Huang Ya-shih, Westenhoff Sebastian, Avilov Igor, Sreearunothai Paiboon, Hodgkiss Justin M, Deleener Caroline, Friend Richard H, Beljonne David
Cavendish Laboratory, University of Cambridge, J J Thomson Avenue, Cambridge, CB3 0HE, UK.
Nat Mater. 2008 Jun;7(6):483-9. doi: 10.1038/nmat2182. Epub 2008 Apr 27.
Heterojunctions between organic semiconductors are central to the operation of light-emitting and photovoltaic diodes, providing respectively for electron-hole capture and separation. However, relatively little is known about the character of electronic excitations stable at the heterojunction. We have developed molecular models to study such interfacial excited electronic excitations that form at the heterojunction between model polymer donor and polymer acceptor systems: poly(9,9-dioctylfluorene-co-bis-N,N-(4-butylphenyl)-bis-N,N-phenyl-1,4-phenylenediamine) (PFB) with poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT), and poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine) (TFB) with F8BT. We find that for stable ground-state geometries the excited state has a strong charge-transfer character. Furthermore, when partly covalent, modelled radiative lifetimes (approximately 10(-7) s) and off-chain axis polarization (30 degrees) match observed 'exciplex' emission. Additionally for the PFB:F8BT blend, geometries with fully ionic character are also found, thus accounting for the low electroluminescence efficiency of this system.
有机半导体之间的异质结是发光二极管和光伏二极管运行的核心,分别用于电子 - 空穴的捕获和分离。然而,对于在异质结处稳定存在的电子激发的特性,人们了解得相对较少。我们已经开发了分子模型来研究在模型聚合物供体和聚合物受体系统之间的异质结处形成的这种界面激发电子激发:聚(9,9 - 二辛基芴 - 共 - 双 - N,N - (4 - 丁基苯基) - 双 - N,N - 苯基 - 1,4 - 苯二胺)(PFB)与聚(9,9 - 二辛基芴 - 共 - 苯并噻二唑)(F8BT),以及聚(9,9 - 二辛基芴 - 共 - N - (4 - 丁基苯基)二苯胺)(TFB)与F8BT。我们发现,对于稳定的基态几何结构,激发态具有很强的电荷转移特性。此外,当部分为共价键时,模拟的辐射寿命(约10^(-7) s)和离链轴极化(30度)与观察到的“激基复合物”发射相匹配。另外,对于PFB:F8BT共混物,还发现了具有完全离子特性的几何结构,从而解释了该系统的低电致发光效率。