使用新穎的共軛高分子PTB7-Th與PC71BM所組成的活性層已經被證實其有機太陽能電池的光電轉換效率有顯著的提升，但是使轉換效率提升的原因還尚未釐清。我們團隊利用互補式的X光及中子反射法，輔以掠角小角度/廣角度散射儀以及原子力顯微鏡的測量，解析出使用氯苯溶液中不同添加劑 (DIO) 含量下所製成的主動層薄膜之結構特徵。對於無添加劑所製成的主動層薄膜中，薄膜含有一層富含PTB7-Th的表面層且有空洞 (約10 %的孔隙率) 存在於基材的介面中。在富含PTB7-Th的表面層底下，有大尺度的PC71BM扁橢狀聚集 (2A約18 nm, 2B約160 nm) 以及小尺度的PC71BM聚集 (2A約5 nm, 2B 約23 nm)。溶液中含有少量的DIO (最多3%)， 不僅消除了富含PTB7-Th的表面層與靠近基材介面的孔洞，而且抑制PC71BM生成大尺度的聚集而有利於形成碎形結構 (碎形維度約2.2)。經由DIO修飾之後PTB7-Th (100) 結晶面的相對強度也提升了。這個活性層結構的均勻性提升能夠增加正向電極的高分子太陽能電池光電轉換效率。
在反式的太陽能電池中，ZnO作為電子傳輸層，但是具有孔洞。由於這些孔洞，在活性層塗佈的過程中PTB7-Th與PC71BM會滲入基材內。因此我們採用異常散射來解析在ZnO基材中的4成份的成份分布情況。根據這個新的方法，發現PC71BM在ZnO基材中可以滲透的較PTB7-Th深。結合以上的結果，我們把反式太陽能電池的較高光電轉換效率歸因於輕微地PTB7-Th富有的表面層提供較好的電洞傳遞以及在ZnO基材中PC71BM的滲透增加電子傳遞的能力。

Use of composite active layers comprising a novel conjugated polymer PTB7-Th and modified C70 (PC71BM) has been shown to give significantly improved power conversion efficiency (PCE) of organic solar cells, but the corresponding reason behind this improvement remains unclear. Here we utilize the inherent contrast difference in X-ray and neutron reflectivity, along with the measurement of simultaneous grazing incident small/wide-angle X-ray scattering and atomic force microscopy to reveal structural characteristics of blend films spin-cast from chlorobenzene solutions containing different levels of 1,8-di-iodooctane (DIO). Films spin-cast from non-DIO solutions have a surface layer enriched in PTB7-Th while there are voids (translating to ca. 10% porosity) near the substrate interface. Under the polymer-rich skin, there are large PC71BM-rich oblate nanodomains (with equatorial diameter 2B ≈ 160 nm and polar diameter 2A ≈ 18 nm) among smaller nanodomains (with 2B ≈ 23 nm and 2A ≈ 5 nm). Minor presence of DIO (up to 3%) in the spin solution not only eliminates the polymer-rich skin layer and the porosity near the substrate interface, but also suppresses the formation of PC71BM-rich large nanodomains in favor of fractal aggregation (with fractal dimension Df ≈ 2.2) of the small PC71BM-rich ellipsoids. The relative intensity of the (100) reflection of PTB7-Th crystallites also increased via DIO-modification. This improved homogeneity in the active-layer structure results in enhanced power-conversion efficiency for polymer solar cells of conventional design.
In inverted-type solar cells, ZnO serves as electron transport layer, but with porosity. Due to these pores, the PTB7-Th and PC71BM may penetrate into these substrates during the coating process of active layer. We have therefore adopted anomalous scattering to solve for the 4-component composition profile in the ZnO substrate layer. Based on this new procedure, PC71BM was found to penetrate deeper into the ZnO substrate than PTB7-Th. Combining the results above, we attribute the higher PCE of inverted-type solar cells to the presence of a PTB7-Th-rich surface layer for better hole transport and the penetration of PC71BM into the ZnO substrate for enhanced electron transport.

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