溶液法製備氧化鋅添加聚乙烯亞胺為電子傳輸層於異質介面共軛高分子/碳球與小分子/碳球混摻塊狀高分子之高效率有機太陽能元件性質之影響

Abstract

在這論文研究中，我們使用聚乙烯亞胺(PEI)摻雜於以溶膠-凝膠處理的氧化鋅複合物薄膜中，作為有效的電子傳輸層（ETL）用於促進在反式聚合物太陽能電池中電子的萃取。利用紫外線光電子能譜，同步加速器同步輻射掠入射小角度X射線散射和穿透式電子顯微鏡，我們可觀察到ZnO:PEI複合薄膜經過不同的PEI含量至7 wt%能明顯調整導帶範圍從4.32到4.0 eV和氧化鋅薄膜結構的規則可提升垂直於ITO電極，特別是添加7wt％的PEI，促進電子垂直傳遞。並且我們製備兩種不同塊狀異質系統的太陽能電池元件以P3HT:PC61BM和PBDTTBO:PC71BM為主動層，以ZnO:PEI為電子傳輸層。當使用ZnO:PEI（93:7，w/w）作為的電子傳輸層，P3HT:PC61BM（1:1，w/w）轉換效率從原始ZnO最為電子傳輸層的3.7％值提高到4.6％，相對有24%的提升。以PBDTTBO：PC71BM（1:2，w/w）為相同電子傳輸層中PEI含量的元件，轉換效率從原始ZnO最為電子傳輸層的7.3％值提高到8.7％，相對增加20％。因此，以ZnO:PEI為複合薄膜可有效的做為有機太陽能電池內的電子傳輸層。除了把ZnO:PEI為複合薄膜及高分子做為太陽能元件，我們還研究以相同的電子傳輸層並以小分子中添加聚苯乙烯-聚乙二醇(PS-b-PEO)為主動層的太陽能元件。嵌段共聚物具有自組裝成有序結構，具有10至100奈米量級的特徵尺寸；我們採用以塊狀低分子量兩嵌段共聚物PS-b-PEO，具有不同極性的特點，能與小分子和富勒烯的相互作用及在溶液過程中調整塊狀異質結構中相分離的程度。我們添加少量奈米結構的聚苯乙烯-聚乙二醇於p-DTS(FBTTh2)2和PC71BM主動層中，能為太陽能電池中優化表面形態因此增強了元件功率轉換效率。我們使用同步加速器光源低掠角入射廣角X射線散射，原子力顯微鏡和穿透式電子顯微鏡來探討和解析所得的小分子塊狀異質結構薄膜形態並了解共聚物PS-b-PEO在小分子元件在的效率影響。元件以p-DTS(FBTTh2)2和PC71BM（1.5:1, w/w）為主動層摻入共聚物PS-b-PEO的0.5wt％，並以1,8—diiodooctane為添加劑且不經任何退火處理，轉換效率為7.3％, 與控制組比較轉換效率僅2.1％，相對增加了2.5倍。因此，在小分子主動層中摻入奈米結構化的嵌段共聚物能有效調整小分子主動層的形態以及增強的元件效率。

Bulk heterojunction organic solar cells (OSCs) based on blends of conjugated polymers or small molecules and fullerene derivatives have been extensively studied over the past few years because of their inexpensive, flexibility, renewability, and large-area processing. In traditional OSCs devices, the indium-tin oxide (ITO) appears as transparent anode normally, and poly(3,4-ethylenedioxythioph ene):poly(styrene-sulfonate) (PEDOT:PSS) is often used as anode interfacial layer to modify the morphology of ITO, further the work function of anode and ensure Ohmic contact. However, the acidic PEDOT:PSS may rust the ITO anode and cause the diffusion of indium into the active layer and such that the degradation of OSCs performance. Therefore, an inverted architecture can avoid the negative influence of PEDOT:PSS on the ITO surface and increase the absorption and stability of the OSC devices. In the first part study, we employed polyethyleneimine-doped sol–gel-processed zinc oxide composites (ZnO:PEI) as efficient electron transport layers (ETL) for facilitating electron extraction in inverted polymer solar cells. Using ultraviolet photoelectron spectroscopy, synchrotron grazing-incidence small-angle X-ray scattering and transmission electron microscopy, we observed that ZnO:PEI composite films’ energy bands could be tuned considerably by varying the content of PEI up to 7wt%—the conduction band ranged from 4.32 to 4.0 eV—and the structural order of ZnO in the ZnO:PEI thin films would be enhanced to align perpendicular to the ITO electrode, particularly at 7 wt% PEI, facilitating electron transport vertically. We then prepared two types of bulk heterojunction systems—based on poly(3-hexylthiophene) (P3HT):phenyl-C61-butryric acid methyl ester (PC61BM) and benzo[1,2-b:4,5-b´]dithiophene-thiophene-2,1,3-benzooxadiazole (PBDTTBO):phenyl -C71-butryric acid methyl ester (PC71BM)—that incorporated the ZnO:PEI composite layers. When using a composite of ZnO:PEI (93:7, w/w) as the ETL, the power conversion efficiency (PCE) of the P3HT:PC61BM (1:1, w/w) device improved to 4.6% from a value of 3.7% for the corresponding device that incorporated pristine ZnO as the ETL—a relative increase of 24%. For the PBDTTBO:PC71BM (1:2, w/w) device featuring the same amount of PEI blended in the ETL, the PCE improved to 8.7% from a value of 7.3% for the corresponding device that featured pure ZnO as its ETL—a relative increase of 20%. Accordingly, ZnO:PEI composites can be effective ETLs within organic photovoltaics. Then for the second part study, we took advantage of the different polarities of the blocks of a low-molecular-wieght diblock copolymer polystyrene-b- poly(ethylene oxide) (PS-b-PEO) that interact differentially with small molecules and fullerenes to tune the extent of the phase separation in the solution-processed small-molecule bulk-heterojunction (SMBHJ) solar cells. We incorporated small amounts of a nanostructured PS-b-PEO to solar cells’ active layers featuring p-DTS(FBTTh2)2 and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) for optimizing morphology and thus enhancing devices’ power conversion efficiency. For understanding the effect of PS-b-PEO on devices’ performances, we used synchrotron grazing-incidence wide-angle X-ray scattering, atomic force microscopy (AFM) and transmission electron microscopy (TEM) to probe and to decipher the morphologies of the resulting SMBHJ thin films. Without undergoing any annealing process, a device with an active layer of p-DTS(FBTTh2)2:PC71BM (1.5:1, w:w) that incorporated 0.5 wt % of PS-b-PEO and was processed with 1,8-diiodooctanesolvent additive displayed a power conversion efficiency (PCE) of 7.3%, a relative increase of 2.5 times as compared to the PCE of 2.1% for the control device featuring only p-DTS(FBTTh2)2 and PC71BM. Thus, incorporating this nanostructured block copolymer in the active layer allowed effective tuning of the small molecule active layer morphology and resulted in enhanced device efficiency.