Progress in Polymer Science 37 (2012) 1192–1264 Contents lists available at SciVerse ScienceDirect Progress in Polymer Science j ournal homepage: www.elsevier.com/locate/ppolysci Polyfluorene-based semiconductors combined with various periodic table elements for organic electronics ∗ Ling-Hai Xie, Cheng-Rong Yin, Wen-Yong Lai, Qu-Li Fan, Wei Huang Key Laboratory for Organic Electronics & Information Displays (KLOEID) and Institute of Advanced Materials (IAM), Nanjing University of Posts & Telecommunications (NUPT), Nanjing 210046, China a r t i c l e i n f o a b s t r a c t Article history: Polyfluorenes have emerged as versatile semiconducting materials with applications in Received 12 April 2011 various polymer optoelectronic devices, such as light-emitting devices, lasers, solar cells, Received in revised form 8 February 2012 memories, field-effect transistors and sensors. Organic syntheses and polymerizations Accepted 10 February 2012 allow for the powerful introduction of various periodic table elements and their build- Available online 16 February 2012 ing blocks into ␲-conjugated polymers to meet the requirements of organic devices. In this review, a soccer-team-like framework with 11 nodes is initially proposed to illus- Keywords: trate the structure–property relationships at three levels: chain structures, thin films ␲-Conjugated polymers and devices. Second, the modelling of hydrocarbon polyfluorenes (CPFs) is summarized Band-gap engineering Light-emitting diodes within the framework of a four-element design principle, in which we have highlighted Photovoltaic cell polymorphic poly(9,9-dialkylfluorene)s with unique supramolecular interactions, various Field-effect transistors hydrocarbon-based monomers with different electronic structures, functional bulky groups Memories with steric hindrance effects and ladder-type, kinked, hyperbranched and dendritic confor- mations. Finally, the detailed electronic structure designs of main-chain-type heteroatomic copolyfluorenes (HPFs) and metallopolyfluorenes (MPFs) are described in the third and fourth sections. Supramolecular, nano and soft semiconductors are the future of polyfluo- renes in the fields of optoelectronics, spintronics and electromechanics. © 2012 Elsevier Ltd. All rights reserved. Contents 1. Introduction . 1194 1.1. Background and scope . 1194 1.2. Basic knowledge and principles . 1195 1.2.1. Performance and stability of polymer devices . 1196 1.2.2. Optoelectronic property and morphology of semiconducting polymer films. 1197 1.2.3. Four-element design of semiconducting polymers . 1199 2. Hydrocarbon polyfluorenes (CPFs) . 1202 2.1. Poly(9,9-dialkylfluorene)s (PDAFs) . 1202 ␲ 2.2. Polyfluorenes with hydrocarbon-based -conjugated monomers . 1204 2.3. Polyfluorenes substituted with various bulky groups . 1206 2.4. Fused and ladder-type polyfluorenes . 1207 2.5. Polyfluorenes with kinked conformations. 1208 2.6. Hyperbranched and dendritic polyfluorenes . 1209 ∗ Corresponding author. Tel.: +86 25 8586 6008; fax: +86 25 8586 6999. E-mail address: [email protected] (W. Huang). 0079-6700/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.progpolymsci.2012.02.003 L.-H. Xie et al. / Progress in Polymer Science 37 (2012) 1192–1264 1193 3. ␲-Conjugated heteroatomic copolyfluorenes (HPFs) . 1210 3.1. Copolyfluorenes containing heterocycles in 16th group . 1210 3.1.1. Copolyfluorenes containing oxygen heterocycles . 1211 3.1.2. Copolyfluorenes containing sulphur heterocycles. 1212 3.1.3. Copolyfluorenes containing selenium heterocycles . 1217 3.2. Copolyfluorenes containing heterocycles in 15th group . 1217 3.2.1. Copolyfluorenes containing nitrogen heterocycles . 1218 3.2.2. Copolyfluorenes containing phosphorus heterocycles . 1229 3.3. Copolyfluorenes containing heterocycles in 14th group .... 1231 3.4. Copolyfluorenes containing heterocycles in 13th group ... 1232 4. Metallopolyfluorenes (MPFs) . 1233 4.1. Copolyfluorenes containing main-group metals . 1234 4.2. Copolyfluorenes containing transition metals. 1235 4.2.1. Copolyfluorenes containing Zn(II) complexes . 1235 4.2.2. Copolyfluorenes containing Pt(II) complexes. 1237 4.2.3. Copolyfluorenes containing Ir(III) complexes . 1237 4.2.4. Copolyfluorenes containing Hg, Fe, Ru, Os, Re, or Zr complexes . 1242 4.3. Copolyfluorenes containing rare-earth metals . 1245 4.3.1. Outlook . 1248 Acknowledgements . 1248 References . 1248 Nomenclature MLCT metal-to-ligand charge transfer AFM atomic force microscopy MPFs metallopolyfluorenes BT benzothiadiazole NIR near-infrared region BHJ bulk heterojunction NTSC National Television System Committee Cz carbazole OXD 1,3,4-oxadiazole CD circular dichroism PC71BM phenyl-C71-butyric acid methyl ester CIE Commission Internationale de l’Éclairage PCBM (6,6)-phenyl C61-butyric acid methyl ester CV cyclic voltammetry PCE power conversion efficiencies CPFs hydrocarbon polyfluorenes PEDOT:PSS poly(3,4-ethylenedioxythiophene): D–A donor–acceptor poly(styrenesulphonate) DRAM dynamic random-access memory PF6 poly(9,9-dihexylfluorene) DSC differential scanning calorimetry PF2/6 poly(9,9-di(2-ethylhexyl)fluorene) DTBT 4,7-di-2-thienyl-2,1,3-benzothiadiazole PFO poly(2,7-(9,9-dioctylfluorene)) DTTP 5,7-dithien-2-yl-thieno[3,4-b]pyrazine PFs polyfluorenes EA electronic affinity PL photoluminescence EL electroluminescence PLEDs polymer light-emitting devices ET energy transfer PSCs polymer solar cells EQE external quantum efficiency QE quantum efficiency FET field-effect transistor RGB red, green and blue FF fill factor SAM self-assembled monolayer FRET Förster resonance energy transfer SAXS small-angle X-ray scattering HOMO highest occupied molecular orbital SEM scanning electron microscope HPFs heteroatomic copolyfluorenes TEM transmission electron microscopy LUMO lowest unoccupied molecular orbital TFTs thin-film transistors IP ionization potential TGA thermogravimetric analysis ISC intersystem crossing TOF time-of-flight ITO indium tin oxide UPS ultraviolet photoelectron spectrum I–V–L current–voltage–luminance WOLEDs white organic light-emitting devices LC liquid crystal UV–vis ultraviolet-visible LE luminance efficiency WORM write-once/read-many-times LECs light-emitting electrochemical cells WRER write-read-erase-reread LEPs light-emitting polymers XRD X-ray diffraction 1194 L.-H. Xie et al. / Progress in Polymer Science 37 (2012) 1192–1264 1. Introduction groups [59,60], including those of Bazan [61–63], Huang [64–69], Liu [70,71] and others [72–74]. Furthermore, 1.1. Background and scope ionic-functionalized PFs have become next-generation electron-injection or electron-extraction layers for poly- Since poly(p-phenylenevinylene) (PPV)-based polymer mer devices such as light-emitting electrochemical cells light-emitting diodes (PLEDs) were reported by Friend (LECs), PLEDs and solar cells. Cao and coworkers [75–79], in 1990 [1], polymer semiconductors and devices [2] Bazan and coworkers [80–82], and other groups [83–85] have attracted scientific and industrial interest as plastic have performed elegant research in this respect. electronic candidates for the advancement of informa- Recently, copolyfluorenes with wide-absorption ranges tion technology and the resolution of energy issues. have become attractive due to their potential applications This reflects several advantages offered by polymer-based in bulk heterojunction (BHJ) polymer solar cells (PSCs) electonics over their silicon-based counterparts, includ- by the Inganas et al. [86] and Chen and Cao [87]. High- ing light weight, low cost, large area and flexibility mobility PFs have also been applied in polymer field-effect [3,4]. To date, polymer semiconductors have been exten- transistors (FETs) by several groups [88–91]. For exam- sively and intensively investigated [5,6]; these systems ple, Sirringhaus et al. reported active-matrix displays made ␲ include -conjugated poly(p-phenylenevinylenes) (PPVs) using printed polymer thin-film transistors (TFTs).