Research Highlight Archive
Electron and hole mobility in solution-processed small molecule-fullerene blend: Dependence on the fullerene content
Aung Ko Ko Kyaw, Dong Hwan Wang, Hsin-Rong Tseng, Jie Zhang, Guillermo C. Bazan, and Alan J. Heeger
The authors present a study of electron and hole mobility in blends of the solution-processed small molecule (DTS(PTTh2)2):fullerene as a function of the fullerene content. The mobilities are measured using the Field–Effect Transistor device configuration with the blend as the material in the channel.
Spectral response tuning using an optical spacer in broad-band organic solar cells
Yuliang Zhang, Ajay K. Pandey, Chen Tao, Yuan Fang, Hui Jin, Paul L. Burn, and Paul Meredith
The effect of a zinc oxide optical spacer layer in broad-band polymer-fullerene solar cells is presented. The complimentary absorption in the donor and acceptor components allows photocurrent generation through photoinduced electron and hole-transfer mechanisms.
Localizing trapped charge carriers in NO2 sensors based on organic field-effect transistors
Anne-Marije Andringa, W. S. Christian Roelofs, Michael Sommer, Mukundan Thelakkat, Martijn Kemerink, and Dago M. de Leeuw
This work explores the properties (location) of trapped electrons in field-effect transistors, as alternative detectors of NO2 polutants. All three experiments using different organic semiconductors resulted to charges being trapped at the gate dielectric.
Degradation induced decrease of the radiative quantum efficiency in organic light-emitting diodes
Tobias D. Schmidt, Daniel S. Setz, Michael Flämmich, Bert J. Scholz, Arndt Jaeger, Carola Diez, Dirk Michaelis, Norbert Danz, and Wolfgang Brütting
This paper presents a method that allows one to analyze effects of degradation on the different factors in state-of-the-art organic light-emitting diodes.
High output current in vertical polymer space-charge-limited transistor induced by self-assembled monolayer
Hsiao-Wen Zan, Yuan-Hsuan Hsu, Hsin-Fei Meng, Chian-Hao Huang, Yu-Tai Tao, and Wu-Wei
Using self-assembled monolayer treatment, the authors describe modifications of vertical nano-channel sidewalls in vertical transistors, greatly enhancing the vertical transistor output current to 50-110mA/cm2 at 2V, with an on/off current ration larger than 10,000
Coupled plasmonic modes in organic planar microcavities
Mauro Furno, Malte C. Gather, Björn Lüssem, and Karl Leo
A report on the nature of the resonant modes in organic planar microcavities featuring semi-transparent metallic layers. Symmetric microcavities support a total of four modes originating from the coupling of surface plasmon polaritons, whilst red top-emitting organic light-emitting diodes with one semi-transparent metallic electrode exhibit three coupled plasmonic modes.
Phase separation of co-evaporated ZnPc:C60 blend film for highly efficient organic photovoltaics
Ying Zhou, Tetsuya Taima, Tetsuhiko Miyadera, Toshihiro Yamanari, Michinori Kitamura, Kazuhiro Nakatsu, and Yuji Yoshida
Researchers have coaxed 20-nm-thick ZnPc films on indium tin oxide to adopt a “lying-down” crystalline geometry with grain sizes of about 50 nm. This surface distributed with strong interaction areas and weak interaction areas enables the selective growth of ZnPc and C60 molecules, which not only results in a phase separation but also improve the crystalline growth of C60. This blend film greatly enhances the efficiencies in photocurrent generation and carrier transport, resulting in a high power conversion efficiency.
Irradiation-induced molecular dipole reorientation in inverted polymer solar cell using small molecular electron collection layer
Zai-Quan Xu, Fu-Zhou Sun, Jian Li, Shuit-Tong Lee, Yan-Qing Li, and Jian-Xin Tang
Inverted polymer solar cell is developed using small molecular tris(8-hydroxyquinolinato) aluminum (Alq3) as an electron collection layer between the active layer and indium-tin-oxide bottom cathode.
Near-infrared absorbing semitransparent organic solar cells
Jan Meiss, Felix Holzmueller, Roland Gresser, Karl Leo, and Moritz Riede
The devices employ an indium tin oxide-free top contact, consisting of thin metal films and an additional organic capping layer for enhanced light in/outcoupling. The solar cell encorporates a bulk heterojunction with the donor material Ph2-benz-bodipy, an infrared absorber.
Transparent, near-infrared organic photovoltaic solar cells for window and energy-scavenging applications
Richard R. Lunt and Vladimir Bulovic
Near-infrared absorbing organic photovoltaics are fabricated that are highly transparent to visible light. By optimizing near-infrared optical-interference, power efficiencies of 1.3±0.1% are demonstrated with simultaneous average visible transmission of >65%. A series-integrated array of these transparent cells is capable of powering electronic devices under near-ambient lighting. This architecture suggests strategies for high-efficiency power-generating windows and highlights an application uniquely benefiting from excitonic electronics. Featured in the New York Times.
Magnetic field effects on the electroluminescence of organic light emitting devices: A tool to indicate the carrier mobility
B. F. Ding, Y. Yao, Z. Y. Sun, C. Q. Wu, X. D. Gao, Z. J. Wang, X. M. Ding, W. C. H. Choy, and X. Y. Hou
The magnetoelectroluminescence (MEL) of organic light emitting devices with a N,N -bis(l-naphthyl)-N,N -diphenyl-1,l -biphentl-4,4 -diamine:tris-(8-hydroxyquinoline) aluminum mixed emission layer has been investigated. Our experimental and theoretical results confirm that magnetoelectroluminescence can function as a tool to indicate the mobility.
Electrical characterization of organic resistive memory with interfacial oxide layers formed by O2 plasma treatment
Byungjin Cho, Sunghoon Song, Yongsung Ji, and Takhee Lee
Different interfacial oxide thicknesses sequentially changed the ON and OFF states of the final memory devices. This indicates that the oxidation process should be carefully optimized to provide practical high-performance organic memory.
Dependence of Meyer–Neldel energy on energetic disorder in organic field effect transistors
The Meyer–Neldel rule for charge carrier mobility was studied in C60-based organic field effect transistors (OFETs) fabricated at different growth conditions which changed the degree of disorder in the films. The energetic disorder in the films was found to correlate with a shift in the Meyer–Neldel energy, which is in excellent agreement with the predictions of a hopping-transport model for the temperature dependent OFET mobility in organic semiconductors with a Gaussian density-of-states.
Monolayer dual gate transistors with a single charge transport layer
We investigate the electrical transport in a dual gate self-assembled monolayer field-effect transistor and present a detailed analysis of the importance of the contact geometry in monolayer field-effect transistors.
Multilayered graphene used as anode of organic light emitting devices
Our device structure is Al/glass/multilayered graphene/V2O5/NPB/CBP:(ppy)2Ir(acac)/Bphen/Bphen:Cs2CO3/Sm/Au. The maximum luminance efficiency and maximum power efficiency reach 0.75 cd/A and 0.38 lm/W, respectively.
Energy level evolution of molybdenum trioxide interlayer between indium tin oxide and organic semiconductor
The thickness dependance of molybdenum trioxide interlayer between conducting indium tin oxide and chloro-aluminum pthalocyanine has been investigated with ultraviolet photoemission spectroscopy and inverse photoemission spectroscopy. A possible explanation is deduced for the observed reduction in series resistance by the insertion of the insulating layer.
Chemically modified ink-jet printed silver electrodes for organic field-effect transistors
Solution-based deposition of F4TCNQ onto ink-jet printed silver electrodes formed using either a nanoparticle-based or a metal organic decomposition ink, lead to a greater than tenfold improvement in FET mobility.
Temperature-dependent transition from injection-limited to space-charge-limited current in metal-organic diodes
Yi Zheng, Andrew T. S. Wee, Cedric Troadec, and N. Chandrasekhar
Here we show experimentally that charge transport in MO diodes is a complex interplay between injection-limited current (ILC) and space-charge-limited current (SCLC). We report the experimental observation of ILC-to-SCLC transition in Ag/pentacene/Ag diodes as a function of temperature.
Tilted bulk heterojunction organic photovoltaic cells grown by oblique angle deposition
Ning Li and Stephen R. Forrest
Obliquely deposited donor chloroaluminum phthalocyanine (ClAlPc) films on indium tin oxide have surface feature sizes of ~30 nm, resulting in ClAlPc/C60 donor-acceptor heterojunctions (HJs) with approximately twice the interface area of HJs grown at normal incidence. This results in nearly twice the external quantum efficiency in the ClAlPc absorption band compared with analogous, planar HJs.
Three-dimensional fabrication of optically active microstructures containing an electroluminescent polymer
C. R. Mendonca, D. S. Correa, F. Marlow, T. Voss, P. Tayalia, and E. Mazur
In this paper, we use two-photon absorption polymerization to fabricate optically active microstructures containing the conductive and luminescent polymer poly(2-methoxy-5-(2 -ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV). The microstructures retain the emission characteristics of MEH-PPV and allow waveguiding of locally excited fluorescence when fabricated on top of low refractive index substrates.
Organic light-emitting diode with liquid emitting layer
Denghui Xu and Chihaya Adachi
We demonstrate an original organic light-emitting diode (OLED) having a neat liquid host of 9-(2-ethylhexyl)carbazole (EHCz) doped with a guest emitter of 5,6,11,12-tetraphenylnapthacene (rubrene). We demonstrate that the liquid organic semiconducting layer transports charge carriers, leading to electroluminescence from rubrene.
In situ intercalation strategies for device-quality hybrid inorganic-organic self-assembled quantum wells
K. Pradeesh, J. J. Baumberg, and G. Vijaya Prakash
Thin films of self-organized quantum wells of inorganic-organic hybrid perovskites are formed from a simple intercalation strategy to yield well-ordered uniform films over centimeter-size scales that compare favorably with traditional solution-chemistry-synthesized thin films. We demonstrate the potential of this method for electronic and photonic device applications.
Enhanced open-circuit voltage in polymer solar cells
Jie Luo, Hongbin Wu, Chao He, Aiyuan Li, Wei Yang and Yong Cao
The open-circuit voltage of polymer solar cells can be enhanced by 0.3 V by inserting a thin layer of alcohol/water-soluble polyelectrolyte between the active layer and metal electrode. The origin of the increase can be attributed to the superposition of the built-in field with the interfacial dipole of the interlayer, and the existence of the interlayer as a dielectric was confirmed by ac impedance spectroscopy.
Improved bulk heterojunction organic solar cells employing C70 fullerenes
Steffen Pfuetzner, Jan Meiss, Annette Petrich, Moritz Riede, and Karl Leo
We show that the fullerene C70 is suitable to replace C60 as electron transporter and acceptor in small-molecule organic solar cells. The higher absorption of C70 leads to external quantum efficiencies of over 50% in the spectral range 500–700 nm due to a higher photocurrent, while fill factor and open-circuit voltage in solar cells containing C70 remain comparable to those with C60.