Co-reporter:Zi Wang;Tong Wang;Haibo Wang
Advanced Materials 2014 Volume 26( Issue 26) pp:4582-4587
Publication Date(Web):
DOI:10.1002/adma.201400702
Co-reporter:Tong Wang, Donghang Yan
Advances in Colloid and Interface Science 2014 Volume 207() pp:332-346
Publication Date(Web):May 2014
DOI:10.1016/j.cis.2014.01.012
Highlights
- •
The growth behavior of rod-like molecules on SiO2 substrates was studied.
- •
The neighboring domains of monolayer coalesce well.
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The defect density of the grain boundaries can be reduced notably.
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The ultrathin films exhibit Liquid-crystal-like behavior and flexible boundary.
Co-reporter:Zi Wang, Hao Chang, Tong Wang, Haibo Wang, and Donghang Yan
The Journal of Physical Chemistry B 2014 Volume 118(Issue 15) pp:4212-4219
Publication Date(Web):March 27, 2014
DOI:10.1021/jp412310y
The heterostructure, a basic active unit applied in the device level, plays an important role in traditional inorganic optoelectronics. In the organic field, although the requirement for the heterostructure is crucial, achievement and understanding on the growth and functionality of organic heterostructure are still finite, especially for ordered crystalline organic multilayers with smooth interfaces. Here a series of highly ordered crystalline heterostructures with molecule-level smoothness were obtained from single layer to alternate multilayer with a phthalocyanine molecule and a perylene derivative. Well-defined epitaxy relationship and crystal alignment were evidenced from the atomic force microscopy (AFM), X-ray diffraction (XRD), and transmission electron microscope (TEM) results. The evolution of the films reveals that, for organic–organic alternate multilayer growth, along with the intrinsic properties of organic molecules such as the packing and preferred growth direction, the soft matter properties of organic films contribute to well-defined heteroepitaxy despite that the lattice mismatch between the two materials’ bulk phases is large. Thin film phases of the first few layers benefit the grain coalescence and thus the formation of smooth films. Potential application is implied from the heterojunctions’ good transport ability.
Co-reporter:Shiliang Ji;Haibo Wang;Tong Wang
Advanced Materials 2013 Volume 25( Issue 12) pp:1755-1760
Publication Date(Web):
DOI:10.1002/adma.201204134
Co-reporter:Shiliang Ji, Xiujin Wang, Chengfang Liu, Haibo Wang, Tong Wang, Donghang Yan
Organic Electronics 2013 Volume 14(Issue 3) pp:821-826
Publication Date(Web):March 2013
DOI:10.1016/j.orgel.2013.01.006
We reported an organic room temperature (RT) NO2 sensor based on zinc phthalocyanine (ZnPc) nanofiber network. Compared with traditional polycrystalline ZnPc film devices, the sensors with ZnPc nanofiber network as the sensitive layer exhibit much better recovery characteristics, which could almost recover without any treatments at room temperature. In ZnPc nanofiber network, ultra-thin ZnPc single-crystal fibers not only improve charge transport but also make the charge exchanging process between NO2 and sensitive materials easier. It shortens the response and recovery time and stabilizes the baseline of devices. In addition, we also optimized the sensors by varying the scale of the ZnPc nanofiber. The device performance is obviously improved when the scale of the ZnPc nanofiber becomes smaller. The device could naturally recover and the baseline achieves zero drift. It is attributed to the expansion of the ratio of surface area-to-volume (A/V).Graphical abstractHighlights► Achieve detecting NO2 at room temperature. ► Controlled scale ZnPc nanofiber network sensor. ► Reveal the law of the specific surface area in organic sensor.
Co-reporter:Chengfang Liu, Qilin Wang, Hongkun Tian, Jian Liu, Yanhou Geng, and Donghang Yan
Macromolecules 2013 Volume 46(Issue 8) pp:
Publication Date(Web):April 12, 2013
DOI:10.1021/ma400010f
Lenticular crystals of the β phase of monodisperse poly(9,9-dioctylfluorene)s (PFOs) have been prepared from o-dichlorobenzene (ODCB) solution. The diffraction analysis combined with X-ray and electron diffraction diagrams indicates that PFOs can crystallize in the orthorhombic system which have the lattice parameters of a = 1.32 nm, b = 2.10 nm, and c = 3.36 nm. In these single crystals, the backbone chains are packed parallel to the long axis of crystals. Furthermore, a variation of the annealing temperature from 90 to 130 °C demonstrates that there exists morphology and structure evolution, which has been systematically investigated by optical microscopy and electron microscopy.
Co-reporter:Chengfang Liu, Qilin Wang, Hongkun Tian, Yanhou Geng, Donghang Yan
Polymer 2013 Volume 54(Issue 9) pp:2459-2465
Publication Date(Web):19 April 2013
DOI:10.1016/j.polymer.2013.02.040
Polymer single crystals of monodisperse poly (9,9-dioctylfluorene)s (PFOs) with actual molecular weights of 6220, 12,437 and 24,874 Da corresponding to the numbers of fluorene repeating units of 16, 32 and 64, respectively, were grown from chloroform/ethanol solutions. In the single crystals, polymer chains adopt lamellar packing motif. The crystal structure determined by electron diffraction is identical for all three PFOs, and the single crystal has an orthorhombic unit cell with lattice parameters of a = 2.16 nm, b = 1.28 nm, and c = 3.36 nm. In these lamellar crystals, PFO backbones are arranged perpendicular to the lamellar surface and alkyl side chains are along the crystal-growth direction. The lamellar thickness is identical to the extended chain length of the corresponding polymer as demonstrated by atomic force microscopy (AFM) measurements. It is noteworthy to point out that F64 still maintain extended-chain packing habit even when the chain length is as long as 53 nm. Therefore, our results demonstrated that chains remain extended in this system.
Co-reporter:Chengfang Liu, Qilin Wang, Hongkun Tian, Jian Liu, Yanhou Geng, and Donghang Yan
The Journal of Physical Chemistry B 2013 Volume 117(Issue 29) pp:8880-8886
Publication Date(Web):July 2, 2013
DOI:10.1021/jp401261u
Different crystalline forms are obtained by simply manipulating the good/poor solvent ratio in mixed solvents of toluene/ethanol. Depending on different solvent ratios, poly(9,9-dioctylfluorene)s (PFOs) can generate a large palette of morphologies including lenticular crystals, fibrous crystals and rod-like crystals. In the crystallization process, polymer chains experience different kinetic pathways, yielding lenticular crystals in the toluene solution, rod-like crystals at a low toluene/ethanol ratio (1:1), and fibrous crystals at a high toluene/ethanol ratio (3:1). A combination of atomic force microscopy (AFM) and transmission electron microscopy (TEM) provides an opportunity to elucidate the distinctive molecular arrangements in these different crystals. Moreover, the influence of molecular weights on the crystallization of polymers has also been investigated in different crystals.
Co-reporter:Chengfang Liu, Aiguo Sui, Qilin Wang, Hongkun Tian, Yanhou Geng, Donghang Yan
Polymer 2013 Volume 54(Issue 13) pp:3150-3155
Publication Date(Web):7 June 2013
DOI:10.1016/j.polymer.2013.04.025
Lamellar crystals of polydisperse poly (9,9-di-n-octyl-2,7-fluorene)s were obtained from dilute solution. By means of scanning electron microscopy (SEM) and atomic force microscopy (AFM), we found that polymer chains formed lamellar single crystals through fractionated crystallization, in which components of the largest mass fraction crystallized first and remained extended in the first lamella. With the depletion of the species, other components continued the crystal growth and deposited on the already formed surface, which gave rise to the variation in lamellar thicknesses. Therefore, our study not only confirmed the feasibility of our previously crystallization mechanism of the binary mixture on the polydisperse Fn but also provided an extension of the research on the crystallization behavior.
Co-reporter:Chengfang Liu, Qilin Wang, Hongkun Tian, Jian Liu, Yanhou Geng, Donghang Yan
Polymer 2013 Volume 54(Issue 3) pp:1251-1258
Publication Date(Web):5 February 2013
DOI:10.1016/j.polymer.2012.12.054
Polymer crystals of monodisperse poly (9,9-dioctylfluorene)s (PFOs, named as Fn) on mixing both components (F16 and F64) in different ratios are grown from chloroform/ethanol solutions. In these crystals, lamellar thicknesses corresponding to relevant components can be observed by utilizing atomic force microscopy (AFM). Crystallization of these polymers is accompanied by fractionated crystallization where saturation solubility of different components remarkably affects the crystallization process. Moreover, we report on the stability of the crystal under thermal annealing and solvent annealing. The crystal is thermally stable, but can be eventually dissolved at the good solvent which takes advantages of the slow crystallization process to accomplish the process.
Co-reporter:Xiaolan Qiao, Hao Chang, Lizhen Huang, Jidong Zhang, Hongkun Tian, Yanhou Geng and Donghang Yan
Physical Chemistry Chemical Physics 2012 vol. 14(Issue 29) pp:10279-10284
Publication Date(Web):06 Jun 2012
DOI:10.1039/C2CP41248A
The growth process and phase state of 5,5′′-bis(3′-fluoro-biphenyl-4-yl)-2,2′:5′,2′′- terthiophene (m-F2BP3T) thin films were investigated by atomic force microscopy (AFM), in-plane and out-of-plane X-ray diffraction (XRD), and selected area electron diffraction (SAED). Two meso-phases (thin film phases) of m-F2BP3T films on SiO2 surface were obtained in the early stages. The m-F2BP3T films initially exhibited two-dimensional (2D) layers (≤4 ML) followed by three-dimensional (3D) island growth. The film structure evolved two thin film phases in the first four layers and the bulk phase was formed from the fifth layer, which occurred concomitantly with the change of the growth mode. Moreover, the variation of weak epitaxy growth behavior of ZnPc from 2D to 3D growth further reflects that the phase state of the first three layers is different from that of the fourth layer, in spite of ZnPc crystals showing just one orientation corresponding to commensurate epitaxy. The novel phase behavior is closely related to the synergistic effects of the outstanding soft matter properties, limited elasticity of organic molecules, and strain originating from the SiO2 substrate. This study investigates novel phase behavior in organic thin films and provides significant insight into the mechanism of the phase transition.
Co-reporter:Xiaolan Qiao, Lizhen Huang, Weichao Chen, Hao Chang, Jidong Zhang, Donghang Yan
Organic Electronics 2012 Volume 13(Issue 11) pp:2406-2411
Publication Date(Web):November 2012
DOI:10.1016/j.orgel.2012.06.035
The film morphology, structure, and electrical properties of lead phthalocyanine (PbPc) epitaxially grown on 5,5″-bis(3′-fluoro-biphenyl-4-yl)-2,2′:5′,2″-terthiophene (m-F2BP3T) inducing layer substrates were systematic investigated. The morphologies of PbPc films sensitively depend on the thickness of the inducing layer and substrate temperature. All the epitaxial PbPc films with high quality presented the triclinic form with a variation of the out-of-plane orientation. The field-effect mobility of the epitaxial PbPc films was 0.05–0.31 cm2/V s, which was significantly improved by 1–2 orders of magnitude compared to the traditional films. The evolution of the device performance is the synergistic effect of the morphology and out-of-plane orientation of the triclinic form of PbPc. The higher quality of the films and the smaller ratio of (1 0 0)/(0 0 1), the higher device performance is. A clear relationship between the morphology, structure, and the performance of epitaxial PbPc-based organic field-effect transistors was reported.Graphical abstractHighlights► High quality PbPc films with large grain size and well continuity are obtained. ► The crystalline films are composed of uniform triclinic form PbPc crystals. ► The films show the highest mobility of 0.31 cm2/V s in optimized devices.
Co-reporter:Jianbing Yang, Weichao Chen, Bo Yu, Haibo Wang, Donghang Yan
Organic Electronics 2012 Volume 13(Issue 6) pp:1018-1022
Publication Date(Web):June 2012
DOI:10.1016/j.orgel.2012.02.015
We developed an active inter-connecting layer (ICL) composed of SnCl2Pc/Al/F16CuPc/ZnPc to achieve an effective organic tandem solar cell consisting of complementary absorbing layers. This ICL provides a new function to improve the light response of the top cell to enhance current matching between bottom cell and top cell. Meanwhile, the ICL is highly transparent and has efficient charge collections to realize electric connection in series. Finally, in the tandem cell, the open-circuit voltage of 1.52 V is obtained that is the summation of the single cells (1.08 V and 0.46 V), and the power conversion efficiency of 3.21% under 100 mW/cm2 is achieved that is higher than those of the single cells.Graphical abstractHighlights► An active inter-connecting layer is presented to obtain an efficient tandem cell. ► The ICL has a new function to improve the light response of the top cell. ► The ICL is highly transparent and low resistance. ► Current matching between bottom cell and top cell has been realized.
Co-reporter:Weichao Chen, Lizhen Huang, Xiaolan Qiao, Jianbing Yang, Bo Yu, Donghang Yan
Organic Electronics 2012 Volume 13(Issue 6) pp:1086-1091
Publication Date(Web):June 2012
DOI:10.1016/j.orgel.2012.03.002
Efficient planar organic solar cells extending the response into the near-infrared (NIR) were fabricated using the highly ordered Titanyl phthalocyanines (TiOPc) films as the donor layer. This type of films obtained through the weak epitaxy growth (WEG) method presents good continuity and integrity with the low density of grain boundaries. More importantly the films own a strong absorption in the NIR (750–950 nm) and a broad absorption spectrum from 550 to 950 nm. Meanwhile the high external quantum efficiency (EQE) is obtained in the NIR with the peak value over 38% and the EQE is over 18% in the entire response range, which could benefit from the long exciton diffusion length and the high carrier mobility of the highly ordered films. Thereby the fabricated planar solar cells achieve a high short-circuit current density (Jsc) of 9.26 mA cm−2 and a power conversion efficiency (PCE) of 2.67%.Graphical abstractHighlights► The BP2T/TiOPc/C60 cells show the high EQE in the NIR with peak value over 38%. ► The cells are fabricated using the ordered TiOPc phase II films as the donor layer. ► The TiOPc films demonstrate good continuity, integrity and low grain boundaries.
Co-reporter:Xiaolan Qiao, Lizhen Huang, Jidong Zhang, Hongkun Tian, Yanhou Geng, and Donghang Yan
The Journal of Physical Chemistry B 2012 Volume 116(Issue 6) pp:1812-1818
Publication Date(Web):January 11, 2012
DOI:10.1021/jp210535q
Weak epitaxy growth (WEG) is an effective method in the preparation of high-mobility thin films of disk-like organic semiconductors. The growth behavior and quality of the epitaxial thin film are closely related to the inducing layers. Here, a series of fluorinated molecules, 5,5″-bis(3′-fluoro-biphenyl-4-yl)-2,2′:5′,2″-terthiophene (m-F2BP3T), 5,5″-bis(3′,5′-difluoro-biphenyl-4-yl)-2,2′:5′,2″-terthiophene (F4BP3T), and 5,5″-bis(4′-fluoro-biphenyl-4-yl)-2,2′:5′,2″-terthiophene (p-F2BP3T) as well as a referenced molecule 5,5″-bis(biphenyl-4-yl)-2,2′:5′,2″-terthiophene (BP3T), are introduced to serve as inducing layers for the epitaxy growth of phthalocyanine. Compared to the nonfluorinated inducing layer, the interactions between the fluorinated inducing layer and phthalocyanine might be relatively strong due to the potential existence of C–H···F weak hydrogen bonds. The growth behavior and mechanism of phthalocyanine on the fluorinated inducing layers are investigated by atomic force microscopy (AFM), grazing incidence X-ray diffraction (GIXD), selected area electron diffraction (SAED). According to the AFM and SAED, H2Pc presents a selective epitaxy growth depending on the position of fluorine: epitaxy growth on m-F2BP3T and F4BP4T, and nonepitaxy growth on p-F2BP3T. Comparison of CuPc with F16CuPc on monolayer p-F2BP3T further revealed that the uncommon nonepitaxy growth behavior of H2Pc (CuPc) on p-F2BP3T mainly originates from the enhanced interactions between the two types of molecules. As a consequence, the capability of molecules orienting themselves along the surface channel is decreased; meanwhile, the demand of the upper limit of the lattice mismatch is more rigorous for commensurate epitaxy. Finally, the oriented nucleation of H2Pc (CuPc) on monolayer p-F2BP3T is affected, and netlike crystals are formed. The sudden change of H2Pc (CuPc) from multiorientation on monolayer to just one orientation on double-layer p-F2BP3T suggests that there is a critical lattice mismatch value for commensurate epitaxy in WEG when the molecule–substrate interactions are enhanced.
Co-reporter:Lizhen Huang;Chengfang Liu;Xiaolan Qiao;Hongkun Tian;Yanhou Geng
Advanced Materials 2011 Volume 23( Issue 30) pp:3455-3459
Publication Date(Web):
DOI:10.1002/adma.201101353
Co-reporter:Xiujin Wang, Shiliang Ji, Haibo Wang, Donghang Yan
Organic Electronics 2011 Volume 12(Issue 12) pp:2230-2235
Publication Date(Web):December 2011
DOI:10.1016/j.orgel.2011.09.014
We report a heterojunction gas sensor with an enhanced relative response to nitrogen dioxide (NO2) below 5 ppm and a detection limit down to 250 ppb at room temperature. The 1.8 nm titanyl phthalocyanine (TiOPc) film as bottom layer with 1 nm hexadecafluorinated copper phthalocyanine (F16CuPc) film as top layer has constructed an ultrathin bilayer sensor device. Kelvin probe force microscopy (KPFM) results indicated that p–n heterojunction was formed at the interface. The top layer has formed local electron accumulating area and made the film more reductive to analyte. The top layer acts as extra surface active sites in addition to the grain boundaries and these heterostructures can adsorb analytes more effectively.Graphical abstractHighlights► A bilayer sensor device was fabricated and it shows an enhanced response towards NO2 compared with monolayer device. ► p–n Heterostructure was formed in bilayer and the surface potential is adjusted. ► These electron accumulating areas made the film more reductive to NO2 and made the bilayer device more sensitive.
Co-reporter:Feng Pan, Hongkun Tian, Xianrui Qian, Lizhen Huang, Yanhou Geng, Donghang Yan
Organic Electronics 2011 Volume 12(Issue 8) pp:1358-1363
Publication Date(Web):August 2011
DOI:10.1016/j.orgel.2011.05.003
A high performance VOPc thin-film transistor based on a fluorobenzene end-capped quaterthiophene as the inducing layer is fabricated by weak epitaxy growth method. The quality of epitaxial VOPc films is significantly improved. A commensurate epitaxial relationship is formed between the inducing layer and the VOPc films, leading to highly ordered VOPc films with large grains, which enhances the in-plane carrier transport. The field-effect mobility reaches up to 2.6 cm2 V−1 s−1, the threshold voltage is lower than −5 V, and the on–off current ratio is higher than 106. The device performance has no significant degradation in ambient condition for 100 days. The high-performance and the air-stable VOPc OTFTs promote the practical applications for large-area and flexible display.Graphical abstractHighlights► A high performance VOPc transistor was obtained using a new inducing layer F2-P4T. ► F2-P4T film possesses smooth surface and small lattice mismatch with VOPc, resulting in a high quality VOPc films. ► The VOPc transistors present high mobility up to 2.6 cm2/V s, and low threshold voltage. ► Less deterioration of the transistor performances was observed after 100 days stored in ambient condition.
Co-reporter:Xiujin Wang, Shiliang Ji, Haibo Wang, Donghang Yan
Sensors and Actuators B: Chemical 2011 160(1) pp: 115-120
Publication Date(Web):
DOI:10.1016/j.snb.2011.07.021
Co-reporter:Bo Yu;Lizhen Huang;Haibo Wang
Advanced Materials 2010 Volume 22( Issue 9) pp:1017-1020
Publication Date(Web):
DOI:10.1002/adma.200903023
Co-reporter:Haibo Wang and Donghang Yan
NPG Asia Materials 2010 2(2) pp:69-78
Publication Date(Web):2010-04-01
DOI:10.1038/asiamat.2010.44
A heterojunction is an interface between two semiconductor materials of differing
energy gap, and inorganic heterojunctions have been studied as the basis of
electronic devices for over half a century. Organic heterojunctions have also
been successfully applied in organic electronic devices over the past two
decades. However, a theoretical understanding comparable to that of inorganic
heterojunctions has yet to be developed for organic heterojunctions. Organic
heterojunctions have been drawing increasing attention following the discovery
of high conductivity in organic heterojunction transistors constructed with
active layers of p-type and n-type thin crystalline films. In contrast with the
depletion layers that form in inorganic heterojunctions, electron- and
hole-accumulation layers have been observed on both sides of organic
heterojunction interfaces. Heterojunction films with high conductivity have been
used as charge injection buffer layers and as a connecting unit for tandem
diodes. Ambipolar transistors and light-emitting transistors have also been
realized using organic heterojunction films as active layers. This review
highlights the organic heterojunction effect and the application of organic
heterostructures in organic field-effect transistors. The category of
heterojunction, including organic and inorganic semiconductor heterojunctions,
is given on the basis of the work function of the constituent materials, and it
is shown that a rich variety of organic heterojunctions are possible based on
the formation of molecular pairs.
Co-reporter:Lizhen Huang, Feng Zhu, Chengfang Liu, Haibo Wang, Yanhong Geng, Donghang Yan
Organic Electronics 2010 Volume 11(Issue 2) pp:195-201
Publication Date(Web):February 2010
DOI:10.1016/j.orgel.2009.10.014
High performance films of phenyl substituted perylene diimide are obtained by heteroepitaxy growth through Weak Epitaxy Growth technique. As epitaxially grown on the para-sexiphenyl (p-6P) ordered layers, the N,N′-di-phenyl perylene tetracarboxylic diimide (PTCDI-Ph) grows to form continuous and highly oriented films with large grain size, which possess low density of grain boundary and smooth surface. This quality films bring about improvement of two orders of magnitude in mobility compare to the traditional films, and present relative good air stability. Ambipolar transport behavior was also observed as tuning the thickness of p-6P.
Co-reporter:Lizhen Huang, Chengfang Liu, Bo Yu, Jidong Zhang, Yanhong Geng and Donghang Yan
The Journal of Physical Chemistry B 2010 Volume 114(Issue 14) pp:4821-4827
Publication Date(Web):March 19, 2010
DOI:10.1021/jp100095r
Evolution of BP2T films grown at the early stage was investigated using atomic force microscopy (AFM) and X-ray diffraction (XRD). The AFM results demonstrate that the BP2T grown on the SiO2 substrate transformed from a layer by layer growth to island growth when the coverage is higher than 3 ML. The out-of-plane and in-plane X-ray diffraction measurements reveal a phase transition from the thin film phase to the bulk phase suddenly occurs as the growth mode changes. A careful analysis of the structure evolution implies that not only the strain but also the soft matter property of the organic thin films are responsible for the thickness dependent evolution. Moreover, the thickness dependent structure and phase of BP2T films result in different morphologies of ZnPc grown on different layers of BP2T. The ZnPc crystals gradually changed from stripe-like to nanofiber-like, concomitantly with the epitaxy relationships from incommensurate epitaxy to commensurate epitaxy. Conversely, the diversity of ZnPc films also reflects different properties of the BP2T films with different numbers of layer, which cannot be obtained from the AFM or XRD. This study supplies a deeper insight into the thickness evolution of organic thin films and to the weak epitaxy growth.
Co-reporter:Tong Wang, Lizhen Huang, Junliang Yang, Hongkun Tian, Yanhou Geng, and Donghang Yan
The Journal of Physical Chemistry B 2010 Volume 114(Issue 49) pp:16408-16413
Publication Date(Web):November 18, 2010
DOI:10.1021/jp1058066
The growth of ultrathin films of 2,5-bis(4-1,1′:4′,1′′-terphenyl)-thiophene (3PT) and weak epitaxy growth (WEG) behavior of phthalocyanines (H2Pc and ZnPc) on 3PT ultrathin films were investigated by atomic force microscopy, X-ray diffraction (XRD), and select area electron diffraction (SAED). Domain size of the monolayer films can reach 10 μm at the substrate temperature of 190 °C. The second layer films begin to show Volmer−Weber growth mode. This growth mode transformed without a concomitant phase transition. The XRD and SAED measurements indicate the monolayer and double-layer films of 3PT have identical in-plane and out-of-plane structure. The epitaxial ZnPc films have a similar orientation or intertexture shape utilizing 3PT monolayer and double-layer films as the inducing layer. By comparison with utilizing para-sexiphenyl (p-6P) as the inducing layer, the morphology with clear borderline of epitaxial films with different orientations on joint of neighboring 3PT monolayer domains disclosed that the 3PT monolayer films have characteristics of crystal. Meanwhile the distinguishing effects of inducing layer phase state on morphology of epitaxial films were shown, respectively.
Co-reporter:Junliang Yang and Donghang Yan
Chemical Society Reviews 2009 vol. 38(Issue 9) pp:2634-2645
Publication Date(Web):27 May 2009
DOI:10.1039/B815723P
The fabrication of organic semiconductor thin films is extremely important in organic electronic devices. This tutorial review—which should particularly appeal to chemists and physicists interested in organic thin-film growth, organic electronic devices and organic semiconductor materials—summarizes the method of weak epitaxy growth (WEG) and its application in the fabrication of high quality organic semiconductor thin films. WEG achieves the thin-film fabrication of disk-like organic semiconductor molecules with highly structural order, molecular level smoothness and large size domains on amorphous substrate. The organic field-effect transistor devices based on these thin films exhibit a high charge mobility that is comparable with their corresponding single-crystal devices. Moreover, it provides a way to produce organic superlattices.
Co-reporter:Chunhong Li, Feng Pan, Xiujin Wang, Lijuan Wang, He Wang, Haibo Wang, Donghang Yan
Organic Electronics 2009 Volume 10(Issue 5) pp:948-953
Publication Date(Web):August 2009
DOI:10.1016/j.orgel.2009.05.001
Organic thin-film transistors (OTFTs) using high dielectric constant material tantalum pentoxide (Ta2O5) and benzocyclobutenone (BCBO) derivatives as double-layer insulator were fabricated. Three metals with different work function, including Al (4.3 eV), Cr (4.5 eV) and Au (5.1 eV), were employed as gate electrodes to study the correlation between work function of gate metals and hysteresis characteristics of OTFTs. The devices with low work function metal Al or Cr as gate electrode exhibited high hysteresis (about 2.5 V threshold voltage shift). However, low hysteresis (about 0.7 V threshold voltage shift) OTFTs were attained based on high work function metal Au as gate electrode. The hysteresis characteristics were studied by the repetitive gate voltage sweep of OTFTs, and capacitance–voltage (C–V) and trap loss-voltage (Gp/ω−V) measurements of metal–insulator–semiconductor (MIS) devices. It is proved that the hysteresis characteristics of OTFTs are relative to the electron injection from gate metal to Ta2O5 insulator. The electron barrier height between gate metal and Ta2O5 is enhanced by using Au as gate electrode, and then the electron injection from gate metal to Ta2O5 is reduced. Finally, low hysteresis OTFTs were fabricated using Au as gate electrode.
Co-reporter:Tong Wang, Daniel Ebeling, Junliang Yang, Chuan Du, Lifeng Chi, Harald Fuchs and Donghang Yan
The Journal of Physical Chemistry B 2009 Volume 113(Issue 8) pp:2333-2337
Publication Date(Web):January 29, 2009
DOI:10.1021/jp8080639
Weak epitaxy growth (WEG) behavior and mechanism of copper hexadecafluorophthalocyanine (F16CuPc) on p-sexiphenyl (p-6P) monolayer film were investigated by atomic force microscopy (AFM), selected area electron diffraction (SEAD), and wide-angle X-ray diffraction (WAXD). High-quality F16CuPc films with high order, large size, and molecular-level smoothness were obtained successfully by WEG method. It was identified that there exists incommensurate epitaxial relation between highly oriented F16CuPc and p-6P films. The geometrical channels of p-6P monolayer surface induce the nucleation and growth of F16CuPc molecules. Two kinds of in-plane structures, referred to as “phase I” and “phase II”, coexist in the initial few molecular layers. As thin-film thickness increases, the distance of (001) plane diminishes and phase I disappears. Furthermore, coalescence, dislocation, and high-angle grain boundary between F16CuPc neighboring domains were observed by high-resolution AFM.
Co-reporter:De Song;Haibo Wang;Feng Zhu;Junliang Yang;Hongkun Tian;Yanhou Geng
Advanced Materials 2008 Volume 20( Issue 11) pp:2142-2144
Publication Date(Web):
DOI:10.1002/adma.200702439
Co-reporter:Xiaoxia Jiang, Jiguang Dai, Haibo Wang, Donghang Yan
Thin Solid Films 2008 Volume 516(Issue 18) pp:6487-6491
Publication Date(Web):31 July 2008
DOI:10.1016/j.tsf.2008.02.026
We fabricated the interdiffused organic photovoltaic devices, which composed of poly (2-methoxy-5-(2′-ethylhexyloxy)-1, 4-phenylen-evinylene) (MEH-PPV) and buckminsterfullerene (C60), by annealing treatment. After annealing, C60 diffused into the MEH-PPV layer, in consequence, MEH-PPV/C60 interfacial area was increased and their interface became closer proximity. The results lead to reduce reverse-bias saturation current (JS), and increase the open-circuit voltage (VOC) and the short-circuit current (JSC). Moreover, the increase in conductivity of poly (3, 4-ethylenedioxythiophene)/poly (styrenesulfonate) is also responsible for the performance improvement. Consequently, the power conversion efficiency is improved from 0.17% to 0.92% combined with the all increase of JSC, VOC and fill factor.
Co-reporter:Jianwu Shi, Haibo Wang, De Song, Hongkun Tian, Yanhou Geng, Donghang Yan
Thin Solid Films 2008 Volume 516(Issue 10) pp:3270-3273
Publication Date(Web):31 March 2008
DOI:10.1016/j.tsf.2007.08.037
Ambipolar transport has been realized in organic heterojunction transistors with metal phthalocyanines, phenanthrene-based conjugated oligomers as the first semiconductors and copper-hexadecafluoro-phthalocyanine as the second semiconductor. The electron and hole mobilities of ambipolar devices with rod-like molecules were comparable to the corresponding single component devices, while the carrier mobility of ambipolar devices with disk-like molecules was much lower than the corresponding single component devices. The much difference of their device performance was attributed to the roughness of the first semiconductor films, which was original from their distinct growth habits. The flat and continuous films for the first semiconductors layer can lead to a smooth heterojunction interface, and obtained a high device performance for ambipolar organic heterojunction transistors.
Co-reporter:Tong Wang, Junliang Yang, Haibo Wang, Feng Zhu and Donghang Yan
The Journal of Physical Chemistry B 2008 Volume 112(Issue 22) pp:6786-6792
Publication Date(Web):May 8, 2008
DOI:10.1021/jp7118795
We systematically investigated the weak epitaxy growth (WEG) behavior of a series of planar phthalocyanine compounds (MPc), i.e., metal-free phthalocyanine (H2Pc), nickel phthalocyanine (NiPc), copper phthalocyanine (CuPc), zinc phthalocyanine (ZnPc), iron phthalocyanine (FePc), cobalt phthalocyanine (CoPc), grown on a p-sexiphenyl (p-6P) monolayer film by selected area electron diffraction (SAED) and atomic force microscopy (AFM). Two types of epitaxial relations, named as incommensurate epitaxy and commensurate epitaxy, were identified between phthalocyanine compounds and the substrate of the p-6P film. The tiny variation of the lattice constant of phthalocyanine compounds can result in different crystal orientations. The change rule of incommensurate and commensurate epitaxy was extracted. The tendency of commensurate epitaxy becomes weaker as the lattice constant b increases, while it gets stronger as the substrate temperature is elevated. Large size and continuous H2Pc films can be obtained by controlling the growth conditions. The WEG method is generally applicable in the whole family of planar phthalocyanine compounds and may be used to fabricate other high-quality organic films.
Co-reporter:Junliang Yang, Tong Wang, Haibo Wang, Feng Zhu, Gao Li and Donghang Yan
The Journal of Physical Chemistry B 2008 Volume 112(Issue 26) pp:7821-7825
Publication Date(Web):June 5, 2008
DOI:10.1021/jp711457p
The large-size domain and continuous para-sexiphenyl (p-6P) ultrathin film was fabricated successfully on silicon dioxide (SiO2) substrate and investigated by atomic force microscopy and selected area electron diffraction. At the optimal substrate temperature of 180 °C, the first-layer film exhibits the mode of layer growth, and the domain size approaches 100 µm2. Its saturated island density (0.018µm−2) is much smaller than that of the second-layer film (0.088µm−2), which begins to show the Volmer−Weber growth mode. The characteristic of liquid-like crystal of p-6P monolayer film and the adequate diffusion of p-6P molecules dominate the formation of large-size domain. The coalescence of large-size domains offers the possibility to grow high-quality p-6P monolayer film which provides excellent substrate for weak epitaxy growth of phthalocyanine compounds.
Co-reporter:Junliang Yang, Tong Wang, Haibo Wang, Feng Zhu, Gao Li and Donghang Yan
The Journal of Physical Chemistry B 2008 Volume 112(Issue 26) pp:7816-7820
Publication Date(Web):May 30, 2008
DOI:10.1021/jp711455u
The para-sexiphenyl (p-6P) monolayer film induces weak epitaxy growth (WEG) of disk-like organic semiconductors, and their charge mobilities are increased dramatically to the level of the corresponding single crystals [Wang et al., Adv. Mater. 2007, 19, 2168]. The growth behavior and morphology of p-6P monolayer film play decisive roles on WEG. Here, we investigated the growth behavior of p-6P submonolayer film as a function of the substrate temperature. Its growth exhibited two different mechanisms at high and low substrate temperature. At high substrate temperature (>60 °C), the mechanism of diffusion-limited aggregation controlled the growth of submonolayer thin film with fractal islands, whereas at low substrate temperature (≤60 °C), the submonolayer thin film was composed of the compact islands. Its growth exhibited another growth mechanism in which the stable compact islands were formed by dissociation and reorganization of the metastable disordered film. The substrate temperature of about 180 °C may be optimal to fabricate high-quality p-6P monolayer film with large-size domains and low saturated island density of about 0.018 µm−2.
Co-reporter:Jiguang Dai, Xiaoxia Jiang, Haibo Wang, Donghang Yan
Thin Solid Films 2008 Volume 516(Issue 10) pp:3320-3323
Publication Date(Web):31 March 2008
DOI:10.1016/j.tsf.2007.09.043
Hexadecafluorophthalocyaninatocopper (F16CuPc)/zinc phthalocyanine (ZnPc) heterojunction layer has been used as buffer layer in organic photovoltaic (OPV) cells based on ZnPc and C60. The F16CuPc/ZnPc heterojunction with highly conductive property decreased the contact resistance between the indium-tin-oxide anode and the organic layer. As a result, the short-circuit current density and fill factor were increased, and the power-conversion efficiency was improved by over 60%. Therefore, the method provides an effective path to improve the performance of OPV cells.
Co-reporter:H. Wang;Y. Geng;J. Yang;F. Zhu;D. Yan
Advanced Materials 2007 Volume 19(Issue 16) pp:2168-2171
Publication Date(Web):20 JUL 2007
DOI:10.1002/adma.200602566
Thin films of phthalocyanine compounds show weak epitaxial growth on a monodomain film of a rod-like molecule (see figure). The resulting organic electronic devices exhibit high charge carrier mobilities close to those of the single-crystal devices.
Co-reporter:J. W. Shi;H. B. Wang;D. Song;H. K. Tian;Y. H. Geng;D. H. Yan
Advanced Functional Materials 2007 Volume 17(Issue 3) pp:
Publication Date(Web):1 FEB 2007
DOI:10.1002/adfm.200790011
Simultaneous introduction of short-range repulsive interactions between dissimilar colloidal particles and attractive interactions between like particles provides a general new route to fabricating self-organizing bipolar devices. By identifying combinations of conductive device materials between which short-range repulsive forces exist in the presence of an intervening liquid, electrochemical junctions can be self-formed, as reported by Chiang and co-workers on p. 379.
The relationship between the performance characteristics of organic field-effect transistors (OFETs) with 2,5-bis(4-biphenylyl)bithiophene/copper hexadecafluorophthalocyanine (BP2T/F16CuPc) heterojunctions and the thickness of the BP2T bottom layer is investigated. Three operating modes (n-channel, ambipolar, and p-channel) are obtained by varying the thickness of the organic semiconductor layer. The changes in operating mode are attributable to the morphology of the film and the heterojunction effect, which also leads to an evolution of the field-effect mobility with increasing film thickness. In BP2T/F16CuPc heterojunctions the mobile charge carriers accumulate at both sides of the heterojunction interface, with an accumulation layer thickness of ca. 10 nm. High field-effect mobility values can be achieved in continuous and flat films that exhibit the heterojunction effect.
Co-reporter:J. W. Shi;H. B. Wang;D. Song;H. K. Tian;Y. H. Geng;D. H. Yan
Advanced Functional Materials 2007 Volume 17(Issue 3) pp:
Publication Date(Web):9 JAN 2007
DOI:10.1002/adfm.200600950
The relationship between the performance characteristics of organic field-effect transistors (OFETs) with 2,5-bis(4-biphenylyl)bithiophene/copper hexadecafluorophthalocyanine (BP2T/F16CuPc) heterojunctions and the thickness of the BP2T bottom layer is investigated. Three operating modes (n-channel, ambipolar, and p-channel) are obtained by varying the thickness of the organic semiconductor layer. The changes in operating mode are attributable to the morphology of the film and the heterojunction effect, which also leads to an evolution of the field-effect mobility with increasing film thickness. In BP2T/F16CuPc heterojunctions the mobile charge carriers accumulate at both sides of the heterojunction interface, with an accumulation layer thickness of ca. 10 nm. High field-effect mobility values can be achieved in continuous and flat films that exhibit the heterojunction effect.
Co-reporter:J. Wang;H. Wang;X. Yan;H. Huang;D. Jin;J. Shi;Y. Tang;D. Yan
Advanced Functional Materials 2006 Volume 16(Issue 6) pp:
Publication Date(Web):16 FEB 2006
DOI:10.1002/adfm.200500111
Ambipolar organic field-effect transistors (OFETs) are produced, based on organic heterojunctions fabricated by a two-step vacuum-deposition process. Copper phthalocyanine (CuPc) deposited at a high temperature (250 °C) acts as the first (p-type component) layer, and hexadecafluorophthalocyaninatocopper (F16CuPc) deposited at room temperature (25 °C) acts as the second (n-type component) layer. A heterojunction with an interpenetrating network is obtained as the active layer for the OFETs. These heterojunction devices display significant ambipolar charge transport with symmetric electron and hole mobilities of the order of 10–4 cm2 V–1 s–1 in air. Conductive channels are at the interface between the F16CuPc and CuPc domains in the interpenetrating networks. Electrons are transported in the F16CuPc regions, and holes in the CuPc regions. The molecular arrangement in the heterojunction is well ordered, resulting in a balance of the two carrier densities responsible for the ambipolar electrical characteristics. The thin-film morphology of the organic heterojunction with its interpenetrating network structure can be controlled well by the vacuum-deposition process. The structure of interpenetrating networks is similar to that of the bulk heterojunction used in organic photovoltaic cells, therefore, it may be helpful in understanding the process of charge collection in organic photovoltaic cells.
Co-reporter:Haibo Wang, Jun Wang, Haichao Huang, Xuanjun Yan, Donghang Yan
Organic Electronics 2006 Volume 7(Issue 5) pp:369-374
Publication Date(Web):October 2006
DOI:10.1016/j.orgel.2006.04.004
A diode with a reverse rectifying characteristics was fabricated based on the organic heterojunction of copper phthalocyanine (CuPc) and copper-hexadecafluoro-phthalocyanine (F16CuPc). At the heterojunction interface, HOMO of CuPc is bended upwards and LUMO of F16CuPc is bended downwards, since the charge carriers were accumulated at both side of the interface, electrons in F16CuPc and holes in CuPc. The thickness of holes accumulated at the CuPc layer is about 10 nm, which was determined by fabricating organic field-effect transistors with active layers in series of thickness. By utilizing the heterojunction-effect, the threshold voltage in organic transistors can be modified.
Co-reporter:J. Zhang;H. Wang;X. Yan;J. Wang;J. Shi;D. Yan
Advanced Materials 2005 Volume 17(Issue 9) pp:
Publication Date(Web):25 APR 2005
DOI:10.1002/adma.200401113
A new class of organic semiconductors based on composites of copper phthalocyanine and nickel phthalocyanine for use in organic thin-film transistors show relatively high mobilities. X-ray diffraction of the composite films, which consist of homogenously sized crystals (see Figure), indicates the presence of a new crystalline phase incorporating both copper and nickel phthalocyanine molecules.
Co-reporter:Xiaolan Qiao, Hao Chang, Lizhen Huang, Jidong Zhang, Hongkun Tian, Yanhou Geng and Donghang Yan
Physical Chemistry Chemical Physics 2012 - vol. 14(Issue 29) pp:NaN10284-10284
Publication Date(Web):2012/06/06
DOI:10.1039/C2CP41248A
The growth process and phase state of 5,5′′-bis(3′-fluoro-biphenyl-4-yl)-2,2′:5′,2′′- terthiophene (m-F2BP3T) thin films were investigated by atomic force microscopy (AFM), in-plane and out-of-plane X-ray diffraction (XRD), and selected area electron diffraction (SAED). Two meso-phases (thin film phases) of m-F2BP3T films on SiO2 surface were obtained in the early stages. The m-F2BP3T films initially exhibited two-dimensional (2D) layers (≤4 ML) followed by three-dimensional (3D) island growth. The film structure evolved two thin film phases in the first four layers and the bulk phase was formed from the fifth layer, which occurred concomitantly with the change of the growth mode. Moreover, the variation of weak epitaxy growth behavior of ZnPc from 2D to 3D growth further reflects that the phase state of the first three layers is different from that of the fourth layer, in spite of ZnPc crystals showing just one orientation corresponding to commensurate epitaxy. The novel phase behavior is closely related to the synergistic effects of the outstanding soft matter properties, limited elasticity of organic molecules, and strain originating from the SiO2 substrate. This study investigates novel phase behavior in organic thin films and provides significant insight into the mechanism of the phase transition.
Co-reporter:Junliang Yang and Donghang Yan
Chemical Society Reviews 2009 - vol. 38(Issue 9) pp:NaN2645-2645
Publication Date(Web):2009/05/27
DOI:10.1039/B815723P
The fabrication of organic semiconductor thin films is extremely important in organic electronic devices. This tutorial review—which should particularly appeal to chemists and physicists interested in organic thin-film growth, organic electronic devices and organic semiconductor materials—summarizes the method of weak epitaxy growth (WEG) and its application in the fabrication of high quality organic semiconductor thin films. WEG achieves the thin-film fabrication of disk-like organic semiconductor molecules with highly structural order, molecular level smoothness and large size domains on amorphous substrate. The organic field-effect transistor devices based on these thin films exhibit a high charge mobility that is comparable with their corresponding single-crystal devices. Moreover, it provides a way to produce organic superlattices.
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![Dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene](/data/chemimg/136100/935280-42-5.png)
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![Stannane, [2,2'-bithiophene]-5,5'-diylbis[tributyl-](/data/chemimg/105800/171290-94-1.png)
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![Thieno[3,2-b]thiophene, 3-bromo-](/data/chemimg/10800/25121-83-9_b.png)
