屬光敏化染料 (LBS系列染料)。本研究也對染料進行了光物理、電化學性質測量，以及製成染料敏化型太陽能電池進行測試，並搭配理論計算探討元件表現與染料分子之關聯性。 LBS系列染料在416 nm到497 nm的光譜範圍有寬廣的吸收，且擁有不錯的消光係數，最高的消光係數達到~50900 M-1 cm-1。此外，延伸共軛長度可使染料吸光範圍紅位移。由於BDTD的共面性，染料分子在TiO2上有相當程度的J-型堆疊，使得分子的吸收延伸至較長的波段。在標準AM 1.5光照度下，LBS系列元件之光電轉換效率為3.93%−8.38%，最佳的LBS-4 (8.38%)已超過標準品N719元件(8.12%)。從IPCE光譜可以很清楚看出J-型堆疊對於光電流的增益有很重要的貢獻，若加入5 mM的共吸附劑 (CDCA) 適度抑制堆疊導致的激態分子淬息，但保存長波段的光吸收，可將效率更提升至9.11%。 New metal-free dipolar sensitizers (LBS dyes) with a rigid segment containing hexyl or 3,5-bis(hexyloxy)benzyl substituents, benzo[1,2-b:6,5-b']dithiophene-4,5-dione (BDTD), and heteroaromatic segment such as thiophene, 4,4-dihexyl-4H-cyclopenta[1,2- b:5,4-b']dithiophene or dithieno[3',2':3,4;2'',3'':5,6]benzo[1,2-d][1,2,3]triazole as the π-conjugated spacer, triarylamine as the donor, and 2-cyanoacrylic acid as both the acceptor and anchor, have been synthesized and characterized. The photophysical and electrochemical properties were also carried out on these new dyes. Dye-sensitized solar cells (DSSCs) were fabricated using these dyes as the sensitizers, and relevant physical measurements were conducted. Theoretical computations were also used to correlate the cell performance with the molecular structure. The LBS sensitizers display broad absorption spectra covering the range of 416 to 497 nm, with the highest molar extinction coefficient up to ~50,900 M-1cm-1. Elongation of the conjugated spacer results in red shift of the asbsorption. The planarity nature of BDTD results in J-aggregation of the dyes on the TiO2 surface and extends the absorption to the longer wavelength region. The light-to-electricity conversion efficiencies of DSSCs fabricated range from 3.93 to 8.38% under simulated AM 1.5 G illumination, and the best cell efficiency (LBS-4) surpasses that (8.12%) of the standard DSSC based on N719 ((bis(tetrabutyl-ammonium)-cis-di(thiocyanato)-N,N'-bis(4-carboxylato-4'-carboxylic acid -2,2'-bipyridine)ruthenium(II)). The IPCE spectra clearly indicate that important contribution of J-aggregation of the dyes to the photocurrents. With addition of 5 mM of CDCA (chenodeoxycholic acid) as the coadsorbent to alleviate excited state quenching while retaining the gain at the longer wavelength region due to dye-aggregation, the best efficinecy was further boosted to 9.11%.