以表面改質工程增進聚三己基噻吩/二氧化鈦奈米桿混摻太陽能電池的效率

Abstract

有機無機混摻材料是一種新興的光電材料可應用於廉價及可撓曲的太陽能電池的製作。本研究以二氧化鈦(TiO2)奈米桿取代在塊材異質接面P3HT/PCBM太陽能電池系統中的PCBM當作電子受體的材料。因為對環境低污染和廉價的TiO2奈米桿製作的太陽能電池比P3HT/PCBM系統能夠提供更好的熱穩定性。在塊材異質接面的結構中，適當的相分離不僅可以提供偌大的電子受體與予體間的界面進行有效的電荷分離，並且產生連續的電荷傳導路徑。 在我們TiO2奈米桿的系統中，TiO2奈米桿是在油酸的環境中經由溶膠凝膠法(sol-gel)所合成，隨後絕緣性的油酸部分被吡啶取代。雖然芳香烴類的吡啶會略為增加電子的傳輸，但是卻降低P3HT和TiO2奈米桿的相容性。因此我們藉由表面工程技術，使用不同的有機分子改質TiO2奈米桿表面，以增進P3HT/TiO2奈米桿混摻太陽能電池效率。在TiO2奈米桿上的吡啶先被較疏水性的吡啶衍生物如2,6-lutidine或4-tertbutyl-pyridine所取代。元件的開路電壓從0.71V分別增加至0.76V和0.78V，因為2,6-lutidine和4-tertbutyl-pyridine的偶極特性以及較親和的界面，減少電荷的再複合。我們進而設計兩個導電性無金屬的有機染料W4和WF，共軛和推拉電子系統的主鏈結構，使兩種染料分子的能階介於P3HT和TiO2奈米桿之間，並形成有利於電荷傳輸的階梯式能階。染料會在TiO2奈米桿被吡啶衍生物改質之後再接支於表面上，同時藉由一些元件量測分析，例如不同光強度照射、藉由線性增加電壓抽取電荷、空間電荷限制電流等方法，我們發現在P3HT/TiO2-dye的太陽能電池系統中，電荷載子傳輸的大幅提升以及電荷再複合損失機制的減低 TiO2奈米桿經由4-tertbutyl-pyridine以及W4染料改質之後，在表面包含了最少的絕緣油酸以及最多的W4染料分子，與只經吡啶改質的TiO2奈米例子相較，電池的性能大大的改善，其開路電壓由0.71V增至0.85V、短路電流由1.17 mA/cm2增至2.48 mA/cm2、填充因子由48.23% 增至64.40%，光電轉換效率由0.40%增至1.36%。

Organic–inorganic hybrids have emerged as a novel class of optoelectronic materials for low cost and flexible photovoltaic applications. We have replaced PCBM acceptor by TiO2nanorods in the bulk heterojunction P3HT/PCBM solar cell system. The environmental friendly and low cost TiO2 can provide more thermal stable solar cell than that of P3HT/PCBM. In the bulk heterojunction structure, adequate phase separation provides not only large interfaces between donor and acceptor for efficient charge separation but also generates continuous conducting path for effective charge transport. In our TiO2 nanorod system, the TiO2 nanorod were synthesized through sol-gel process in oleic acid, and then a part of insulating oleic acid was replaced by pyridine. Although the aromatic pyridine has improved the electron transport slightly as compared with insulating oleic acid, the compatibility between P3HT and TiO2nanorod was reduced. Therefore, we have done interface engineering using different organic molecules on the surface of TiO2 nanorod to improve the solar cell efficiency of P3HT/TiO2 nanorod hybrid. Pyridine was replaced by more hydrophobic pyridine derivatives such as 2,6-lutidine and 4-tertbutyl-pyridine. The Voc of the device was increased from 0.71V to 0.76 V and 0.78 V, respectively as compared with pyridine due to the reduced charge recombination at improved interfaces by using more compatible pyridine derivatives interface modifiers. We have designed two conducting metal-free dye, W4 and WF with conjugating and donor-acceptor structure. They exhibit bandgap between P3HT and TiO2 nanorod which can form a cascade energy level to facilitate charge transport. They were placed on the TiO2 after the pyridine derivatives treatment. Several device measurement analyses like power dependent method, electrochemistry impedance spectroscopy (EIS), charge extraction by linearly increasing voltage (CELIV) and space charge limited current (SCLC) method were used to study the device physics of P3HT/TiO2 nanorod solar cell fabricated from dye modified TiO2 nanorod. The device efficiency is greatly improved using 4-tertbutylpyridine and W4 treated TiO2 nanorod on its surface because the TiO2 containing the least amount of insulating oleic acid and the most amount W4 dye. The device exhibits the performance of power conversion efficiency 1.36%, Voc=0.85 V, Jsc=2.48 mA/cm2, FF=64.40% as compares with device made from pyridine-treated TiO2 nanorod having PCE=0.40%, Voc=0.71 V, Jsc=1.17 mA/cm2, FF=48.23%.