利用聚苯胺/多層奈米碳管/石墨烯複合材料製作染料敏化太陽能電池對電極之製程及性能研究

Abstract

本論文主要是以聚苯胺、多層奈米碳管和石墨烯複合薄膜取代白金薄膜作為染料敏化太陽能電池對電極之催化層。首先，以苯胺硫酸鹽酸性溶液作為有效分散劑避免石墨烯與多層奈米碳管彼此堆疊與聚集。再分別利用定電位電化學聚合法與化學氧化/定電位電化學聚合法分別於FTO玻璃與載玻片表面形成複合薄膜。由四點探針與TGA分析結果，添加石墨烯與多層奈米碳管之複合薄膜表面電阻下降與熱重量損失下降量減少，證實利用定電位電化學聚合法與化學氧化/定電位電化學聚合法可成功地製備出PANi/Graphene/MWCNTs複合薄膜。 實驗第一部分:以定電位電化學聚合法於FTO玻璃表面形成PANi薄膜，其光電轉換效率為5.55±0.05 %。當添加石墨烯與多層奈米碳管適當的含量比例(苯胺/石墨烯=1/0.0045；苯胺/多層奈米碳管=1:0.0045)時，光電轉換效率分別提升至7.29±0.08% 與 7.21±0.08% .。以苯胺/石墨烯/多層奈米碳管的重量比例為1/0.0030/0.0045所製備出的PANi/Graphene/MWCNTs複合薄膜，達到最佳的光電轉換效率7.67±0.05%。此外，添加石墨烯與多層奈米碳管可使得短路電流由15.48 mA/cm2提升至18.21 mA/cm2。 實驗第二部分:以化學氧化/定電位電化學聚合法於載玻片表面形成PANi薄膜，其光電轉換效率為0.58±0.02%。當添加石墨烯與多層奈米碳管適當的含量比例(苯胺/石墨烯=1/0.0060；苯胺/多層奈米碳管=1:0.0060)時，光電轉換效率分別提升至2.04±0.08% 與 2.03±0.07%。以苯胺/石墨烯/多層奈米碳管的重量比例為1/0.0045/0.0060所製備出的PANi/Graphene/MWCNTs複合薄膜，達到最佳的光電轉換效率3.58±0.06% 。此外，添加石墨烯與多層奈米碳管可使得短路電流由3.64±0.06mA/cm2提升至9.38±0.07 mA/cm2. 由循環伏安法分析結果可得知，PANi/Graphene/MWCNTs複合薄膜相較於PANi、PANi/Graphene與PANi/MWCNTs而言，I3－於其表面還原成 I－之催化活性能力較佳，主要原因歸因於PANi/Graphene/MWCNTs複合薄導電性較佳而提升表面還原電流密度，使得短路電流、光電轉換效率與電量收集效率提升。另一方面，光電轉換分析中，以PANi/Graphene/MWCNTs複合薄膜當作對電極，其開路電壓值較大，主要與循環伏安法所測得的還原電位較高有關。

This paper is mainly concerned with the replacement of platinum with polyaniline (PANi), graphene and multi-walled carbon nanotube (MWCNT) composite films used as a catalysis layer in counter electrode of dye-sensitized solar cells (DSSC). First, we used aniline sulfate solution as an efficient dispersing agent to debundle MWCNTs and to avoid graphenes aggregated. The composite films were grown on fluorine-doped tin oxide (FTO) and glass substrates by using electro-chemical deposition and chemical/electro-chemical deposition respectively. From the results of four-point probe and thermo-gravimetric analysis, the surface resistance and the weight loss percentage of the films were decreased with the addition of graphenes and MWCNTs. Accordingly, the PANi/Graphene/MWCNTs composite films were successfully fabricated by electro-chemical deposition and chemical/electro-chemical deposition. In the first part of this research, the PANi film were grown on the FTO-coated glass as counter electrodes of DSSCs by using electro-chemical deposition. The power conversion efficiency of as-fabricated DSSC was 5.55±0.05 % .When adding the proper amount of graphenes and MWCNTs (aniline/graphene=1/0.0045；aniline/MWCNTs=1/0.0045 ) , the power conversion efficiency were raised to 7.29±0.08% and 7.21±0.08% . The highest power conversion efficiency was 7.67±0.05%, when the weight ratio of aniline/graphene/MWCNT was 1/0.0030/0.0045. In addition , the addition of graphene and MWCNTs could enhance the Jsc of DSSC from 15.48 to 18.21 mA/cm2. In the second part of this research, the PANi film was grown on the glass slide as a counter electrode of DSSC by using chemical/electro-chemical deposition. The highest power conversion efficiency of as-fabricated DSSC was 0.58±0.02%. When adding the proper amount of graphenes and MWCNTs (aniline/graphene=1/0.0060；aniline/graphene=1/0.0060) , the power conversion efficiency were raised to 2.04±0.08% and 2.03±0.07%. The highest power conversion efficiency was 3.58±0.06%, when the weight ratio of aniline/graphene/MWCNTs was 1/0.0045/0.0060. In addition , the addition of graphene and MWCNTs could enhance the Jsc of DSSC from 3.64±0.06 to 9.38±0.07 mA/cm2. From the result of cyclic voltammetry (CV) analysis, the PANi/Graphene, PANi/MWCNTs, and PANi/Graphene/MWCNTs composite films compared to neat PANi have higher catalysis of converting tri-iodide (I3－) to iodide (I－) due to their higher conductivity and higher redox current density. The increase of redox current density resulted in higher Jsc, higher power conversion efficiency, and better charge collection efficiency of DSSCs. In addition, the open-circuit voltage of DSSCs was higher with the PANi/Graphene/MWCNTs counter electrode because of the higher reduction potential for I－/ I3－ redox couples.