國立台灣大學林清富教授實驗室

研究領域摘要

主題一:有機無機太陽能電池

研究人員:黃敬舜、周貞佑、劉孟岳、蔡國華、王鼎鑫、陳柏諭、林信伯、林宇宏、王膺傑

英文摘要:

Polymer solar cells (PSCs) have attracted much attention due to their great potentials for large-area, light-weight, flexible, and low-cost devices. Recently, bulk-

heterojunction (BHJ) solar cells based on poly(3-hexylthiophene) (P3HT) and (6,6)-phenyl C61 butyric acid methyl ester (PCBM) with power conversion

efficiency (PCE) of 4-5 % have been reported. However, control of the transportation of the charge carriers at interfaces is one of the most challenging issues in

the improvement of PSCs. It has been reported that the insertion of an interlayer between the organic layer and the anode improves the device performance. To

date, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and transition metal oxides have been employed for this purpose. However, only

the deposition of PEDOT:PSS layer can be easily processed by solution-based coating techniques. Most transition metal oxides as the anode interlayers are

deposited by the vacuum evaporation, which could detract from the advantage of the ease of PSC fabrication. Using solution-processed transition metal oxide as

the anode interlayer for improving the PSC performance has seldom been reported.

The aim of this work is to realize a low-cost and high-efficiency inverted PSC hybridized with ZnO nanorod arrays by introduction of a solution-processed

vanadium oxide (V2O5) as the anode interlayer. Our investigation shows that the photovoltaic device performance is improved by the introduction of the V2O5

interlayer due to the efficient suppression of the leakage currents at the organic/metal interface. Compared to the conventional BHJ structure (indium tin oxide

(ITO)/PEDOT:PSS/active layer/Al), the use of the inverted structure overcomes some obstacles such as the facile oxidation of Al and the electrical

inhomogeneities of PEDOT:PSS as well as its corrosion to ITO. The inverted PSCs utilize an air-stable high work-function electrode as the back contact to

collect holes and metal-oxide nanostructures at the ITO to collect electrons. Furthermore, it has been reported that the ZnO nanorods have beneficial effects of

collecting and transporting electrons in the inverted PSCs hybridized with the ZnO nanorods. Our works combine these advantages of V2O5 interlayer and ZnO

nanorods, which thereby suppress the leakage currents and improve the collection and transportation of the charge carriers, resulting in enhancements of PCE,

open-circuit voltage (VOC), and fill factor (FF) of the devices. In addition, the V2O5 interlayer can serve as an optical spacer to increase light absorption,

leading to an increased short-circuit density (JSC). Moreover, the V2O5 interlayer and ZnO nanorod arrays both are fabricated from simple solution-based

processes, which are well-suited for use in high-throughput roll-to-roll manufacturing.

Although PEDOT:PSS layer can be solution processed, its hygroscopic nature is likely to form insulating patches due to the water adsorption, thus degrading the

devices. In contrast, V2O5 is relatively insensitive to water and stable in air. The solution-processed V2O5 interlayer can serve as a barrier preventing oxygen or

water from entering and degrading the photoactive layer. In addition, this approach does not need annealing treatment like PEDOT:PSS nor vacuum equipments,

so it is simple, expeditious, and effective. This is very important for commercial realization of low-cost and large-area printed solar cells.

Fig 1. (a) Device structure of the photovoltaic cells. (b) Energy band diagram for the photovoltaic cells in this study.

Fig. 2. The J-V curves of the photovoltaic devices with the V2O5 interlayer from various concentrations under 100 mW/cm2 AM 1.5G irradiation.

Fig. 3. (a) AFM images of the photoactive layers covered with and without the optimum V2O5 interlayer. AFM image scans are 5×5 μm.

(b) Transmissionspectrum of the V2O5 layer (from the 100 μg/ml V2O5 colloidal solution) on a glass substrate. (c) XRD spectrum of V2O5.

Fig. 4. (a) IPCE spectra for the devices with and without the optimum V2O5 interlayer.

(b) The change in absorption spectrum [Δα(λ)] and the difference in IPCE spectrum [ΔIPCE(λ)] resulting from the insertion of the optimum V2O5

interlayer. The inset is a schematic of the optical beam path in the both samples. The variables are defined in the text.

中文摘要:

與現在矽材料太陽能電池相比，新型有機太陽能電池不僅生?成本低廉、重量輕，而且像塑膠薄膜一樣薄、透明、能夠彎曲，適合製作各種形

狀的太陽能電池，可以廣泛應用在通訊、建築、交通、照明、時尚等領域。新一代有機太陽能電池不僅是對全球氣候變化時期環境保護的貢獻

，而且具有很大的經濟潛力。在元件結構上，一般是使用塊材異質接面(Bulk-heterojunction)結構，以poly(3-hexylthiophene) (P3HT)為電洞傳輸材

料，(6,6)-phenyl C61 butyric acid methyl ester (PCBM)為電子傳輸材料，利用其具大面積激子分離區域的優點，使元件有較佳的效率。然而，載子

在有機/電極介面處的傳輸特性仍有許多改善的空間。文獻指出在有機層與電極中間插入一中介層(interlayer)對於元件效率的改善將有助益。以電

池陽極為例，可以插入poly(3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS)或過渡金屬氧化物作為此用途。然而，只有PEDOT:PSS層

的製作可用簡單的溶液塗佈方式來達成，而作為陽極中介層的過渡金屬氧化物層大多需要真空蒸鍍設備來製作，如熱蒸鍍、濺鍍、電子槍蒸鍍

等。這些真空設備與溶液塗佈方式相較顯得相對昂貴且耗時，亦不利於大面積的應用。有鑒於此，我們的目標是開發出溶液態製備過渡金屬氧

化物作為陽極中介層，並應用於發展低成本且高效率之有機太陽能電池。

我們研究發現導入一層以溶液態製備的五氧化二釩(V2O5)可抑制元件的漏電流進而提升太陽能電池的效率。我們的元件結構與常見的有機太陽

能電池稍不相同。常見的有機太陽能電池結構是氧化銦錫(indium tin oxide, ITO)/PEDOT:PSS/有機主動層/鋁，我們使用的是倒置式結構，此結構以

穩定且功函數高的金屬作為背面電極來收集電洞，同時以ITO為陰極來收集電子，這改善了傳統上鋁電極的易氧化問題與PEDOT:PSS的電荷不均

勻性問題，使電池壽命得以提升。我們結合了V2O5中介層與ZnO奈米柱陣列的優點，除可抑制元件內部漏電流外，也兼顧了電荷的收集與傳輸

，使得有機太陽能電池的效率獲得提升。此外，我們發現V2O5中介層也具有optical spacer的功能，可增加光的吸收，進而增加電池的電流密度。

而且，V2O5中介層與ZnO奈米柱陣列均是以簡單的溶液法製備，非常適合捲軸式的製程(roll-to-roll manufacturing)。

雖然PEDOT:PSS層可以溶液態製備，但它具有吸水性，當吸收了空氣中的水氣後會在PEDOT:PSS層內產生insulating patches，使得元件效率下降。

相反地，V2O5中介層對水氣不敏感，在空氣中相當安定，因此，以溶液態製備的V2O5中介層可作為一屏障，防止水氣與氧氣進入有機層內，使

元件在空氣中較為穩定。此外，由於不需要回火或烘烤，更不需要昂貴的真空蒸鍍設備，我們所使用的方法是相當便利且有效，有助於實現低

成本大面積的有機太陽能電池，對於有機太陽能電池的商業化相當重要。

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