以克爾文探針顯微鏡研究奈米尺度下聚三己基噻吩與二氧化鈦奈米桿混摻材料之表面形貌與表面電位

Abstract

掃描力探針顯微鏡以其奈米碳針可以對材料表面的微結構進行觀察，迄今在奈米尺度的研究上貢獻良多。其中，克爾文探針顯微鏡利用導電探針與試片的靜電反應可以直接觀察試片表面電荷的行為，可以量測光電元件的運作情形；又由於克爾文探針顯微鏡是在非接觸與非破壞的方式下運作，該顯微鏡適用於軟性材料與有機材料。本篇研究主要是以克爾文探針顯微鏡探討聚三己基噻吩與二氧化鈦奈米桿混摻材料層在沒照光與照光的情況下電荷的運作情形，並藉此觀點探討元件的最佳製程參數；而我們將高分子量的聚三己基噻吩(66k Da)溶於氯苯後與以寡聚體三己基噻吩為表面改質過後的二氧化鈦奈米桿進行混摻並旋鍍成混摻薄膜，由克爾文探針顯微鏡觀察到該薄膜在照光後其表面的電子密度有顯著的提升，該製程參數製成的太陽能電池也有最高的效率表現。至此，本研究發現表面電荷與太陽能電池的效率表現有明顯的關聯性，而藉由克爾文探針顯微鏡量測混摻薄膜而得的表面電荷可以定性地表現出太陽能電池的效率表現。此量測方式提供了一種快速了解有機太陽能電池製程品質的分析方法，可以大幅的縮減一般有機太陽能電池分析與製程的週期。

As a nanoscale microscope, the scanning force microscope is crucial to make an insight into the performance of material in the operation of optoelectronic devices. Kelvin probe force microscope, one of SFMs, can directly monitor the behavior of the surface charge by the electrostatic force between the conductive tip and the sample. Its non-contact and non-destructive characteristics allow applications on soft and organic materials. In this study, we monitor series of surface charge by KFM on poly(3-hexylthiophene)(P3HT) and TiO2 nanorod hybrid active layers for solar cells in dark or under illumination, which enabled us find an optimal processing condition for the device. Under the illumination, the hybrid film made from high molecular weight P3HT (66 kDa) and oligomer 3HT-COOH modified TiO2 nanorods shows the largest electron accumulation on the surface and exhibit the best solar cell efficiency. The KFM measurements also provide the knowledge in the relationships between surface potential and device performance for P3HT:TiO2 hybrid solar cell. These results can understand the device performance qualitatively by single KFM measurement on the active layer, without fabricating a complete device. It is a valuable technique to shorten the development and hybrid solar cells.