聚三己基噻吩混掺二氧化鈦奈米桿有機太陽能電池之光電性質的研究

Study on photocurrent properties of organic hybrid solar cell based on poly(3-hexylthiophene) and TiO2 nanorods

羅喜興(Hsi-Hsing Lo)

指導教授 ： 林唯芳

共同指導教授 ： 陳俊維

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.01664

摘要

聚噻吩（polythiophene）及二氧化鈦，由於其具有較好的化學穩定性、熱穩定性及優良的電荷傳導能力，而常應用於有機太陽能電池中的電子予體及電子受體材料。於本論文之研究，主要是在探討如何有效改善聚三己基噻吩(poly(3-hexylthiophene), P3HT)與二氧化鈦奈米桿(TiO2 nanorods)混掺型的有機太陽能電池效率。由於有機太陽能電池的效率主要決定於材料吸收光源的量、激子分離以及電荷傳輸等因素，因此我們藉由研究高分子以及無機奈米材料的基礎特性；包括二氧化鈦奈米桿於混掺中的含量、吸附於二氧化鈦奈米桿表面的界面活性劑種類、導電層的厚度、高分子的分子量以及高分子所使用的溶劑，以有效改善激子分離及電荷傳輸，進而提升電池的效率。

於研究混掺比例以及導電層膜厚中，我們藉由所製備的元件效率得出最佳化的混掺比例以及導電層的最佳厚度分別為：w P3HT/w TiO2 nanorods = 47/53與125 nm。我們也探討高分子的分子量以及其所使用的溶劑對於元件效率的影響，因高分子的分子量大小或是所使用的溶劑差異皆有可能使高分子成膜厚度及其構形上有所改變，影響激子分離以及電荷傳輸的效率，進而影響元件效率。在這部分的研究結果指出，當聚三己基噻吩的分子量越大且所使用的溶劑為氯苯時，聚三己基噻吩於成膜後的構形上有較共平面的結構，使得高分子鏈與鏈之間的π-π堆疊程度較好，進而提升電荷傳輸的效率。於研究界面活性劑的效應方面，我們試著導入具有導電性的界面活性劑於二氧化鈦奈米桿的表面，因為在混掺後聚三己基噻吩與二氧化鈦奈米桿之間有界面活性劑的存在，因此界面活性劑的導電能力將影響到分離後的電荷是否能夠有效傳輸至電極。在此部分，我們將已吸附於二氧化鈦奈米桿表面的界面活性劑置換成具有導電性質的分子，且有效改善激子的分離以及電荷傳輸的能力，使得元件效率有進一步的提升。

若將上述所探討的各個影響電池效率的因素之最佳化參數合併在一起並且利用此製程參數製備聚三己基噻吩混掺二氧化鈦的有機太陽能電池(參數為：P3HT的分子量為66kD、溶劑為氯苯、二氧化鈦奈米桿的表面吸附著Pyr、混掺組成：w P3HT/w TiO2 nanorods = 47/53且導電層的膜厚調控在120~130 nm)，目前效率於A.M. 1.5照光下已可達到約0.7 ％。

關鍵字

聚三己基噻吩 ； 二氧化鈦奈米桿 ； 混掺比例 ； 膜厚 ； 溶劑 ； 高分子的分子量 ； 界面活性劑 ； 有機太陽能電池

並列摘要

Polymer-based solar cell has been fabricated by blending the conjugated polymer, poly (3-hexylthiophene) (P3HT) with TiO2 nanorods. Polythiophene and titania are frequently used as good electron donor and electron acceptor in organic solar cells, respectively, due to their good chemical stability, thermal stability and excellent charge transport properties. In our study, we tried to improve the power conversion efficiency of P3HT/TiO2 nanorods hybrid organic solar cell. Because device’s efficiency is determined by light harvesting, exciton dissociation and charge transport, so we tried to improve the efficiency of exciton dissociation and charge transport by studying the fundamental properties of active layer made from a solution consisted of conducting polymer and inorganic nanocrystal hybrid material. The effect of material properties on the photocurrent include hybrid composition, film thickness, polymer molecular weight, solvent type and ligand type.

For the influence of hybrid composition and active layer thickness on the device efficiency, the results showed that the device has better performance at 53 % by weight of TiO2 nanorods and at about 125 nm film thickness. For the effect of polymer molecular weight and solvent type in the hybrid on the device efficiency, we have found a high molecular weight polymer (~66 kD) and a medium volatile solvent of chlorobenzene provide best materials for high efficiency cell. The efficiency of exciton dissociation and charge transport in the device also can improve by surface modification of inorganic nanocrystal. We used pyridine, thienyl phosphonic acid and thienyl carboxylic acid to exchange oleic acid that capped on the surface of TiO2 nanorods. The results show the hybrid materials made of surface modified TiO2 nanorods exhibit better performance as compared to that of end-capped by oleic acid due to the improved surface interaction between polymer and nanocrystals.

The best performance devices was fabricated from a blend ratio of 47 to 53 by weight in P3HT to TiO2 nanorods, a film thickness of about 125 nm, chlorobenzene as a solvent, a P3HT molecular weight of 66kD, pyridine as a surfactant. The device exhibits power conversion efficiency, 0.7% under air mass 1.5 simulated solar illumination (100 mW/cm2).

並列關鍵字

poly (3-hexylthiophene) ； TiO2 nanorods ； hybrid ratio ； active layer ； thickness ； solvent ； molecular weight ； ligand ； organic solar cell

參考文獻

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