先前以poly(3-hexylthiophene) (P3HT)與[6,6]-phenyl-C61-butyric acid methyl ester (PCBM)溶於氯苯(Chlorobenzene, CB)進行旋轉塗佈實驗的研究中，旋轉塗佈初期於薄膜表層形成的溶質富含層會在底層的溶劑藉由離心力甩乾與揮發後形成最終的薄膜，本研究探討在加入不同濃度的高沸點添加劑(1,8-octandithiol，OT)，利用臨場垂直光學干涉、掠角入射小角X光散射與掠角入射寬角X光散射，研究OT對P3HT/PCBM溶液旋轉塗佈成膜過程中的影響。摻入的高沸點添加劑易累積於表層，導致CB的揮發效率變差，使得PCBM與P3HT的聚集與結晶發生的時間延後；因為PCBM對OT的溶解度相對於P3HT較好，使PCBM的延遲情形更為嚴重。隨著下層溶質濃度的增加，累積於表層的OT會擴散回下層進而影響整體薄膜結構。最終在添加OT的樣品中，P3HT結晶度會增加而PCBM聚集程度則反之降低。

In a recent study, formation of the solute-rich skin layer and the solvent-rich bottom layer in spin-coating process of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) thin film was demonstrated. After the bottom layer diminished, the solute-rich skin layer then condensed into the final film, indicating the final film morphology is determined by the air-liquid interface. In this study, we focus on the P3HT/PCBM system with different amount of high boiling additive 1,8-octandithiol (OT) to investigate the film formation during spin coating by in-situ Grazing-Incidence Small-/Wide-Angle X-ray Scattering (GISAXS/GIWAXS) and normal optical interferometry. Due to the relatively higher evaporation of CB, high boiling temperature OT will accumulate on the surface and delay the crystallization of P3HT and the aggregation of PCBM. Compared to P3HT, PCBM has better solubility for OT, therefore the delay of PCBM aggregation is more serious than P3HT crystallization. Due to the increase of solute-rich layer concentration, surface-accumulated OT will diffuse back to the bulk film, causing the increase of P3HT crystallinity but decrease of PCBM aggregation.

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