旋轉塗佈在有機太陽能電池的製備過程中扮演重要的角色，然而在先前的研究中，大多集中在純溶劑或是混合溶液系統(P3HT/PCNM)的討論，因此在本篇文章中我們將重點放在單一系統溶液(P3HT)的探討上。我們利用垂直入射光學反射儀輔以臨場低掠角小角度/廣角X光散射儀觀察P3HT高分子膜在旋轉塗佈的過程。根據垂直入射光學反射儀的結果，若直接假設整個系統為單一液體層，可以將整個旋轉塗佈的過程分為三個階段：1.流體主導階段2.揮發主導階段3.急凍階段。而當我們進一步分析，假設整個系統是由多層組成的，我們發現會有約30 奈米厚且高折射率的薄層覆蓋在氣液介面處，並且此一薄層出現的時機大致與我們在廣角X光散射儀偵測到P3HT結晶的時間吻合。從廣角散射的結果顯示，從揮發主導階段到急凍階段的過程中，高分子的相對結晶度及晶粒大小快速達到飽和值，過程中只有些微的變化;同時的我們從小角度散射的結果可得知在氣液介面處的薄層是由長軸長200奈米、短軸長10奈米的扁橢球組成，而這些扁橢球裡面充滿了P3HT結晶;若進一步觀察這些橢球的大小及數量可以發現，橢球之大小並無顯著改變，僅有數量有些微的增加。綜合以上的觀察，我們認為在旋轉塗佈的過程中，隨著溶劑快速揮發，氣液介面處會有高濃度的高分子，形成一層高折率的薄層，而這一薄層大體決定了最終膜的結構。

Spin-coating is an important process in the preparation of polymer thin films for functional applications. In previous studies, the focus lies mainly in the spin-off stage where fluid flow dominates. Here we pay more attention to the possible presence of a skin layer at the air-liquid interface starting from the relatively early stage of spin-coating. The film formation process during spin-coating of poly(3-hexylthiophene) (P3HT) solutions is examined by means of normal- incidence optical reflectivity (OR) and in-situ grazing incidence small/wide-angle X-ray scattering (GISWAXS). Straight-forward analysis (assuming a single liquid layer) of OR results indicates generally that there are 3 stages in the film-forming process: (1) the spin-off or flow-dominated stage, where the film-thinning rate decreases very quickly according to the Meyerhofer equation, (2) the evaporation-dominated stage of plateaued film-thinning rate, and (3) the freezing-in stage where the film-thinning rate drops to essentially zero. More sophisticated analysis (allowing for multi-layer stratification) suggests the emergence of a thin (ca. 30 nm in thickness) “epidermis” layer of high refractive index at the air/film surface during transition toward evaporation-dominated stage, which coincides approximately with the GIWAXS-detected emergence of P3HT crystallites. The GIWAXS results further indicate that both the relative crystallinity and crystallite size quickly reach saturated values and show only minor changes during the subsequent evaporation-dominated and freezing-in stages. Concurrent GISAXS results indicate the presence of oblate domains with equatorial diameter ≈ 200 nm and polar diameter ≈ 10 nm, within which P3HT crystallites presumably reside. The number of these oblate domains in the skin layer increases moderately with time before entering the freezing-in stage, but the size remains essentially the same.

TABLE OF CONTENTS
ABSTRACT I
LIST OF FIGURES V
LIST OF TABLES VI
1. Introduction 1
1.1 Background 1
1.2 Objectives and approach 2
2. Experimental details 2
3. Data analysis 3
3.1 Normal- incidence optical reflectivity spectroscopy 3
3.2 GISAXS and GIWAXS analysis 4
4. Results and Discussion 4
4.1 Evolution of thin film morphology and surface layering 4
4.2 Structural developments and polymer crystallization 8
4.3 Combination of X-ray scattering and optical reflectance 15
5. Conclusion 17
References 18
Appendix A. Film layer fitting of spin rate 1100 rpm with different models 20
Appendix B. Analysis of GISAXS/GIWAXS of 1100 rpm for bulk layer and surface layer. 21
Appendix C. Analysis of film layer at spin rate 800 rpm and 1500 rpm 23
Appendix D. Analysis of GISAXS/GIWAXS at spin rate 800 rpm and 1500 rpm. 25
LIST OF FIGURES
Figure 1-1. Time-dependent thickness of volatile fluid films during spinning at 2000 rpm.4 2
Figure 4-1. Evolution of (a) film thickness, (b) thinning-rate and (c) the corresponding Meyerhofer plot during spin-casting of a P3HT/CB solution at 1100 rpm. 6
Figure 4-2. Fitting results of optical interferograms collected at (a) t = 3.0 s, (b) t = 5.1 s, (c) t = 6.5 s, and (d) t = 8.0 s during spin-coating at 1100 rpm. 6
Figure 4-3. Schematic illustration for the film formation process during spin-coating at 1100 rpm: (a) t = 3.0 s, (b) t = 5.1 s, (c) t = 6.5 s, and (d) t = 8.0 s. 7
Figure 4-4. Evolution of film formation at spin rate 1100 rpm. 7
Figure 4-5. Representative 2D (a) GIWAXS and (b) GISAXS patterns simultaneously collected during spin-coating (at 1100 rpm) of a freshly prepared P3HT solution. 10
Figure 4- 6. Time-resolved GIWAXS profiles recorded during spin-coating of P3HT at 1100 rpm. 10
Figure 4-7. Demonstration of peak deconvolutio in GIWAXS 1D profile of 1100 rpm at 16 s. 11
Figure 4-8. (a) Crystallite size calculated from FWHM using Scherrer’s equation. (b) Development of the (100) reflection and (200) reflection from P3HT crystallite during spin-coating. (c) The crystal’s lattice spacing of the (100) P3HT peak calculated by the q position. 11
Figure 4-9. Integrated GISAXS profiles during spin-coating of a freshly prepared P3HT solution at 1100 rpm. 12
Figure 4-10. Demonstration of GISAXS (horizontal slicing of GISAXS data at qz = 0.5 nm−1) fitting by spheroid model, when at (a) 4.5 s, (b) 6.4 s and (c) 16.0 s. 13
Figure 4-11. Parameters obtained from modeling the horizontal GISAXS cuts. (a) Evolution of the polar diameter , (b) the polar diameter (c) and the inter-particle distance of oblate domains. 14
Figure 4-12. (a) A representative 2D GISAXS pattern (b) and the corresponding 2D fitGISAXS simulation of the cast film at t = 4.8 s. 14
Figure 4-13. (a) Plots of I(q)q2 v.s. qy obtained from the SAXS data (b) Scattering invariant Qinv (integrated from qy = 0.017 to 0.1 nm-1) for the P3HT recorded during spin-coating. 14
Figure 4-14. Schematic of the structure development with time obtain from the GISWAXS and optical interferometry. (a) Flow-dominated stage, (b) the beginning of evaporation-dominated stage, (c) the end of evaporation-dominated stage and (d) final film stage. 16

Figure A1. Fitting results of optical interferograms using (a) one layer model with layer gradient and (b) one layer model without layer gradient at t = 3.0 s, (c) two layers model at t = 5.1 s and (d) two layers model at t = 6.5 s during spin-coating at 1100 rpm. 20
Figure B1. Representative (a) GIWAXS and (b) GISAXS profiles recorded at 4.8 s, 6.7s and 9.9 s, respectively. 21
Figure B2. Analysis of GIWAXS for bulk layer (θi = 0.2°) and Surface layer (θi = 0.12°). (a) Development of the (100) reflection and (200) reflection from P3HT crystallite during spin-coating. (b) Crystallite size calculated from FWHM using Scherrer’s equation. 22
Figure C1. Evolution of (a) film thickness, (b) thinning rate, and (c) the corresponding Meyerhofer plot for spin-coating of the P3HT/CB solution at 800 rpm. 23
Figure C2. Evolution of (a) film thickness, (b) thinning rate, and (c) the corresponding Meyerhofer plot for spin-coating of the P3HT/CB solution at at 1500 rpm. 24
Figure C3. Stratified film structure during spin-coating at (a) 800 and (b) 1500 rpm. 24
Figure D1. GISAXS patterns collected in the freezing-in stage at (a) 800 and (b) 1500 rpm. 25
Figure D2. Integrated GISAXS profiles during spin-coating of a freshly prepared P3HT solution at (a) 800 and (b) 1500 rpm. 25
Figure D3. Time-resolved GIWAXS profiles recorded during spin-coating of P3HT at (a) 800 and (b) 1500 rpm. 25
Figure D4. (a) Crystallite size calculated from FWHM using Scherrer’s equation. (b) Intensity development of the (100) and (200) reflections from P3HT crystallites during spin-coating at different spin rates. 26


LIST OF TABLES
Table 4-1. Fittings parameters used of the UV-Vis reflectance spectra. 8
Table 4-2. Fitting parameters for scatters of layers in GISAXS simulation, according to the stratified structures revealed from optical reflectance results. The incident angle is 0.120 17
Table A1. Fittings parameters used of the UV-Vis reflectance spectra of 1100 rpm. 22

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