學者對於PTB7及PC71BM組成的有機太陽能電池已研究多時，尤其是針對製程中加入添加劑DIO的有無，但薄膜結構和載子傳遞路徑之間的關係還尚未釐清。我們團隊利用互補式的X光及中子反射法，輔以原子力顯微鏡、略角小角度／廣角度散射儀、以及電子能譜儀的探測，解析出隨縱深的成分組成分布圖，並聯結膜方向及縱深方向的膜結構與光電轉換效率之間的關係。根據空洞含量的多寡，在縱深方向可分成三個區域，包含表層、主層、及介面層。對於N-1.5薄膜來說，也就是薄膜不加DIO且成分重量比為1.5，我們發現高含量空洞（高於36 vol%）和長軸長270 奈米的扁橢形PC71BM聚集在表層、不厚的主層、以及充滿空洞（高達18 vol%）的介面層。介面層空洞的存在可能阻斷最有效率的電洞傳遞路徑。相反地，對於加入DIO的D-1.5薄膜來說，它由含有長軸長30奈米PC71BM橢球的平緩表層、材料分布均勻（PC71BM：53 vol%；PTB7：44 vol%）且較厚的主層、以及較窄的介面層組成。我們的結果顯示DIO的加入能夠改善薄膜沿著膜方向及縱深方向的結構，尤其是消除薄膜的分層結構。此外，DIO的加入也能促使薄膜在成分上達到理想的混合，讓PTB7和PC71BM有近乎相匹配的成分比例，因此我們能獲得高電轉換效率的薄膜。

PC71BM-based organic solar cells with thieno[3,4-b]thiophene‐alt‐benzodithiophene copolymer (PTB7) processed with or without diiodooctane (DIO) have long been investigated, but the relationship between nano-structure and charge transportation remains unclear. Here we utilize the contrast variation of X‐ray and neutron reflectivity, along with the measurement of atomic force microscopy (AFM), simultaneous grazing incident wide- and small-angle scattering (GIWAXS/GISAXS) and X-ray photoelectron spectroscopy (XPS), to reveal the composition profile and to relate the film structures both in in-plane and in-depth direction to device performance. Three regimes along film-depth direction distinguished by porosity contents are surface layer, main layer and interface zone, respectively. For N-1.5 film, the film composed of optimized PC71BM/PTB7 weight ratio of 1.5 with DIO, higher content of porosity fv ≧ 36 vol% and large PC71BM oblate-shaped domains of 2a = 270 nm gathering on the surface layer, narrow thickness of main layer, and the interface zone with porosity contents up to 18 vol% are revealed. The existence of porosity near interface possibly disconnects the short-cut routes for hole transportation. In contrast, for the DIO-added D-1.5 film, smooth surface layer with small oblates of size 2a = 30 nm, thicker main layer with evenly distributed composition (fv,PCBM = 53 vol% and fv,PTB7 = 44 vol%), and narrow interface layer are revealed. The results obtained show that DIO improves both the in-plane and through-thickness morphology, especially removing the stratified features of films without DIO. Moreover, the addition of DIO induces an ideal mixing in blend ratio, reaching the matched concentrations of PTB7 and PC71BM, hence the optimized device performance.

ABSTRACT III
LIST OF FIGURES V
LIST OF TABLES IX
1. Introduction 1
1.1 Background 1
1.2 Objectives and approach 2
2. Experimental details 3
2.1 Sample fabrication: 3
2.2 Instruments 3
3. Data analysis 6
3.1 Complementary scattering of XR/NR 6
3.2 Contrast variation with XR/NR for vertical composition distribution de-convolution 8
3.3 GISAXS analysis 9
4. Results 11
4.1 Structural features of neat polymer and fullerene films 11
4.2 Contrast variation of X-ray and neutron reflectometry 14
4.3 DIO effects on vertical phase separation 17
4.4 Local phase separation and polymer crystallization 21
4.5 Construction of a 3-D model regarding DIO effect 32
5. Discussion 34
5.1 Morphological effect on PCE 34
5.2 Relationship between PTB7/PC71BM composition and PCE. 34
5.3 Vertical and local phase separation mechanisms. 34
6. Conclusion 37
Reference 38
Appendix A. Similar Observation in blend ratio of 1 40
Appendix B. Similar Observation in blend ratio of 2 46

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