二氧化鈦奈米晶體之表面改質應用於有機無機混摻太陽能電池之研究

Abstract

本研究探討導電高分子P3HT與二氧化鈦奈米桿的混摻系統中，二氧化鈦奈米桿的表面改質研究。預期藉由奈米桿的表面改質，提昇有機無機混摻太陽能電池的能量轉換效率。在此，表面改質乃是利用化學置換反應，去除原本存附於二氧化鈦奈米桿表面的非導電分子，並分別吸附二種導電性的界面改質分子（interface modifier），即酞菁銅（CuPc）的衍生物Cudye及末端具羧酸基的己基噻吩寡體（oligomer 3HT-COOH），以增進載子在予體、受體界面的傳輸性質。由定性及定量分析結果，可確認表面改質分子可於二氧化鈦奈米桿表面產生有效吸附。雖然由於其較少的吸附量，改質分子的存在不足以額外提昇混摻系統對光子的吸收，但系統中的激子分離效率卻可在改質後獲得很大程度的提昇；電子與電洞的再結合亦可被有效抑制。另外，在表面改質後，P3HT與二氧化鈦間顯示了更為相近的親疏水性，混摻薄膜中的高分子也具備較佳的結晶排列，因此可推測表面改質亦有助於提昇混摻系統中，有機相（P3HT）與無機相（二氧化鈦奈米桿）之間的相容性。藉由釐清表面改質分子在有機太陽能電池作用層中的角色與功能，本研究提供了一提昇太陽能電池效率的可行途徑。

This work presents the study of surface modification of TiO2 nanorod in bulk heterojunction composites based on poly(3-hexylthiophene) (P3HT) and TiO2 nanorods, trying to improve the performance of organic/inorganic hybrid solar cells. Surface modification of TiO2 was performed by replacing the insulating surface ligand (oleic acid) with two kinds of conductive, novel interface modifiers: the derivative of copper phthalocyanine (Cudye) and the regioregular 3-hexylthiophene oligomer with carboxylic end functional groups (oligomer 3HT–COOH). As surface modification was carried out, the hybrid system exhibited an improved charge separation by showing a more pronounced PL quenching. Also, back recombination between electrons and holes can be suppressed from the transient photo-voltage measurement, revealing a longer charge carrier lifetime. Furthermore, the compatibility between P3HT and TiO2 can also be improved after surface modification, as P3HT and modified TiO2 exhibited a more similar surface hydrophobicity (by contact angle measurement) and higher polymer crystallinity in the hybrid films (by XRD). All the data show that the oligomer 3HT-COOH is the better performed interface modifier than Cudye. By clarifying the functions and roles of interface modifier in the active layer of photovoltaic devices, this study provides a possible route for increasing the efficiency of organic solar cells.