運用共溶劑方法提升有機太陽能電池效率

Abstract

有機薄膜表面型態(morphology)之控制是提升共軛高分子太陽能電池效率的重要關鍵，針對這個方向，我們提出一個新穎的方法促使太陽能電池主動層材料P3HT/PCBM達成自主性排列(self-organized)的奈米結構。本研究是利用共溶劑方法，首先將主動層材料，P3HT及PCBM溶解在一較低沸點(高蒸氣壓)1.2-dichlorobenzene的有機溶劑中，另加入一個高沸點低蒸氣壓的溶劑(如1-chloronaphthalene或1,2,4-trichlorobenzene)攪拌均勻，塗佈後待其自然乾燥，即可進行下一道製程，無須等待長時間的揮發過程(或稱之為溶劑退火)，當1-chloronaphthalene或1,2,4-trichlorobenzene加入材料比例增加，可看出高分子太陽能電池光電轉換效率的變化。開路電壓(Voc)，並不會隨溶劑比例而降低，相反的，短路電流 (Jsc)與填充因子(FF)，卻有提升的趨勢，表示添加新溶劑材料確實有對元件效率有正面提升的效果，所以，光電轉換效率(Power Conversion Efficiency)，隨著添加比例而使元件效率有所提升。此外，從UV-Visible absorption spectra、X-ray繞射圖形(X-ray diffraction)與遷移率(mobility)得知，高分子的排列程度隨添加此高沸點溶劑的比例提升，因此相較於未添加高沸點溶劑的主動層，材料結晶性的增加促成短路電流(Jsc)的改善。此外，與溶劑退火相較起來，利用共溶劑較傳統溶劑退火製程步驟較為簡單且省時，且此方法有更高的太陽能電池效率。

The influence of solvent mixing on the device performance of polymer solar cells had been investigated. In this work, we used solvent mixtures, consisting of one solvent with a high boiling point, 1-chloronaphthalene (Cl-naph, bp = 259 oC) or 1,2,4-trichlorobenzene(TCB,bp=214 oC) , as the additive in o-dichlorobenzene (DCB, bp = 179 oC) to dissolve the P3HT/PCBM blends. Because of the lower vapor pressure of the solvent mixtures, the polymer films dried slower. With higher Cl-naph or TCB concentration in the solvent mixtures, the polymer chains have longer time to self-organize themselves. Further, from ultraviolet-visible absorption and the grazing incident XRD spectra, higher crystallinity of the polymer was also observed for the thin film prepared from the solvent mixture. Besides, the use of the solvent mixtures indeed improves the hole mobility.As a result, the higher degree of crystalline led to lower device series resistance, thereby increasing the performance of the photovoltaic devices. The device efficiency was improved by using the solvent mixture. Because no solvent saturated environment involved, the fabrication procedure has been simplified.