Dashan Qin

Hebei University of Technology, Ho-pei-ts’un, Beijing, China

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Publications (15)29.9 Total impact

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    ABSTRACT: In this study, inverted organic light emitting diodes (OLEDs) have been fabricated using the doped p-n heterojunction composed of poly(3,4-ethylenedioxythiophene) :poly(styrenesulfonate) (PEDOT:PSS) and lithium carbonate doped bathocuproine (Li2CO3:BCP) to provide the electron current. The field-induced charge-carrier separation at the doped organic/organic heterointerface was adopted to illuminate the process of generating electron current. Nevertheless, the performance of the inverted OLEDs remained nearly invariable when the PEDOT:PSS thickness ranged from 15 to 38 nm. This was understood mostly based on the temporary reduction of the PEDOT+ to the PEDOT0 due to the localized electron in the PSS- being repelled back to the highest occupied molecular orbital of the PEDOT+ by electrons accumulated at the cathode/PEDOT:PSS interface. The current research presents an insightful understanding of the electrical properties of an organic doped p-n junction that is reversely biased.
    Physica Scripta 12/2013; 89(1). · 1.03 Impact Factor
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    ABSTRACT: The hole-injecting structure of 15 nm MoO3-doped 4,4-N,N-bis [N-1-naphthyl-N-phenyl-amino]biphenyl (NPB:MoO3)/5 nm MoO3-doped 4,4′-N,N′-dicarbazole-biphenyl (CBP:MoO3) has been used in organic light emitting diodes (OLEDs). It was found that a device using the 15 nm NPB:MoO3/5 nm CBP:MoO3/NPB combination was superior to one adopting the 20 nm NPB:MoO3/NPB combination due to two major causes: the NPB:MoO3/CBP:MoO3 interface is a quasi-ohmic contact, and the hole transport barrier from CBP:MoO3 to NPB is smaller than that from NPB:MoO3 to NPB; moreover, it outperformed the device employing the 20 nm CBP:MoO3/NPB combination, mostly because of the higher conductivity of NPB:MoO3 compared to CBP:MoO3. We demonstrate that using a structure resulting from uniting two p-doped hole transporters is a beneficial, simple method of achieving an improved trade-off between high conductivity and small hole transport barrier, thereby leading to a significantly reduced ohmic loss in the hole current conduction in the OLEDs, relative to the single p-doped layers.
    Applied Physics A 11/2013; · 1.69 Impact Factor
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    ABSTRACT: The combination of MoO3-doped 4,4-N,N-bis [N-1-naphthyl-N-phenyl-amino]biphenyl (NPB:MoO3) and 4,4′-N,N′-dicarbazole-biphenyl (CBP:MoO3) was used to enhance the hole conduction in organic light-emitting diodes (OLEDs). It is found that the OLED using NPB:MoO3 10 nm/CBP:MoO3 5 nm showed a much increased current density than the one using NPB:MoO3 5 nm/CBP:MoO3 5 nm at a given voltage larger than 4 V, mainly because the hole transport barrier across the p-doped heterojunction in the former device became smaller than that in the latter device with the driving voltage increasing, despite the fact that the 10-nm NPB:MoO3 in the former device caused more Ohmic loss than the 5-nm one in the latter device. As a result of the higher conductivity of NPB:MoO3 than that of CBP:MoO3, the OLED using the combination of 15-nm NPB:MoO3 and 5-nm CBP:MoO3 showed significantly increased performance than the one using the single 20-nm CBP:MoO3. We provide a useful way of advancing the OLEDs toward the practical applications in general lighting and flat-panel displays.
    Physica Status Solidi (A) Applications and Materials 06/2013; 210(6). · 1.53 Impact Factor
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    ABSTRACT: We report the manageable formation of the gradient-layered poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester (P3HT/PCBM) blend film by spin coating via introducing bathocuproine (BCP) into the mixed P3HT/PCBM solution. The BCP can improve the aggregation and thereby the preferential precipitation of PCBM during the spin-coating process, leading to the gradient-layered phase separation of P3HT and PCBM. The regular solar cells using the gradient-layered ternary blend films gave poor photovoltaic performance, due to the mismatch between the polarity of the regular-device structure and the vertical composition profile of the ternary blend film. By contrast, in the inverted solar cell, the gradient-layered ternary blend film could provide the increased device performance over the conventional bulk heterojunction binary blend films.
    physica status solidi (a) 06/2012; 209(6):1150-1156. · 1.21 Impact Factor
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    ABSTRACT: Inverted bottom-emission organic light emitting diodes (IBOLEDs) employing the electron injection structure of indium tin oxide (ITO)/1,4,5,8-naphthalene-tetracarboxylic-dianhydride (NTCDA)/Li2CO3 doped bathocuproine (BCP) (1:4 Li2CO3:BCP) were fabricated, where NTCDA and BCP stand for NTCDA and BCP, respectively. The NTCDA on ITO was characterized crystalline and n-doped as a result of the interaction between ITO and NTCDA. Compared to the IBOLED using the electron injection structure of ITO/10 nm 1:4 Li2CO3:BCP, the one utilizing the electron injection structure of ITO/3 nm NTCDA/7 nm 1:4 Li2CO3:BCP showed the remarkable increases in both current density and efficiency, mainly due to the higher electron conductivity of n-doped NTCDA than that of n-doped BCP. The dependence of the current conduction in IBOLED on the thickness of NTCDA was investigated. We provide a simple method to significantly enhance the performance of IBOLEDs.
    physica status solidi (a) 04/2012; 209(4):790-794. · 1.21 Impact Factor
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    ABSTRACT: Two organic light-emitting diodes (OLEDs) using the hole current structures of 2:1 NPB:MoO3 5 nm/2:1 CBP:MoO3 5 nm/CBP and 2:1 NPB:MoO3 10 nm/CBP have been fabricated, where NPB and CBP stand for N,N′-bis-(1-naphthl)-diphenyl-1,1′-biphenyl-4,4′-diamine and 4,4′-N,N′-dicarbazole-biphenyl, respectively. Despite that 2:1 CBP:MoO3 is proven to be more resistive than 2:1 NPB:MoO3 via comparing the I–V characteristics of the hole-only devices, the former OLED using two p-doped layers shows significantly improved I–V characteristics over the latter one using a single p-doped layer, mostly because the whole barrier height for hole transport across the 2:1 NPB:MoO3/2:1 CBP:MoO3 and 2:1 CBP:MoO3/CBP interfaces in the former device is 0.22 eV smaller than that for hole transport across the 2:1 NPB:MoO3/CBP interface in the latter device. We provide a simple, effective method to enhance the hole current in OLEDs.
    Semiconductor Science and Technology 01/2012; 27(4). · 1.92 Impact Factor
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    ABSTRACT: Planar copper phthalocyanine (CuPc)/C 60 heterojunction solar cells with a 2 nm layer of bathocuproine (BCP) inserted into the C 60 layer were fabricated and characterized. The 2 nm BCP layer in the devices was used as an electronically selective sieve allowing the electron current through but blocking the excitons in the C 60 layer. By combining the experimental results with the optical modeling, the effective triplet exciton diffusion length in C 60 was confirmed to be 30–35 nm under the device working condition. We demonstrate a simple, useful method to determine the exciton diffusion lengths of organic electron acceptors. 1 Introduction Organic small-molecular donor/ acceptor heterojunction solar cells have drawn considerable attentions during the past two decades [1–5], since the first demonstration of the double-layer structure in 1986. The best power conversion efficiencies (PCEs) obtained from single-cell structures were reported around 4–5% [6, 7]. By using a properly designed asymmetric tandem structure, a PCE of 5.7% was achieved [8]. Nevertheless, in order to exceed the benchmark of 10% required for the commercial applications of organic heterojunction solar cells, more efforts are needed to develop new high-function organic materials and to better understand the device operation mechanisms. In particular, it is crucial to precisely measure the exciton diffusion length (L D) of organic electron acceptors under the operation condition. The L D is widely considered as a very important parameter for organic photovoltaic materials, because it plays an important role in determining the optimal thickness of the light-absorbing layer and, thereby, the solar power-utilizing efficiency of a planar heterojunction solar cell. There are two methods that are regularly used so far to determine the L D for organic materials: one is
    Physica Status Solidi (A) Applications and Materials 08/2011; 208(8):1967. · 1.53 Impact Factor
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    ABSTRACT: Inverted bottom-emission organic light emitting diodes (IBOLEDs) using MoO3 for both hole and electron injections were fabricated. The IBOLED using 10 nm MoO3 for hole injection and 5 nm MoO3/5 nm Li2CO3 doped bathocuproine (Li2CO3:BCP, 1:4 in mass) for electron injection showed nearly same I–V characteristics as the reference device utilizing 10 nm MoO3 for hole injection and 10 nm 1:4 Li2CO3:BCP for electron injection, whereas, the former device provided increased current efficiencies than the latter device, as a result of the relieved diffusion of n-typed dopant into the emissive layer in the former device. We provide an efficient, low-cost alternative to realizing the electron injection in IBOLEDs.
    Physica Status Solidi (A) Applications and Materials 08/2011; 208(8). · 1.53 Impact Factor
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    ABSTRACT: Two-unit tandem organic light emitting diodes (OLEDs) employing two kinds of interconnecting structures, i.e. 5 nm lithium carbonate doped PTCDA (1:2 Li2CO3:PTCDA)/5 nm MoO3 and 5 nm Li2CO3 doped BCP (1:4 Li2CO3:BCP)/5 nm MoO3, have been fabricated, where PTCDA and BCP stand for 3, 4, 9, 10 perylenetetracarboxylic dianhydride and bathocuproine, respectively. Compared to the tandem OLED using the interconnecting structure of 5 nm 1:4 Li2CO3:BCP/5 nm MoO3, the one utilizing 5 nm 1:2 Li2CO3:PTCDA/5 nm MoO3 showed nearly same power efficiency and decreased operating voltage, mainly attributed to the higher electron conductivity of 1:2 Li2CO3:PTCDA relative to 1:4 Li2CO3:BCP. The charge generation and electron injection processes based on the interconnecting structure of 5 nm 1:2 Li2CO3:PTCDA/5 nm MoO3 were also discussed. We provide a simple and effective connecting structure to enhance the current conduction for tandem OLEDs.
    Semiconductor Science and Technology 07/2011; 26(9):095011. · 1.92 Impact Factor
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    ABSTRACT: The influence of pressure on the morphology of blend film consisted of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) has been studied in the solvent evaporating process. It is found that the crystalline aggregation of the P3HT component was markedly enhanced in the blend film grown under reduced pressure, compared to that under normal atmospheric pressure. Moreover, the blend film grown under reduced pressure offered greater short-circuit current and power conversion efficiency of a device than that grown under normal atmospheric pressure, mainly ascribing to it that the optimized morphology of the blend film via decreasing pressure improved transport of photo-charges. The pressure effect of PCBM vertical diffusion in the blend film is also discussed.
    Semiconductor Science and Technology 01/2010; 25(9). · 1.92 Impact Factor
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    ABSTRACT: A task-specific ionic liquid containing a carboxylate group with the ability to dissolve metal oxide and organic ligands has been used as the solvent to prepare lanthanide complexes without the addition of extra solvent; thus a soft material with intense photoluminescence has been obtained by directly dissolving Eu(2)O(3), 2-thenoyltrifluoroacetone (TTA) and 1,10-phenanthroline (Phen) into the task-specific ionic liquid.
    Chemical Communications 12/2008; · 6.38 Impact Factor
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    ABSTRACT: Luminescent lanthanide-complex-bridged polysilsesquioxanes were prepared by sol–gel processing of a monomer with a large heterocyclic bridging group in the presence of lanthanide ions under acidic conditions. SEM, XRD, FTIR, luminescence spectra and luminescence decay analysis were used to characterize the obtained materials. The 5D0 quantum efficiency and the number of the water molecules coordinated to the Eu3+ ion were theoretically estimated on the basis of emission spectra and the lifetime of the 5D0 state.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
    Berichte der deutschen chemischen Gesellschaft 09/2008; 2008(30):4781 - 4785. · 2.94 Impact Factor
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    ABSTRACT: Organic light emitting diodes using a mixed layer of electron acceptor 3, 4, 9, 10 perylenetetracarboxylic dianhydride and electron donor copper phthalocyanine (PTCDA:CuPc) on indium tin oxide (ITO) anodes were fabricated. The device properties were found to be strongly dependent on the thickness of the PTCDA:CuPc film: both the power efficiency and the driving voltage of the device were optimized with a thickness of PTCDA:CuPc ranging from 10 to 20 nm. As compared to the conventional ITO/CuPc hole injection structure, the ITO/PTCDA:CuPc hole injection structure could remarkably enhance both the luminance and the power efficiencies of devices. A mechanism of static-induced, very efficient hole-electron pairs generation in mixed PTCDA:CuPc films was proposed to explain the experimental phenomena. The structural and optical properties of PTCDA:CuPc film were examined as well.
    Journal of Applied Physics 01/2007; 101. · 2.21 Impact Factor
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    ABSTRACT: The inverted polymer:fullerene solar cells with structure of ITO/TiO2/P3HT:PCBM/MoO3/Al have been fabricated, where P3HT and PCBM stand for poly (3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester, respectively. It is discovered that the P3HT:PCBM blend film manipulated into the improved stratification structure, characterized as P3HT crystallite-rich zone close to the top surface and PCBM constituent-rich zone adjacent to the bottom surface, can offer nearly the same power conversion efficiency of solar cell, compared to the one grown into the bulk heterojunction structure, characterized as the bicontinuous interpenetrating network of P3HT and PCBM. We provide an alternative insight to the morphology control of inverted polymer:fullerene solar cells.
    Applied Physics A 104(1):47-53. · 1.69 Impact Factor
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    ABSTRACT: The ternary blend films have been fabricated via adding 4,4′-N,N′-dicarbazole-biphenyl (CBP, a hole transport material widely used in organic light emitting diodes) into the poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methyl ester (P3HT: PCBM). Despite the wide bandgap (3.1 eV) of the CBP, the solar cell utilizing the optimized P3HT:PCBM:CBP blend film showed an increase of 16% in power conversion efficiency and 25% in short-circuit current than the compared standard P3HT:PCBM blend film. This is attributed to the fact that the addition of the CBP could enhance the aggregation of the P3HT chains and thereby reduce the hole-electron recombination at the interface of P3HT and PCBM. We provide a simple, effective way to improve the performance of P3HT based bulk heterojunction solar cells.
    Science China: Physics, Mechanics and Astronomy 56(3). · 1.17 Impact Factor