局部表面電漿，添加劑與不同溶劑對塊材異質界面高分子/富勒烯碳球太陽能電池主動層光吸收與形貌之影響

Abstract

高分子太陽能電池可以由各種不同的光電性質的材料以及多樣化的元件製程來製造。使之具備獨特與多功能性的外形和功能，這將使性能優化以及未來商品化。主動層的形貌與元件製程之間有相當重要的關聯性，因此，使用新的共軛高分子和碳球衍生物的主動層的形貌一直是許多研究者關注的對象。金屬奈米粒子有著區域表面電漿共振（LSPR）的光學特性。這種現象導致在散射電磁波的橫截面中光吸收的增強，以及一個顯著增強的高分子太陽能電池的光電轉換效率。高分子/碳球太陽能電池的能量轉換效率是極其依賴於它們的主動層，其通常經由溶液來製造。由溶液到成膜的過程可使主動層中的高分子產生結晶，這依然是在該領域的重大挑戰之一。同時，主動層的形貌會在一定程度上受到改變化學成分，所用的溶劑，以及後期處理條件這些參數的影響，而這些尚待了解。使用“添加劑”，以控制主動層的形態是用於優化異質接面元件的性能最簡單和最有效的方法之一。光電轉換效率會被高分子結晶方向所影響，相對於底座表面而言，方向為側面或正面朝上，亦與主動層中碎片形狀的PC71BM團簇大小相關。 因此首先，我們結合將金奈米點熱蒸鍍於主動層上以及嵌入八面體之金奈米粒子於電洞傳輸層中的雙層區域表面等離子共振結構，將其應用於聚噻吩共軛高分子：[6,6]-苯基C61丁酸甲酯(P3HT:PC61BM)之高分子太陽電池來增加元件效率。此雙層區域表面等離子共振結構使P3HT:PC61BM元件之光電轉換效率增加了20%的光電轉換效率。 接下來，利用同步輻射加速器的同步小角/廣角X-射線散射(GISAXS / GIWAXS)，我們已闡明了分層結構轉變的複雜機制，以PBTTPD/ PC71BM加入溶劑添加劑1,6 - diiodohexane（DIH）後，從溶液到固態膜過程中高分子結晶性的變化。我們發現，在從90 ℃冷卻至室溫的過程中，在數百秒內，PBTTPD在溶液中形成了棒狀的結構，並可能發展成高分子結晶的種子。同時， PBTTPD網絡結構的大小在高分子/碳球的溶液中的體積減小，變得更加緊湊，並且在降低溫度後，富含PC71BM結構之區域增加;而在加入DIH添加劑後，這些在溶液中的變化量大幅減少，且成膜後高分子的結晶度和碳球的堆疊均有所增強。我們的研究結果提供了高分子/碳球的結構發展機制，並進一步了解從液態到固態的變化，以及添加劑的主要功能。 其次，(一)使用同步輻射加速器的同步小角/廣角X-射線散射分析利用不同製程溶劑對共軛高分子(PBTC12TPD)的結晶與富勒烯碳球衍生物(PC61BM和ThC61BM)聚集團簇大小之影響；和(二)穿透式電子顯微鏡結合電子能量損失能譜儀分析不同溶劑製程所製造出的元件橫截面碳元素組成分佈，藉此了解元件垂直方向中，共軛高分子和富勒烯碳球自我分佈趨勢。我們發現，在元件製程中，高分子的結晶度以及富勒烯碳球的分佈大小嚴重依賴於所使用的溶劑對高分子的溶解度，這是因為一般情況下碳球在溶劑中的溶解度要比高分子好的多。 最後，我們採用1-氯化萘（CN）和1,8 - 二碘辛烷（DIO）作為雙添加劑並專注在兩者的濃度比例對高分子太陽電池效率的影響，並以此調整高分子結晶面的方向之比例，以及富勒烯碳球的團簇大小，以PBTC12TPD/PC71BM為主動層(1:1.5)加入0.5% DIO和1% CN的雙添加劑可使元件效率從4.9%提升至至6.8%，相對未使用雙添加劑之元件增加了40%。

Polymer solar cells can be fabricated from a wide range of materials with different aesthetic and optoelectronic properties by a multiple set of processes. This results in a unique versatility in device form factor and functionality, which will enable performance optimization and commercialization. The relationship between process and morphology of device active layer is unique and multiple, therefore, controlling the active layer morphology with new conjugated polymer and fullerene derivatives has been a subject of attention for many researchers. The signature optical property of noble metal nanoparticles (NPs) is their localized surface plasmon resonance (LSPR). This phenomenon leads to enhanced light absorption and scattering cross sections for electromagnetic waves, as well as a strongly enhanced of the power conversion efficiency (PCE) of polymer solar cells. The PCE of polymer/fullerene solar cells are critically dependent on the morphologies of their active layers, which are typically processed from solution. The structural transition from solutions to solid films of the crystalline polymer is one of the grand challenges in the field. Simultaneously, the morphology of the active layer can be influenced to some extent by varying such parameters as the chemical composition, the solvent used, and the postproduction treatment conditions, but often it is not understood a priori. The use of a solvent additive to control the morphology of the active layer is one of the simplest and most effective methods for optimizing the performance of a BHJ device. PCE can also be significantly affected by the orientation of face- and edge-on polymer lamellar crystals, relative to the substrate surface, as well as the sizes of the fractal-like PC71BM clusters in the active layer. In the first, we investigated the effects of plasmonic resonances induced by gold nanodots (Au NDs), thermally deposited on the active layer, and octahedral gold nanoparticles (Au NPs), incorporated within the hole transport layer, on the performance of bulk heterojunction polymer solar cells (PSCs) based on poly(3-hexyl thiophene) (P3HT) and [6,6]-phenyl-C61butyric acid methyl ester (PC61BM). Thermally deposited Au-NDs and embedding Au NPs within the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) to form a dual metallic nanostructure can further enhance PCE to 4.8%—that is about 20% greater than that of the conventional P3HT:PC61BM cell. In the second, using synchrotron wide- and small-angle X-ray scattering, we have elucidated the intricate mechanism of the hierarchical structural transitions from solutions to solid films of the crystalline polymer poly[bis(dodecyl)thiophene- thieno[3,4-c]pyrrole-4,6-dione] (PBTTPD) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM), including the effect of the solvent additive 1,6-diiodohexane (DIH). We found that the local assembly of rigid-rod PBTTPD segments (ordered nano-domains) that formed in solution instantly and then relaxed within several hundred seconds upon cooling to room temperature from 90℃ could develop into seeds for subsequent crystallization of the polymer in the solid films. Concurrently, the sizes of the PBTTPD network structures in the blend solutions decreased and became more compact, and the PC71BM-rich domains increased upon decreasing the temperature; in the presence of additive DIH, these variations in the structures in solutions that were subject to the same cooling were substantially mitigated. The polymer’s crystallinity and the fullerene packing were both enhanced in the subsequent solid films that were processed involving DIH when the solvent removal process was relatively rapid. Our results provide a detailed understanding of the mechanism behind the structural development of polymer/fullerene blends upon their transitions from solution to the solid state, as well as the key functions of the additive. In the third, we used (i) synchrotron grazing-incidence small-/wide-angle X-ray scattering to elucidate the crystallinity of the polymer PBTC12TPD and the sizes of the clusters of the fullerenes PC61BM and ThC61BM and (ii) transmission electron microscopy/electron energy loss spectroscopy to decipher both horizontal and vertical distributions of fullerenes in PBTC12TPD/fullerene films processed with chloroform, chlorobenzene and dichlorobezene. We found that the crystallinity of the polymer and the sizes along with the distributions of the fullerene clusters were critically dependent on the solubility of the polymer in the processing solvent when the solubility of fullerenes is much higher than that of the polymer in the solvent. Finally, we employed 1-chloronaphthalene (CN) and 1,8-diiodooctane (DIO) as binary additives exhibiting relatively complementary preferential solubility for the crystalline conjugated polymer poly[bis(dodecyl)thiophene-dodecyl-thieno[3,4-c] pyrrole-4,6-dione] (PBTC12TPD) and the fullerene [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) in chloroform, allowing us to tune the amount of edge-on and face-on polymer lamellae and size of PC71BM clusters in the active layer in bulk heterojunction (BHJ) solar cells. The power conversion efficiency of a device incorporating an active layer of PBTC12TPD/PC71BM (1:1.5, w/w) processed with 0.5% DIO and 1% CN as additives in chloroform increased to 6.8% from a value of 4.9%, a relative increase of 40%, for the corresponding device containing the same active layer but processed without any additive.