混合溶劑用於大面積可撓式有機太陽能電池製程之研究

Abstract

近年來，隨著有機材料在太陽能電池相關研究上的蓬勃發展，如何把實驗階段的有機導電太陽能電池透過放大製程製作出大面積未來可量產化的商品已成為一個重要的課題。在本研究中，我們利用有機導電高分子材料具有濕式製程的優點來大面積塗佈有機太陽能元件於可撓式基板上，製作出比矽晶圓來的更輕巧方便又可折疊的太陽能電池。

我們使用濕式製程將溶液狀態的光電高分子(P3HT:PCBM)塗佈於塑膠基板(PC/IZO)上製備有機主動層，並利用混合溶劑系統(cosolvent)在軟板上得到有效的相分離與表面結構。在表面結構上，使用吸收光譜(UV-VIS)、X光繞射儀(XRD)、穿透式電子顯微鏡(TEM)來分析元件的表面形態和內部結構。在地表太陽光模擬光源(AM1.5)照射下，以電性分析儀來量測太陽能電池的效率。最後，透過分析混合溶劑中的溶解度參數(solubility parameter)，我們發現了混合溶劑系統的關鍵因子為溶解度差異，並透過平衡混合溶劑對於個別光電高分子的溶解度參數，可以有效的改變主動層的表面形態(morphology)與控制P3HT的結晶程度(crystallinity)，最終單一有機太陽能電池元件在軟板上不透過後製加熱(post-annealing)的效率可以達到3.2%。

透過觀察有機導電太陽能電池放大化的過程，我們發現原件尺寸的大小，模組的串並聯、製程上的控制，都再在影響太陽能電池的電阻值、FF值與效能轉換能力。如何有效的透過溶劑改質得到最佳的薄膜品質成為了大面積有機太陽能電池模組製造的關鍵。最後，最佳化的模組為在有效面積為24 cm2下，可輸出電流(Isc)達到31 mA、電壓(Voc)達到1.8 V、最大功率(Pmax)達到16.9 mW，達到目前國際的最高水準。未來的前景可以預期。

During the last few years, increased effort and work has been devoted to the development of solar cells based on conjugate polymer, however, there is a lacking of knowledge on how to take the laboratory stage organic photovoltaics into next level commercialized products. In this thesis, we report the large area, interconnected polymer solar cell modules on flexible substrate to outperform the traditional silicon solar cells in turn of light-weight, flexibility, and convenience.

Here we use cosolvent system to assemble photoactive polymer blend, regioregular poly(3-hexylithiophene) (P3HT) : [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) on the flexible polycarbonate (PC) substrate coated with indium zinc oxide (IZO) and to induce effective phase separation in the active layer without the need of high temperature annealing process which is proven to be harmful to the plastic substrate. The morphological characterization is carried out with ultraviolet-visible spectroscopy (UV-VIS) and x-ray diffraction (XRD) and transmission electron microscopy (TEM). The IV characteristics of solar cell devices are performed under solar simulator (AM1.5). Through analyzing and balancing the solubility parameters of various cosolvent combinations towards each polymer blend material, we are able to control the morphology and crystallinity of P3HT material inside the polymer blend thus achieve a highest efficiency of 3.2 % for single solar cell device on plastic substrate without post annealing.

In the second part of this thesis, we analyze the factors that determine solar module’s internal resistance, fill factor and power conversion efficiency. According to the experimental results, we have found that area of single cell, number of connected module, and solvent system used in manufacturing are all critical factors in optimizing overall performance of organic solar cell module. Hence, two different connection schemes (series and parallel) are applied to maximize the performance of solar modules. With a total of 24 solar cell devices (total active area = 24 cm2) interconnected on the 7 cm × 7 cm flexible panel, our organic solar module can output a short circuit current of 31 mA, an open circuit voltage of 1.8 V and a maximum power of 16.9 mW.