混摻導電高分子/二氧化鈦奈米桿太陽能電池

Hybrid Solar Cells Based on Conjugated Polymers and TiO2 Nanorods

曾琮瑋(Tsung-Wei Zeng)

指導教授 ： 林唯芳

國立臺灣大學/工學院/材料科學與工程學研究所/博士(2009年)

https://doi.org/10.6342/NTU.2009.01546

摘要

巨異質接面高分子太陽能電池由電子給體與受體的互穿網狀混合物構成，例如：共軛高分子混摻碳六十，共軛高分子混摻高分子，共軛高分子混摻無機奈米顆粒等等，已可以達到相當高的光電轉換效率。二氧化鈦奈米顆粒是一種環保材料，基於其優異物理與化學穩定性，具備高度潛力作為高分子太陽能電池的組成材料。二氧化鈦奈米顆粒可以在高分子太陽能電池中增加電荷分離，作為電子受體與電子傳導路徑。於文獻中，二氧化鈦奈米顆粒可應用於製作高分子太陽能電池已經被提出，共軛高分子混摻二氧化鈦奈米顆粒太陽能電池具備諸多優點。然而，共軛高分子混摻二氧化鈦奈米桿太陽能電池則尚未曾被製作並且評估效率。
本研究中，我們發掘將二氧化鈦奈米桿運用於共軛高分子混摻無機奈米顆粒太陽能電池的潛力。一維方向的奈米桿可以提供直線方向電荷傳導，因此適用於建構有效的電荷傳導網絡於巨異質接面高分子太陽能電池。
於第一部分研究中，巨異質接面光伏元件由聚〔2-甲氧基-5-(2'-乙基-己氧基)-1,4-苯乙烯〕與二氧化鈦奈米桿混摻材料製備。我們提出於元件中的光作用層與鋁電極之間插入一層二氧化鈦奈米桿。二氧化鈦奈米桿層可以作為電子傳導與電洞阻擋層，導致短路電流密度增為2.5倍。於565nm的單光照射下，能量轉換效率為2.2%，外部量子效率於430nm最大可以達到24%。於A.M. 1.5 模擬太陽光照下，轉換效率為0.5%。
於第二部分的研究，一種高電洞遷移率共軛高分子，聚(3-己烷噻吩)，與二氧化鈦奈米桿被用於建構高效率巨異質接面高分子太陽能電池。混摻高電洞遷移率共軛高分子與二氧化鈦奈米桿具備形成有效率雙聯通的電子及電洞傳導相的潛力，以不同的元件製備條件進行嘗試以取得最佳化效率。對於巨異質接面影響電荷分離與電荷傳導的因素進行研究的結果指出，二氧化鈦奈米桿表面性質以及以旋轉塗佈製膜的溶劑都對於元件效率有很大的影響。
第三部分的研究中，凱文探針力顯微鏡被用以研討不同混摻比例聚(3-己烷噻吩)與二氧化鈦奈米桿高分子材料表面的奈米結構型態，高分子-奈米顆粒的聯通路徑，與光生電荷產生與分佈的狀態。我們並且探討聚(3,4-乙烯基二氧噻吩)：聚(苯乙烯磺酸鹽)層與二氧化鈦奈米桿層在混摻聚(3-己烷噻吩)與二氧化鈦奈米桿高分子太陽能電池中的角色。直接的光生電荷轉移可以被量測到發生在奈米維度的聚(3-己烷噻吩)豐富區域及二氧化鈦奈米桿豐富區域之間。利用增加的聚(3,4-乙烯基二氧噻吩)：聚(苯乙烯磺酸鹽)層或二氧化鈦奈米桿層，有效率的電子阻礙或收集作用亦被觀察到。聚(3-己烷噻吩)與二氧化鈦奈米桿混摻比例對於光生電荷的產生數目有決定性的影響。在混摻材料中具有高比例的二氧化鈦奈米桿可得到較細微的相分離與最多的光生電荷數。利用增加的聚(3,4-乙烯基二氧噻吩)：聚(苯乙烯磺酸鹽)層與二氧化鈦奈米桿層，可以幫助電子較易於分佈於表面，有利於被鋁上電極收集。

關鍵字

二氧化鈦 ； 奈米桿 ； 高分子 ； 太陽能電池 ； 光伏

並列摘要

The bulk heterojunction polymer solar cells composed of a mixtures of electron donor-acceptor interpenetrating network, such as using the polymer:fullerene, polymer:polymer and polymer:nanocrystal have been achieved highly efficient photovoltaic conversion. TiO2 nanocrystal is an environmentally friendly material which possess great potential to be introduced into the in the polymer solar cells as a second component owing to its excellent physically and chemically stability. Usually, TiO2 serves as the electron acceptor after the charge separation at the hetero-interface and then conducts the electron in the polymer solar cells. The usage of the polymer- TiO2 isotropic nanocrystals blend in the polymer solar cells that has been proposed in the prior studies provides the advantages of ease of fabrication as well as good organic-inorganic interface. Also, prior studies on charge transfer in hybrid MEH-PPV:TiO2 nanorods suggest this material can be a promising material for photovoltaic conversion. However, the blended polymer:TiO2 nanorods photovoltaic device has not been fabricated and evaluated before.
In this work, we explore the potential of the usage of the titanium dioxide nanorods in the polymer:nanocrystal photovoltaic cells. The 1-dimensional nanorods are preferable due to the offering of direct path for charge conduction and therefore are suitable to be acting as a component for constructing an efficient charge transport network in the bulk heterojunction polymer solar cells that we proposed and fabricated.
In the first part of this study, the bulk heterojunction devices made of MEH-PPV and titanium dioxide are fabricated. We propose to insert a thin layer of TiO2 nanorods between the photoactive material and the top Al electrode within the device. The TiO2 nanorods layer can serve as the electron-transporting-hole-blocking layer and leading to a 2.5 fold improvement in short circuit current density. The power conversion efficiency of 2.2 % under illumination at 565 nm and the maximum external quantum efficiency of 24 % at 430nm are achieved. A power conversion efficiency of ~0.5% is obtained under A.M. 1.5 illumination.
A high mobility polymer, poly(3-hexylthiophene) (P3HT), in combination with TiO2 nanorods are used to construct highly efficient bulk heterojunction solar cells in the second part of this work. The blending of high mobility polymer and TiO2 nanorods offers the potential for formation efficient bi-continuous conduction phases for respective electron and hole transport. Various device fabrication parameters have been tested to obtain optimal efficiency. The factors that change the charge separation or charge transport within the bulk hetero-junction, such as the TiO2 surface ligand and the solvent for spin coating the active layer has shown to greatly affect the device efficiency. A power conversion efficiency of 0.83% has been achieved.
In the third part, the Kelvin Probe Force Microscopy (KPFM) is applied to study the surface nano-structured morphology, the polymer-nanocrystal percolation paths as well as the light induced charge generation within the P3HT/TiO2 nanorod hybrid material in various D-A ratios which influence the interface area, conduction paths and film morphology. We also investigate the roles of PEDOT:PSS layer and TiO2 layer in a P3HT:TiO2 nanorods photovoltaic devices by KPFM. Directional photo-induced charge transfer in the nano-scale domains of P3HT rich and TiO2 nanorods rich regions and efficient electron blocking or collecting on the surface with additional layers are clearly seen. The blending ratios of P3HT with respective to TiO2 nanorods play an important role in determining the photo-induced charge generation. Finer scale of phase separation and highest numbers of charges are obtained within the film of high content TiO2 nanorods(72wt%). The inclusion of PEDOT:PSS and TiO2 nanorods layer in the device can facilitate the electron present on the surface to the Al electrode.

並列關鍵字

titanium dioxide ； nanorod ； polymer ； solar cell ； photovoltaic

參考文獻

Chapter 1

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