應用於染料敏化太陽能電池新穎釕錯合物染料之合成與元件光電性質研究

Abstract

論文的主要目的在於研發新穎的釕錯合物分子，以應用於染料敏化太陽能電池。我們採用一鍋化方式合成一系列含有電洞傳輸材料carbazole、phenothiazine及benzothiophene官能基的釕金屬錯合物，[Ru(dcbpy)(L)(NCS)2]，其中dcbpy為4,4’-dicarboxylic acid-2,2’bipyridine，L分別為4,4’-Bis[(E)-2-(N-ethylcarbazole-3-yl)vinyl]-2,2’-bipyridine (SW1)、4,4’-Bis[(E)-2-(N-hexylcarbazole-3-yl)vinyl]2,2’-bipyridine (SW2)、4,4’-Bis{(E)-2-[N-(4-hexyloxyphenyl)carbazole-3-yl]vinyl}2,2’-bipyridine (SW3)、4,4’-Bis- {(E)-2-[(N-hexylcarbazol-3-yl)thiophen-5-yl]vinyl}2,2’-bipyridine (SW4)、4,4’-Bis[(E)-2-(N-ethylphenothiazin-3-yl)vinyl]2,2'-bipyridine (SW5)及4,4'-Bis-[(E)-2-(benzo[b]thiophene-3-yl)vinyl]2,2'-bipyridine (SW6)。所有的錯合物皆在純化後經由 NMR、MASS、EA 等鑑定方法進行結構分析與純度探討，並藉由UV-Vis及Emission光譜，配合氧化還原電位測量而計算出每個染料分子之HOMO與LUMO能階。經由吸收光譜的分析可知，加入carbazole、phenothiazine以及benzothiophene衍生物將有助於延伸配位基的共軛長度，增強吸光係數進而達到增加太陽光的收集能力(light-harvesting ability)。 我們將合成好的釕金屬錯合物吸附在TiO2奈米粒薄膜當作陽極，I-/I3-當作電解液而製備成染料敏化太陽能電池元件，並在AM1.5太陽模擬光源照射下進行光電轉換效能的測量。我們發現SW1的光電轉換效率可達7.41 %，而SW2及SW3中含有hydrophobic group有助於降低傳輸中的電子與氧化態電解液I3-再結合的機率而增加VOC，並可降低水氣所造成的元件損壞，增加元件的長時穩定性。由TiO2厚度測試可知此系列的錯合物具高吸光係數的特性，適用於較薄的TiO2層，在主動層厚度7.65 □m即可達最高電流密度，未來它們將可應用於固態元件。我們的研究結果顯示，加入共軛環thiophene (SW4)與phenyl (SW6) 有助於延伸光譜吸收但卻會降低溶解度，影響染料吸附量而降低光電轉換效率。此外，加入不同的電洞傳輸材料 (SW5)，可以有效增加電荷分離的效果，而使VOC增高。 另一方面，我們合成了文獻上已發表過的對稱結構HRS-12與Z907作為對照組，來研究已發表過之不對稱結構HRS-9與尚未發表的不對稱結構Z907-1。經由光電轉換效率及交流阻抗分析測量，我們發現不對稱結構的染料吸附量遠較對稱結構高，但是對於含有雜環分子 (HRS-9)的染料，電子在傳輸過程中由於分子間的堆疊損失掉，降低JSC，對於具有疏水官能基德分子 (Z907-1)，JSC提高但阻絕電解液I3-的能力較低VOC下降，整體元件效能差異則不大。

Novel Ruthenium complexes (SW dyes), which contain the carbazole, phenothiazine or benzothiophene as a secondary electron donor moiety, were designed and synthesized for dye-sensitized solar cell (DSSC) applications. The general formula for the target sensitizes is expressed as [Ru(dcbpy)(L)(NCS)2] where dcbpy represents 4,4’-dicarboxylic acid-2,2’-bipyridine and L represents 4,4’-bis[(E)-2-(N-ethylcarbazole-3-yl)-vinyl]2,2’-bipy- ridine (SW1), 4,4’-bis[(E)-2-(N-hexylcarbazole-3-yl)vinyl]2,2’-bipyridine (SW2), 4,4’-bis- {(E)-2-[N-(4-hexyloxyphenyl)carbazole-3-yl]vinyl}2,2’-bipyridine (SW3), 4,4’-Bis{(E)-2- [(N-hexylcarbazol-3-yl)thiophen-5-yl]-vinyl}2,2’-bipyridine (SW4), 4,4’-Bis-[(E)-2-(N- ethylphenothiazin-3-yl)vinyl]2,2’-bipyridine (SW5), or 4,4'-Bis-[(E)-2-(benzo[b]thiophene-3-yl)vinyl]2,2'-bipyridine (SW6). These complexes were synthesized via a typical one-pot procedure and identified with NMR, EA and Mass measurements. The corresponding DSSC devices were characterized based on steady-state spectral, IV/IPCE, and CV/EIS measurements. The design of SW1 containing the carbazole group extends the conjugation of the bipyridine ancillary ligand and increases remarkably the absorption coefficient for the improved light-harvesting ability. This spectral feature enables us to fabricate a new generation DSSC device with a much thinner TiO2 film (7.6 □m). In addition, we have designed two dyes (SW2, SW3) with a structure similar to SW1 but containing hydrophobic groups to retard the electron interception with I3- and increase the stability of the devices. Moreover, we found that the new dyes (SW4, SW6) with increased conjugation length would extend the absorption spectra toward longer wavelengths, but at the same time they suffered poor solubility to give the low amounts of dye loading. Finally, the ligand with another hole transport functional group was designed to make a new Ru dye (SW5) with increased charge separation to enhance the VOC. Among these new Ru dyes, the best device performance results from SW1, which gives power conversion efficiency ~7 %. In addition, we synthesized the known dye HRS-12 and Z907 with symmetric ancillary ligand. Furthermore, we also synthesized the known dye HRS-9 and the novel dye Z907-1 [Ru(dcbpy)(4-methyl-4’-nonyl-2,2’-bipyridine)(NCS)2] with asymmetric ancillary ligand. We find that the asymmetric dyes improve JSC than the symmetric dyes due to higher dye-loading. In the other case, dyes with heterocyclic group (HRS-9) may induce energy loss in the electron transfer process due to the intermolecular aggregation result in decreasing JSC.