本研究希望藉由高分子與奈米碳球之間的作用力，減緩奈米碳球聚集的趨勢。進一步以混摻薄膜中奈米碳球與高分子的相分離，作為調控奈米碳球晶相成長的機制。這可以使得奈米碳球的相分離與晶相成長，成為提升太陽能電池效能的契機。
由探討聚芴高分子(PFs)與奈米碳球混摻系統的結果發現，於PFO/PCBM混摻系統中，PFO與PCBM傾向發生成分間的相分離，僅有微量的PFO能與PCBM互溶混合。我們也利用混摻側鏈長度較長的的聚芴高分子PF12，探討側鏈長度帶來的影響。實驗結果發現，和PFO相比，PF12與PCBM的互溶性較佳。於混摻比例同樣為5/95重量百分率時，PFO與PCBM已經形成可觀的相分離，而PF12與PCBM還是呈現相當均勻的形貌。表示側鏈長度的增加，可以使得聚芴分子較易與PCBM混合。
接著探討PCBM於相分離系統中的晶相成長，由實驗結果發現，PCBM於PFO/PCBM混摻比例為5/95重量百分率的薄膜中晶相成長，主要是發展成球晶的結晶型態。由初始狀態的相分離形貌，到於低溫持溫所形成的PCBM小球晶，最後到於高溫持溫發展的大尺寸PCBM球晶。而提高PFO的混摻比例至10/90重量百分率時，發現PCBM於高溫持溫能發展出PCBM的單晶連續網路。
相較於PFO，PF12/PCBM均勻薄膜於相對低溫持溫時，PCBM就能發展出大範圍的晶相成長。表示PCBM於PF12/PCBM混摻薄膜中，較易擴散，結晶成長不會受到分子供給效率的影響，促使PCBM發展球晶的結晶型態。即使提高PF12的混摻比例，也無法發展出如PFO/PCBM混摻薄膜中的PCBM網狀的單晶通路，但可以觀察到樹狀晶的出現。

SUMMARY
In this study, the phase separation behavior of a binary blend system of poly(9,9-di-n-octyl-2,7-fluorene)(PFO)/[6,6]-C61-butyric acid-methyl ester(PCBM) has been studied. The constituent component PCBM is a derivative of carbon allotrope, and is widely used in solar cell. First, the phase separation of PFO and PCBM has been observed by transmission electron microscopy (TEM), and the increase of mixing ratio of polymer was found to significantly widen the networks of phase separation.
In addition, the effect of annealing temperature on PCBM crystallization behavior in PFO/PCBM blend has been explored. When we increased the mixing ratio of PFO or annealing temperature, diffusion and supply efficiency of PCBM would decrease as being hindered by mixed polyfluorenes. When the diffusion efficiency of PCBM is significantly lessened, dendritic crystal of PCBM were widely developed instead of spherulites. With the increase of side-chain length of blended polyfluorene, more free volume is created in mixture, which improves diffusion efficiency of PCBM and thus efficiency of PCBM crystallization in blends.
In summary, the blending of conjugated polymers was found as a promising approach to tailor the distribution of PCBM within thin film. Corresponding influence on diffusion efficiency of PCBM has not been unveiled before and appears capable of tuning crystallization behavior of PCBM and helpful for the potential application.

INTRODUCTION
PCBM is widely used as a constituent component in the active layer of organic solar cells and serves to establish the network capable of receiving and transporting excited electrons in the active layer. The spread and distribution patterns of PCBM crystalline phase would influence the efficiency of collecting excited electrons provided by neighboring domains of conjugated polymers and is thus critically important for the performance of solar cell. If PCBM can be developed as a continuous crystalline phase without defects, it will provide efficient transportation of excited electrons to the electrode. However, the strong aggregation tendency of PCBM make it difficult to manipulate the growth and spread of PCBM crystals. This study attempts to adopt the interactions between conjugated polymers and PCBM to prevent severe aggregation of PCBM, and results in networks of phase separation as a mechanism to control the spread and growth of PCBM crystals. It can be developed as a feasible mechanism to enhance the efficiency of solar cells.

MATERIALS AND METHODS
PFO and PCBM were dissolved in chloroform with different ratios and the solution was heated at 55 oC for overnight.
PFO/PCBM solutions were spin-coated on the glass substrate at 500 rpm for 20 s and then 2000 rpm for 30 s. The spin-coated films were annealed at different temperatures about one hour in vacuum hot stage, and then rapid quenched to room temperature. Finally, the X-ray diffraction, transmission electron microscopy(TEM) and atomic force microscope(AFM) were used to observe the PCBM crystallization behavior.

RESULTS AND DISCUSSION
1.
The film morphologies and the phase separation of PFO and PCBM have been observed by TEM. Only a few amount of PFO can be mixed with PCBM. Phase separation of PFO and PCBM might occur in the solution. Moreover, this phase separation occurred due to the saturation of the solute concentration.
We found PF12 has better miscibility with PCBM. PFO formed obvious phase separation with PCBM, but PF12 and PCBM blend showed fairly uniform morphology at the ratio 5/95. It indicates that an increase in the length of side chain can help polyfluorene and PCBM mix together.

2.
The effect of annealing temperature and mixing ratio on PCBM crystallization behavior in blend system of PFO and PCBM has also been explored. When the ratio of PFO / PCBM was 5/95, the crystallization of PCBM in blend film developed spherulite crystals mainly. If we increased the ratio of mixed PFO to 10/90 and annealed at high temperature, it has been found that PCBM would develop network of single crystals.
3.
Next, we discussed the effect of side-chain on crystallization behavior of PCBM in blend system of PF12 and PCBM. PCBM is able to develop spherulite crystals of a large scale as being mixed with PF12 when annealing temperature was relatively low. Upon mixing with PF12, the diffusion of PCBM appears easier and crystallization growth is less retarded by the supply of PCBM molecules. Therefore, the crystallization of PCBM in blend system of PF12 and PCBM developed spherulite crystals mainly. If we increased the ratio of PF12, PCBM could not develop network of single crystals as the crystallization of PCBM in blend system of PFO and PCBM. But we can observe dendritic crystals appeared.

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