Comment on "Interface state recombination in organic solar cells"

In a recent paper, Street et al. [Phys. Rev. B 81, 205307 (2010)] propose first order recombination due to interface states to be the dominant loss mechanism in organic bulk heterojunction solar cells, based on steady-state current--voltage characteristics. By applying macroscopic simulations, we found that under typical solar cell conditions, monomolecular or bimolecular recombination cannot be inferred from the slope of the light intensity dependent photocurrent. In addition, we discuss the validity of calculating a mobility--lifetime product from steady-state measurements. We conclude that the experimental technique applied by Street et al. is not sufficient to unambiguously determine the loss mechanism.Comment: 4 pages, 2 figures. Corrected Eqns. (2) and (4): 1/... was missin

Electrical and optical properties of carbon nanotube intra-connects and conductive polymers

Growth of individual carbon nanotube (CNT) intra-connects (bridges) between two prefabricated electrodes is a great challenge and a pre-requisite to the development of single electron devices. In this thesis, CNT intra-connects were fabricated and studied. Later on, the intra-connects were deposited with electrically conductive polymer (ECP) in the realization of CNT/ECP hybrids. The process started by realizing two electrodes with sharp end on a silicon wafer using e-beam lithography. The intra-connects were then grown by use of chemical vapor deposition (CVD) technique. The intra-connects were later electroplated by various conductive polymers. The morphology, electrical conductivity of these intra-connects as well as their Raman spectroscopy signatures were studied. Scanning electron microscopy (SEM) was also employed. The CNT intra-connects were well-aligned from tip to tip. Their Raman spectra indicated the existence of CNT channels between metal tips and nowhere else on the wafer. Enhancement of photoconductance has been shown to correlate with a novel negative differential resistance (NDR) effect. Electroplated intraconnects exhibited unique properties both for multi-walled and single-walled carbon nanotube channels

Nucleation and growth mechanism of polycarbazole deposited by electrochemistry

Polycarbazole (PCz) thin films have been deposited by electro-oxidation of carbazole in LiClO4 + anhydrous acetonitrile onto SnO2 coated glass substrates, by potentiostatic method and the nucleation and growth mechanism (NGM) were studied. The obtained current time transients (j-t) were fitted using a mathematical equation with three contributions: instantaneous nucleation with two-dimensional (IN2D) or three-dimensional (IN3D) growth, and also a progressive nucleation with three dimensional (PN3D) growth. At the beginning, the IN2D contribution is predominant but, quickly the IN3D processes become more important. At a deposition time t > 17 s the IN3D corresponds to 80 % of the total current. The visualization by scanning electron microscopy of the surface morphology of the PCz films is in agreement with the NGM proposed by the mathematical method. The film covers very rapidly the SnO2 under layer related to the 2D process, even if some heterogeneities randomly distributed in the films, issued from the 3D processes, are also visible. After two minutes of deposition, the roughness of the whole surface of the films corroborates the 3D processes domination. Therefore, the information directly obtained from the (j-t) transients is a suitable and very useful tool to predict the working conditions in order to control the type of morphology of the film prepared by electropolymerization

Polycarbazole and Its Derivatives: Synthesis and Applications. A Review of the Last 10 Years

Polycarbazole and its derivatives have been extensively used for the last three decades, although the interest in these materials briefly decreased. However, the increasing demand for conductive polymers for several applications such as light emitting diodes (OLEDs), capacitators or memory devices, among others, has renewed the interest in carbazole-based materials. In this review, the synthetic routes used for the development of carbazole-based polymers have been summarized, reviewing the main synthetic methodologies, namely chemical and electrochemical polymerization. In addition, the applications reported in the last decade for carbazole derivatives are analysed. The emergence of flexible and wearable electronic devices as a part of the internet of the things could be an important driving force to renew the interest on carbazole-based materials, being conductive polymers capable to respond adequately to requirement of these devices

Triazine containing N-rich microporous organic polymers for CO2 capture and unprecedented CO2/N2 selectivity

Targeted synthesis of microporous adsorbents for CO2 capture and storage is very challenging in the context of remediation from green house gases. Herein we report two novel N-rich microporous networks SB-TRZ-CRZ and SB-TRZ-TPA by extensive incorporation of triazine containing tripodal moiety in the porous polymer framework. These materials showed excellent CO2 storage capacities: SB-TRZ-CRZ displayed the CO2 uptake capacity of 25.5 wt% upto 1 bar at 273 K and SB-TRZ-TPA gave that of 16 wt% under identical conditions. The substantial dipole quadruple interaction between network (polar triazine) and CO2 boosts the selectivity for CO2/N2. SB-TRZ-CRZ has this CO2/N2 selectivity ratio of 377, whereas for SB-TRZ-TPA it was 97. Compared to other porous polymers, these materials are very cost effective, scalable and very promising material for clean energy application and environmental issues

Open-Circuit Voltage in Inverted Polycarbazole:Fullerene Bulk Heterojunction Solar Cells

The correlation between cathode work function and open-circuit voltages (Voc) in inverted polycarbazole:fullerene (PCDTBT:PC70BM) bulk-heterojunction solar cells has been investigated by postannealing of indium tin oxide (ITO) electrodes. The ITO function is seen to change from 4.2 to 4.5 eV without the need to insert additional interfacial layers with annealing temperature up to 400 °C. The best device performance was obtained at room temperature with the ITO work function of 4.2 eV with a Voc of 0.89 eV, a Jsc of 8.06 mA·cm-2, a fill factor (FF) of 64.70%, and a power conversion efficiency of 4.62%. Together with previously published results, we are able to extract two regimes of Voc dependence on the cathode work function: first, a linear relationship when the cathode work function exceeds the lowest unoccupied molecular orbital (LUMO) of PCBM and, second, a constant Voc regime when the ITO work function reduces below the LUMO level. These results provide general guidelines for the cathode contact design in inverted polymer solar cells

Multi-walled carbon nanotube electrodes for sodium borohydride fuel cell

Borohydride fuel cell has been constructed for the first time using multi-walled carbon nanotubes (MCNT), functionalized MWCNT, platinized MWCNT or polycarbzole (Pcz) as electrodes. The output characteristics of borohydride fuel cell with platinized MWCNT electrodes have been shown to be superior to the conventional graphite based borohydride fuel cells. The catalytic activity of platinized carbon nanotubes has also been established in this study. The MWCNTs have been functionalized by refluxing in 60-70% nitric acid for a period of 12 hours. The functionalized MWCNTs were characterized by FTIR and TGA. Platinization of MWCNTs was carried out electrochemically from chloroplatinic acid. Platinization of the tubes was demonstrated through SEM and XRD. Cyclic Voltammetry was used to characterize the platinum in MWCNT. Fuel cells were constructed using MWCNT of different forms as the anode and commercially available oxygen electrode as the cathode. The current values at different loads were measured and plotted to construct the load curves . From this data, the power density maps were generated. The power output of borohydride fuel cell has been shown to be higher than the graphite based fuel cell. The performance of borohydride fuel cells with Pcz electrode could not be decisive as the polymer deposited on platinum was used in the experiments. The polymer tends to peel off with time due to hydrogen bubbles generated in the medium. In the short time of the cell operation, it produced open circuit voltage of 1.369 V that is about 50% more than the commercially available borohydride fuel cell. However, it was noticed that it functions well as the cathode material in the borohydride fuel cells

FLOATING-GATE TRANSISTOR PHOTODETECTOR WITH LIGHT ABSORBING LAYER

A field effect transistor photodetector that can operate in room temperature includes a source electrode, a drain electrode, a channel to allow an electric current to flow between the drain and source electrodes, and a gate electrode to receive a bias voltage for controlling the current in the channel. The photodetector includes a light-absorbing material that absorbs light and traps electric charges. The light-absorbing material is configured to generate one or more charges upon absorbing light having a wavelength within a specified range and to hold the one or more charges. The one or more charges held in the light-absorbing material reduces the current flowing through the channel

Luminescent and Swellable Conjugated Microporous Polymers for Detecting Nitroaromatic Explosives and Removing Harmful Organic Vapors

Four new conjugated microporous polymers (CMPs) were synthesized by a Buchwald-Hartwig (BH) cross-coupling reaction of tri-and tetrafunctionalized precursors to yield materials with tunable surface area and pore size distribution. This approach yielded LPCMP1-4, CMPs with significantly higher Brunauer-Emmett-Teller (BET) surface areas (more than 5 times higher) than other related BH-based CMPs. These CMPs possess not only high BET specific surface areas and high chemical and thermal stabilities, but also exhibit outstanding swellability. To the best of our knowledge, swellable behavior was studied in great detail for CMPs for the first time, with the greatest degree of swelling for methanol reaching 16.5 and 16.3 mL g -1 for LPCMP1 and LPCMP3, respectively. Owing to their excellent swellability, we further studied the adsorption capacity of these CMPs for different toxic organic vapors (including toluene and methanol). LPCMP1 and LPCMP3 adsorbed 124 and 117 mg g -1 toluene, respectively, at saturated vapor pressure. For methanol, the adsorption capacities of LPCMP1 and LPCMP3 were up to 250 and 215 mg g -1, respectively, which are the highest recorded values when compared with published data for CMPs, HCPs, MOFs, and porous carbons. These materials are promising candidates for the removal and elimination of hazardous organic vapors and chemical warfare agents. Moreover, all the polymers show high sensitivity to nitroaromatic explosives. LPCMP2 and LPCMP4 exhibit high selectivity for TNT and may be suitable as new candidates to selectively detect TNT for security or environmental applications. </p