有機高分子光伏載體-受體系統的形態特性研究

Abstract

由高分子與富勒稀衍生物所製作的太陽能電池系統，已經被視為最有潛力的再生替代能源選項。在許多高分子與富勒稀的材料組合中，聚噻吩（P3HT）和苯基碳61丁酸甲酯(PCBM)是目前最被廣泛研究的題材。然而，最近的研究報導指出一個新的受體材料：茚-碳60雙加成物（ICBA），用來取代PCBM作為P3HT系統的新受體材料，其較高的最低未填滿軌域能階（LUMO），使得太陽能電池的效能獲得明顯的提昇。然而，除了能階的影響以外，深入的形態討論對瞭解ICBA和PCBM的元件效率的差異也會有幫助。 在這篇論文中，我們比較這兩個載體-受體混合系統：P3HT/PCBM和P3HT/ICBA的光譜以及形態特性，利用光學顯微鏡以及低掠角X光散射技術，我們發現不管是單一材料薄膜，或是混合載體-受體的薄膜，PCBM相對ICBA容易形成較大且規則的聚集或是結晶結構，和PCBM相較下，ICBA也相當程度的破壞P3HT的規則性排列。由於P3HT/PCBM系統可以形成較多、較大的規則相分離區域，P3HT/PCBM薄膜在高濃度PCBM摻雜的情況下，可以觀察到明顯的光學散射特性，然而這樣的特性在P3HT/ICBA的混合系統上並不明顯！這樣的結果表示，P3HT/ICBA的元件效率提昇並非來自主動層的形態品質提昇，而是其他的原因在元件效率提昇上產生更重要的影響

Solar cell technology based on polymer/fullerene composites are continuously gaining interest as a potential source of renewable energy. Among the composites, poly(3-hyxelthiophene) (P3HT) and [6,6]-phenyel-C61 butyric acid methyl ester (PCBM) are the most widely studied D-A combination. Recently, a new C60-based acceptor material indene-C60 bisadduct (ICBA) replacing PCBM as an acceptor in the P3HT/fullerene system is repoted to substantially improve the conversion efficiency of the solar cells owing to the higher LUMO level. However, the detailed morphological properties of the donor-acceptor composites would also be essential in understanding the difference in performance between the P3HT/PCBM system and the relatively new P3HT/ICBA system We report a comparative study on spectral and morphological properties of two blend systems for polymer solar cells: the donor material P3HT in combination with the acceptor material of either PCBM or ICBA that was reported to enhance efficiencies of polymer solar cells. Optical microscopy and grazing incidence X-ray scattering reveal the stronger tendency of PCBM to from larger and more ordered domains/grains than ICBA either in pure or blend films. Compared to PCBM, the presence of ICBA also substantially perturbs the organization and longer-range ordering of P3HT in increasing the ICBA ratio in blends. With larger and more ordered phase-separated domains, the P3HT/PCBM blend films exhibit significant optical scattering at higher PCBM ratios. Yet, such optical scattering is not significant for P3HT/ICBA blends (even with high ICBA ratios). Overall, results here suggest the reported higher efficiencies of P3HT/ICBA solar cells (vs. P3HT/PCBM cells) cannot be attributed to larger and/or more ordered phase-separated donor-acceptor domains and other characteristics play more important roles in this case.