Multiple Functionalities of Polyfluorene Grafted with Metal Ion-Intercalated Crown Ether as an Electron Transport Layer for Bulk-Heterojunction Polymer Solar Cells: Optical Interference, Hole Blocking

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• 作者：Sih-Hao Liao ; Yi-Lun Li ; Tzu-Hao Jen ; Yu-Shan Cheng ; Show-An Chen
• 刊名：The Journal of the American Chemical Society
• 出版年：2012
• 出版时间：September 5, 2012
• 年：2012
• 卷：134
• 期：35
• 页码：14271-14274
• 全文大小：230K
• 年卷期：v.134,no.35(September 5, 2012)
• ISSN：1520-5126

文摘

We present a novel electron transport (ET) polymer composed of polyfluorene grafted with a K⁺-intercalated crown ether involving six oxygen atoms (PFCn6:K⁺) for bulk-heterojunction polymer solar cells (PSCs) with regioregular poly(3-hexylthiophene) (P3HT) as the donor and indene鈥揅₆₀ bisadduct (ICBA) or indene鈥揫6,6]-phenyl-C₆₁-butyric acid methyl ester (IPCBM) as the acceptor in the active layer and with Al or Ca/Al as the cathode. A remarkable improvement in the power conversion efficiency (PCE) (measured in air) was observed upon insertion of this ET layer, which increased the PCE from 5.78 to 7.5% for a PSC with ICBA and Ca/Al (5.53 to 6.63% with IPCBM) and from 3.87 to 6.88% for a PSC with ICBA and Al (3.06 to 6.21% with IPCBM). This ET layer provides multiple functionalities: (1) it generates an optical interference effect for redistribution of light intensity as an optical spacer; (2) it blocks electron鈥揾ole recombination at the interface with the cathode; (3) it forms an interfacial dipole that promotes the vacuum level of the cathode metal; and (4) it enhances electron conduction, as evidenced by (1) the increase in total absorption of 1:1 w/w P3HT:ICBA by a factor of 1.3; (2) the reduction in the hole-only current density profile by a factor of 3.3 at 2.0 脳 10⁵ V/cm; (3) the decrease of 0.81 eV in the work function of Al from 4.28 to 3.47 eV, as determined by UV photoelectron spectroscopy; and (4) the decrease in the series resistance of PSCs with ICBA and Al by a factor of 4.5, as determined by the current鈥搗oltage characteristic under dark conditions; respectively. The PSC of 7.5% is the highest among the reported values for PSC systems with the simplest donor polymer, P3HT.