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Now showing items 1 - 11 of 11

  • Mobility Evaluation of BTBT Derivatives: Limitation and Impact on Charge Transport

    Wawrzinek, Robert   Sobus, Jan   Chaudhry, Mujeeb Ullah   Ahmad, Viqar   Grosjean, Arnaud   Clegg, Jack K.   Namdas, Ebinazar B.   Lo, Shih-Chun  

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  • High Performance p- and n-Type Light-Emitting Field-Effect Transistors Employing Thermally Activated Delayed Fluorescence

    Sobus, Jan   Bencheikh, Fatima   Mamada, Masashi   Wawrzinek, Robert   Ribierre, Jean-Charles   Adachi, Chihaya   Lo, Shih-Chun   Namdas, Ebinazar B.  

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  • Interface Engineering of Solution-Processed Hybrid Organohalide Perovskite Solar Cells

    Zhang, Shanshan   Stolterfoht, Martin   Armin, Ardalan   Lin, Qianqian   Zu, Fengshuo   Sobus, Jan   Jin, Hui   Koch, Norbert   Meredith, Paul   Burn, Paul L.   Neher, Dieter  

    Engineering the interface between the perovskite absorber and the charge-transporting layers has become an important method for improving the charge extraction and open-circuit voltage (V-OC) of hybrid perovskite solar cells. Conjugated polymers are particularly suited to form the hole-transporting layer, but their hydrophobicity renders it difficult to solution-process the perovskite absorber on top. Herein, oxygen plasma treatment is introduced as a simple means to change the surface energy and work function of hydrophobic polymer interlayers for use as p-contacts in perovskite solar cells. We find that upon oxygen plasma treatment, the hydrophobic surfaces of different prototypical p-type polymers became sufficiently hydrophilic to enable subsequent perovskite junction processing. In addition, the oxygen plasma treatment also increased the ionization potential of the polymer such that it became closer to the valance band energy of the perovskite. It was also found that the oxygen plasma treatment could increase the electrical conductivity of the p-type polymers, facilitating more efficient charge extraction. On the basis of this concept, inverted MAPbI(3) perovskite devices with different oxygen plasma-treated polymers such as P3HT, P3OT, polyTPD, or PTAA were fabricated with power conversion efficiencies of up to 19%.
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  • Effect of Solvent Variations in the Alcothermal Synthesis of Template-Free Mesoporous Titania for Dye-Sensitized Solar Cells Applications

    Wawrzynczak, Agata   Polrolniczak, Paulina   Sobus, Jan   Schroeder, Grzegorz   Jurga, Stefan   Selli, Elena  

    A series of 14 mesoporous titania materials has been synthesized using the simple alcothermal template-free method and various alcohols, such as methanol, propanols and butanols, as solvents. All materials were characterized by both wide and small angle XRD, which exhibited the anatase phase with short-range ordered mesoporous structure that is still forming during post synthetic temperature treatment in most of the investigated materials. Nitrogen adsorption-desorption isotherms confirmed the mesoporous structure with surface area ranging from 241 to 383 m(2)g(-1) and pore volumes from 0.162 to 0.473 m(3)g(-1), UV-Vis diffuse reflectance showed the redshift of the absorption edge and the bandgap decrease after post synthetic calcination of the materials presented. The TEM, FT-IR, DTA and TG measurements have been made to well characterize the materials synthesized. The mesoporous samples obtained were applied as anode materials for dye-sensitized solar cells and showed good activity in photon-to-current conversion process with efficiency values ranging from 0.54% to 4.6% and fill factors in the 52% to 67% range. The photovoltaic performances were not as high as those obtained for the materials synthesized by us earlier employing ethanol as a solvent. The differences in the electron lifetime, calculated from electrochemical impedance spectroscopy results and varying between 4.3 to 17.5 ms, were found as a main factor determining the efficiency of the investigated photovoltaic cells.
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  • Optimization of absorption bands of dye-sensitized and perovskite tandem solar cells based on loss-in-potential values.

    Sobus, Jan   Ziolek, Marcin  

    A numerical study of optimal bandgaps of light absorbers in tandem solar cell configurations is presented with the main focus on dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs). The limits in efficiency and the expected improvements of tandem structures are investigated as a function of total loss-in-potential (V(L)), incident photon to current efficiency (IPCE) and fill factor (FF) of individual components. It is shown that the optimal absorption onsets are significantly smaller than those derived for multi-junction devices. For example, for double-cell devices the onsets are at around 660 nm and 930 nm for DSSCs with iodide based electrolytes and at around 720 nm and 1100 nm for both DSSCs with cobalt based electrolytes and PSCs. Such configurations can increase the total sunlight conversion efficiency by about 35% in comparison to single-cell devices of the same VL, IPCE and FF. The relevance of such studies for tandem n-p DSSCs and for a proposed new configuration for PSCs is discussed. In particular, it is shown that maximum total losses of 1.7 V for DSSCs and 1.4 V for tandem PSCs are necessary to give any efficiency improvement with respect to the single bandgap device. This means, for example, a tandem n-p DSSC with TiO2 and NiO porous electrodes will hardly work better than the champion single DSSC. A source code of the program used for calculations is also provided.=20
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  • Factors Affecting the Performance of Champion Silyl-Anchor Carbazole Dye Revealed in the Femtosecond to Second Studies of Complete ADEKA-1 Sensitized Solar Cells

    Sobus, Jan   Gierczyk, Blazej   Burdzinski, Gotard   Jancelewicz, Mariusz   Polanski, Enrico   Hagfeldt, Anders   Ziolek, Marcin  

    Record laboratory efficiencies of dye-sensitized solar cells have been recently reported using an alkoxysilyl-anchor dye, ADEKA-1 (over 14%). In this work we use time-resolved techniques to study the impact of key preparation factors (dye synthesis route, addition of co-adsorbent, use of cobalt-based electrolytes of different redox potential, creation of insulating Al2O3 layers and molecule capping passivation of the electrode) on the partial charge separation efficiencies in ADEKA-1 solar cells. We have observed that unwanted fast recombination of electrons from titania to the dye, probably associated with the orientation of the dyes on the titania surface, plays a crucial role in the performance of the cells. This recombination, taking place on the sub-ns and ns time scales, is suppressed in the optimized dye synthesis methods and upon addition of the co-adsorbent. Capping treatment significantly reduces the charge recombination between titania and electrolyte, improving the electron lifetime from tens of ms to hundreds of ms, or even to single seconds. Similar increase in electron lifetime is observed for homogenous Al2O3 over-layers on titania nanoparticles, however, in this case the total solar cells photocurrent is decreased due to smaller electron injection yield from the dye. Our studies should be important for a broader use of very promising silyl-anchor dyes and the further optimization and development of dye-sensitized solar cells.
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  • Comparison of TiO=E2=82=82 and ZnO solar cells sensitized with an indoline dye: time-resolved laser spectroscopy studies of partial charge separation processes.

    Sobus, Jan   Burdzinski, Gotard   Karolczak, Jerzy   Idigoras, Jesus   Anta, Juan A   Ziolek, Marcin  

    Time-resolved laser spectroscopy techniques in the time range from femtoseconds to seconds were applied to investigate the charge separation processes in complete dye-sensitized solar cells (DSC) made with iodide/iodine liquid electrolyte and indoline dye D149 interacting with TiO2 or ZnO nanoparticles. The aim of the studies was to explain the differences in the photocurrents of the cells (3-4 times higher for TiO2 than for ZnO ones). Electrochemical impedance spectroscopy and nanosecond flash photolysis studies revealed that the better performance of TiO2 samples is not due to the charge collection and dye regeneration processes. Femtosecond transient absorption results indicated that after first 100 ps the number of photoinduced electrons in the semiconductor is 3 times higher for TiO2 than for ZnO solar cells. Picosecond emission studies showed that the lifetime of the D149 excited state is about 3 times longer for ZnO than for TiO2 samples. Therefore, the results indicate that lower performance of ZnO solar cells is likely due to slower electron injection. The studies show how to correlate the laser spectroscopy methodology with global parameters of the solar cells and should help in better understanding of the behavior of alternative materials for porous electrodes for DSC and related devices. =20
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  • Carbazole Dye-Sensitized Solar Cells Studied from Femtoseconds to Seconds-Effect of Additives in Cobalt- and Iodide-Based Electrolytes.

    Sobus, Jan   Kubicki, Jacek   Burdzinski, Gotard   Ziolek, Marcin  

    Comprehensive studies of all charge-separation processes in efficient carbazole dye-sensitized solar cells are correlated with their photovoltaic parameters. An important role of partial, fast electron recombination from the semiconductor nanoparticles to the oxidized dye is revealed; this takes place on the picosecond and sub-nanosecond timescales. The charge-transfer dynamics in cobalt tris(bipyridyl) based electrolytes and iodide-based electrolyte is observed to depend on potential-determining additives in a similar way. Upon addition of 0.5M 4-tert-butylpiridine to both types of electrolytes, the stability of the cells is greatly improved; the cell photovoltage increases by 150-200=E2=80=85mV, the electron injection rate decreases about five times (from 5 to 1=E2=80=85ps(-1) ), and fast recombination slows down about two to three times. Dye regeneration proceeds at a rate of about 1=E2=80=85mus(-1) in all electrolytes. Electron recombination from titania to cobalt electrolytes is much faster than that to iodide ones. =C2=A9 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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  • High Performance p- and n-Type Light-Emitting Field-Effect Transistors Employing Thermally Activated Delayed Fluorescence

    Sobus, Jan   Bencheikh, Fatima   Mamada, Masashi   Wawrzinek, Robert   Ribierre, Jean-Charles   Adachi, Chihaya   Lo, Shih-Chun   Namdas, Ebinazar B.  

    Light-emitting field-effect transistors (LEFETs) are an emerging type of devices that combine light-emitting properties with logical switching function. One of the factors limiting their efficiency stems from the spin statistics of electrically generated excitons. Only 25% of them, short lived singlet states, are capable of light emission, with the other 75% being long lived triplet states that are wasted as heat due to spin-forbidden processes. Traditionally, the way to overcome this limitation is to use phosphorescent materials as additional emission channel harnessing the triplet excitons. Here, an alternative strategy for triplet usage in LEFETs in the form of thermally activated delayed fluorescence (TADF) is presented. Devices employing a TADF capable material, 4CzIPN (2,4,5,6-tetra[9H-carbazol-9-yl]isophthalonitrile), in both n-type and p-type configurations are shown. They manifest excellent electrical characteristics, consistent brightness in the range of 100-1,000 cd m(-2) and external quantum efficiency (EQE) of up to 0.1%, which is comparable to the equivalent organic light-emitting diode (OLED) based on the same materials. Simulation identifies the poor light out-coupling as the main reason for lower than expected EQEs. Transmission measurements show it can be partially alleviated using a more transparent top contact, however more structural optimization is needed to tap the full potential of the device.
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  • Low Amplified Spontaneous Emission Threshold and Efficient Electroluminescence from a Carbazole Derivatized Excited-State Intramolecular Proton Transfer Dye

    Mai, Van T. N.   Shukla, Atul   Mamada, Masashi   Maedera, Satoshi   Shaw, Paul E.   Sobus, Jan   Allison, Ilene   Adachi, Chihaya   Namdas, Ebinazar B.   Lo, Shih-Chun  

    The search for new classes of efficient electroluminescent organic laser dyes with low amplified spontaneous emission (ASE) threshold (Eth) and low optical losses is crucial toward the realization of organic injection lasers. In this work, we report in-depth studies of an organic semiconducting laser dye, benzo[d]thiazol-2-yl)-5-(9H-carbazol-9-yl)phenol (HBT-Cz), and compare the photophysical study with its parent HBT dye. While HBT is not laser-active in solution, the carbazole derivatized dye (i.e., HBT-Cz) showed a low solution ASE threshold of 21 mJ/cm(2), which is comparable to a common high-performing commercial laser dye, Rhodamine 6G (Rh-6G). HBT-Cz also exhibited a low film ASE threshold of 2.4 mu J/cm(2) with a low optical loss coefficient of 1.5 cm(-1), which is the lowest waveguide loss coefficient reported for solution-processed organic semiconductors. Organic light-emitting diodes based on this material showed a high maximum EQE of 1.9%, which is close to the theoretical EQE limit of the emitter, and high brightness of >2,300 cd/m(2). Further insights into the lasing properties of the material were provided by steady state UV-visible spectroscopy, and transient absorption spectroscopy, shedding light on excited-state species absorption. To the best of our knowledge, this is the first report of a solution-processable organic small molecular dye, exhibiting a low ASE threshold and lowest optical loss coefficient, coupled with efficient electroluminescence.
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  • High-Speed OLEDs and Area-Emitting Light-Emitting Transistors from a Tetracyclic Lactim Semiconducting Polymer

    Ahmad, Viqar   Shukla, Atul   Sobus, Jan   Sharma, Anirudh   Gedefaw, Desta   Andersson, Gunther G.   Andersson, Mats R.   Lo, Shih-Chun   Namdas, Ebinazar B.  

    Development of a new class of luminescent materials that show high-speed response, high charge carrier mobility, and high brightness is desirable toward realization of next generation of devices, such as electrically pumped organic lasers, visible light communication instruments, and organic light-emitting transistors. In this paper, high-speed organic light-emitting diodes (OLEDs) and high-performance hybrid light-emitting transistors from a new type of solution processable luminescent material, poly[thiophene-2,5-diyl-alt-5,10-bis((2-hexyldecyl)oxy)dithieno[3,2-c:3 ',2 '-h][1,5]naphthyridine-2,7-diyl] (PTNT), are reported. The OLEDs based on PTNT polymer exhibit a peak brightness of 8 x 10(5) cd m(-2) and 40 MHz modulation frequency under 10 ns pulse operation. This modulation frequency is significantly higher than that of commercially available LEDs, used for visible light communication. Additionally, solution-processed area-emitting hybrid light-emitting transistors with an external quantum yield of 0.25% at brightness of 250 cd m(-2) are demonstrated. Finally, the paper provides device physics and optoelectronic properties of PTNT polymer using ultraviolet photon spectroscopy, inversed photoelectron spectroscopy, and photophysical measurements.
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