Carrier conduction mechanism for Phosphorescent materials doped organic semiconductor

The mobility of charge carriers has been investigated in the pristine and phosphorescent material doped 4,4 ,4 -tris N-carbazolyl triphenylamine TCTA using time-of-flight photoconductivity technique. Doping phosphorescent material fac-tris 2-phenylpyridine iridium Ir ppy 3 increases the electron mobility whereas the hole mobility decreases to the order of 10−4–10−6 cm2 /V s measured at room temperature with different bias voltages. The analysis of field and temperature dependences of the mobility agrees well with the Gaussian disorder model. The calculated positional disorders for TCTA, Ir ppy 3-doped TCTA, and tris 1-phenylisoquinoline iridium Ir piq 3 -doped TCTAare 0.12, 2.05, and 1.62 for hole, respectively; 3.89 for electron in only Ir ppy 3-doped TCTA. The ambipolar transport for holes and electrons is possible by doping TCTA with Ir ppy 3 green dopant whereas only hole transport with reduced mobility is achieved for Ir piq 3 red dopant

Investigation into the Thermal Annealing Effect on the Photovoltaic Properties of Organic Solar Cells based on CuPc/C60 Heterojunctions

We studied the effect of post-annealing treatment on the photovoltaic (PV) properties of or- ganic solar cells based on copper phthalocyanine (CuPc)/fullerene (C60) heterojunctions. In the device structure of ITO/CuPc (30 nm)/C60(40 nm)/BCP(10 nm)/LiF(0.5 nm)/Al, where BCP is 2,9-dimethyl-4,7-diphenyl-phenanthroline acting as an exciton blocking layer, a maximum power conversion effciency (np) of about 1 % under an AM 1.5 solar illumination intensity of 100 mW/cm2 was obtained at room temperature. By measuring the PV characteristics for the devices annealed at various temperatures for 30 minutes, we found that the short-circuit current and e ciency increased with increasing annealing temperature up to 100 C (np 1:3 %) and then decreased at higher temperatures. We analyzed the effect of thermal annealing on the improved device performance by measuring the optical absorption spectra and the X-ray diffraction patterns of the CuPc/C60 films

Electrical impedance studies of the effect of a buffer layer on organic bulk-hetrojunction solar cells

The effect of a buffer layer on organic bulk hetrojunction solar cells of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61 butyric acid methyl ester fullerene derivative (PCBM) has been studied using impedance spectroscopy in the frequency range between 100 Hz and 1 MHz. The buffer layer interfaces with a metallic contact and with the organic bulk materials in uence the effciency and the stability of devices. Thermal annealing of the devices improves the interface with the buffer layer, thereby lowering the majority and the minority carrier injection voltage. The photocurrent density-voltage (J-V) characteristics show that the fill factor of the device with a molybdenum-oxide (MoO3) buffer layer is higher than that of the device with a poly (3, 4- ethylenedioxy-thiophene):polystyrenesulfonate (PEDOT:PSS) buffer layer. The equivalent circuit analysis for the PEDOT:PSS and the MoO3 buffer-layer devices shows that the device's capacitance and resistance for MoO3 is lower than that for PEDOT:PSS under illumination. The effciency of the thermally-annealed PEDOT:PSS and MoO3 buffer-layer devices are 2.95 and 3.44 %, respectively. The lower effciency of the PEDOT:PSS buffer-layer devices can be attributed to the formation of a thin insulator layer at the PEDOT:PSS/P3HT:PCBM interface under illumination

Charge transport in amorphous low bandgap conjugated polymer/fullerene films

Copyright (2012) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.The structural and charge transport properties of a low bandgap copolymer poly(3-hexylthiophene-alt-6,7-dimethyl-4,9-bis-(4-hexylthien-2yl)-[1,2,5]thiadiazolo[3,4-g]quinoxaline) (P(3HT-MeTDQ)) and its blend with [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) are investigated. Thermal analysis, X-ray scattering diffraction (XRD), atomic force microscopy and transmission electron microscopy (TEM) of P(3HT-MeTDQ) reveal that the polymer is amorphous in solid state. As the hole mobility of P(3HT-MeTDQ) was measured by the time-of-flight photoconductivity method, the mobility was 3.35 x 10(-4) cm(2)/Vs, which is very comparable to that of semicrystalline poly(3-hexylthiophene). When the mobility of amorphous P(3HT-MeTDQ) was analyzed according to the Gaussian disorder model, the polymer has the energetic and positional disorders with the values of sigma = 62 meV and Sigma = 1.7, respectively, indicating that the polymer has a relatively narrow Gaussian distribution of transport states. Interestingly, when P(3HT-MeTDQ) is blended with PCBM, the amorphous P(3HT-MeTDQ) becomes partially ordered, as evidenced by observation of two discernible XRD peaks at 20 = 5 degrees (d = 17.7 angstrom) and 25.5 degrees (d = 3.5 angstrom) corresponding to the interchain distance and pi-stacking distance, respectively. The bicontinuous network morphology was identified at the blend with 60 wt.% PCBM by TEM, at which the charge carrier transport changes from hole-only to ambipolar. (C) 2012 American Institute of Physics. [doi:10.1063/1.3686633]OAIID:oai:osos.snu.ac.kr:snu2012-01/102/0000001236/2SEQ:2PERF_CD:SNU2012-01EVAL_ITEM_CD:102USER_ID:0000001236ADJUST_YN:YEMP_ID:A004558DEPT_CD:445CITE_RATE:2.168FILENAME:2. Charge Transport in Amorphous.pdfDEPT_NM:재료공학부EMAIL:[email protected]_YN:YCONFIRM:

Anion‐Vacancy‐Defect Passivation of a 2D‐Layered Tin‐Based Perovskite Thin‐Film Transistor with Sulfur Doping

Metal halide perovskites have attracted a considerable amount of research attention with significant progress made in the field of optoelectronics. Despite their outstanding electrical characteristics, structural defects impede their potential performance due to the polycrystalline nature of solution-processed perovskite films. Herein, the effective p-type doping and defect passivation of phenethylammonium tin iodide ((PEA)(2)SnI4) perovskite films using xanthate additives as a sulfur source is reported. Sulfur can be introduced to the iodine vacancies mainly at the grain boundaries of the perovskite film, passivating the electrical defects originating from the iodine vacancy and increasing the hole concentration. The Fermi-level shift toward the valence band maximum of the sulfur-doped perovskite film is confirmed using ultraviolet photoemission spectroscopy, resulting in p-type doping. Finally, the electrical performance improvement for the 0.2% sulfur-doped (PEA)(2)SnI4 thin-film transistor with a mobility of 1.45 cm(2) V-1 s(-1), an on/off ratio of 2.9 x 10(5) is demonstrated, and hysteresis of 10 V is reduced.11Nsciescopu

Graphene-nanowire hybrid structures for high-performance photoconductive devices

Graphene-CdS nanowire (NW) hybrid structures with high-speed photoconductivity were developed. The hybrid structure was comprised of CdS NWs which were selectively grown in specific regions on a single-layer graphene sheet. The photoconductive channels based on graphene-CdS NW hybrid structures exhibited much larger photocurrents than graphene-based channels and much faster recovery speed than CdS NW network-based ones. Our graphene-CdS NW structures can be useful because they were much faster than commercial CdS film-based photodetectors and had photocurrents large enough for practical applications

Graphene-nanowire hybrid structures for high-performance photoconductive devices

Graphene-CdS nanowire (NW) hybrid structures with high-speed photoconductivity were developed. The hybrid structure was comprised of CdS NWs which were selectively grown in specific regions on a single-layer graphene sheet. The photoconductive channels based on graphene-CdS NW hybrid structures exhibited much larger photocurrents than graphene-based channels and much faster recovery speed than CdS NW network-based ones. Our graphene-CdS NW structures can be useful because they were much faster than commercial CdS film-based photodetectors and had photocurrents large enough for practical applications.open112930sciescopu