1,721,013 research outputs found
Modeling the electrical characteristics of TIPS-pentacene thin-film transistors: Effect of contact barrier, field-dependent mobility, and traps
No full textThe device characteristics of organic thin-film transistors (OTFT) fabricated using tris-isopropylsilylethynyl (TIPS)-pentacene are analyzed with the help of a two-dimensional physics-based numerical simulation. The model incorporates contact barrier at a metal-semiconductor interface, field-dependent mobility, and trap distribution in TIPS-pentacene films and at dielectric-semiconductor interface. The Poole-Frenkel type field-dependence of mobility is included in addition to the contact barrier height of 0.38 eV to describe the non-ideal behavior in the linear region of the output characteristics. An account of the transfer characteristics and its hysteresis behavior is completed in both below- and above-threshold region upon consideration of the presence of acceptor-like traps of an exponential distribution in TIPS-pentacene films and positive trapped charges at dielectric-semiconductor interface. The obtained device parameters not only match the electrical characteristics but also give one an insight on the charge injection, transport, and trap properties of TIPS-pentacene from the perspectives of TFT operation. (C) 2008 Elsevier B.V. All rights reserved
Impact of non-fullerene acceptors and solvent additive on the nanomorphology, device performance, and photostability of PTB7-Th polymer based organic solar cells
No full textNon-fullerene acceptors have recently ignited extensive interest in organic solar cells (OSCs) because of their higher power conversion efficiency (PCE) than their fullerene counterparts. Though the effect of solvent additive 1, 8-diiodooctane (DIO) has been studied extensively for fullerene-based acceptor OSCs, not much is known for non-fullerene acceptors OSCs. In our work, bulk-heterojunction (BHJ) OSCs were fabricated by blending fullerene (PC71BM) and non-fullerene (ITIC and IEICO-4F) acceptors with low bandgap polymer donor (PTB7-Th). Further, the effects of non-fullerene acceptors on the nanomorphology, performance, and photostability of the devices were investigated. In the absence of DIO, devices with IEICO-4F acceptor showed higher PCE than PTB7-Th: ITIC and PTB7-Th: PC71BM BHJ-OSCs due to their absorption in near infrared along with high J (sc). The addition of DIO increased PCE in PTB7-Th: PC71BM BHJ-OSCs due to improved miscibility of fullerene molecules, higher donor/acceptor interface area, and improved phase separation. However, DIO adversely affected the overall device performance in PTB7-Th: IEICO-4F and PTB7-Th: ITIC BHJ-OSCs. Furthermore, devices processed with DIO were less photostable and exhibited faster degradation due to the photoacid effect of the DIO additive.
Electrical-Stress-Induced Threshold Voltage Instability in Solution-Processed ZnO Thin-Film Transistors: An Experimental and Simulation Study
No full textIn this paper, we present the experimental and simulation results of the stress-recovery characteristics of solution-processed ZnO thin-film transistors under gate bias and current stress conditions. Under both stress conditions, we invariably observed a positive threshold voltage shift (Delta V(T)) that is initially associated with changes in the values of subthreshold slope and off-current, which later becomes constant on prolonging the stress time. However, Delta V(T) was less for current stress, compared with gate bias stress. This stress-induced Delta V(T) is speculated to be caused by defect creation in the active layer and charge trapping at the semiconductor-dielectric interface. Following a stretched exponential model, at room temperature, a characteristics time of 1.6 x 10(3) -3.6 x 10(3) s during stress and 7.7 x 10(3) -15.7 x 10(3) s during recovery was obtained under all gate bias and current stress conditions. The Delta V(T)-time measurements performed under various temperatures yield an activation energy of similar to 0.5 and similar to 0.7 eV for the stress and recovery periods, respectively. The device simulation indicates that Delta V(T) is mainly caused by the increase in acceptorlike defects of the density of states in the ZnO channel layer. Furthermore, it was found that the deep lying states are responsible for the change in the value of inverse subthreshold slope
Combined effect of ZnO nanoripples and solvent additive on the nanomorphology and performance of PTB7-Th: PC71BM organic solar cells
No full textIn bulk heterojunction organic solar cells (OSCs), nanomorphology of the photoactive layer plays a crucial role in determining photocurrent and fill factor (FF) of OSCs, and therefore it is essential to control the nanomorphology of the photoactive layer to fabricate devices with high power conversion efficiency (PCE). We demonstrate the combined effects of a ZnO nanorippled electron transport layer (ETL) and solvent additive (1,8-diiodooctane (DIO)) on the nanomorphology and performance of a model OSC in an inverted geometry. The photoactive layer in the model OSC is composed of Poly [4,8-bis (5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3- fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl] (PTB7-Th):phenyl-C71-butyric acid methyl ester (PC71BM) blend. It is observed that the use of ZnO nanoripples as an ETL and DIO as a solvent additive facilitates the formation of near ideal nanomorphology of bi-continuous interpenetrating network of donor and acceptor. This is confirmed by morphological studies using atomic force microscopy, scanning electron microscopy and transmission electron microscopy. Photo-electrochemical impedance spectroscopy measurements confirm that obtained nanomorphology of bicontinuous interpenetrating network is contributing to the improved device performance. The device with 3 vol% DIO, with underneath ZnO nanoripples exhibited improved current density (J(sc)), FF, open circuit voltage (V-oc) and PCE of 15.57 mA cm(-2), 64.50%, 0.81V and 8.20%, respectively.
Nonvolatile memory based on sol-gel ZnO thin-film transistors with Ag nanoparticles embedded in the ZnO/gate insulator interface
No full textA nonvolatile memory is demonstrated using a solution-processed sol-gel ZnO thin-film transistor (TFT) in which Ag nanoparticles are embedded as charge storage nodes at the insulator-ZnO interface. Its TFT transfer characteristics exhibit a large clockwise hysteresis that is proportional to the gate bias sweep range. Measurement of the threshold voltage shift versus the pulse width of gate bias reveals that the device can be programed or erased at a time scale of as short as 10(-4) s. Retention of the initial memory window is measured to be 27% after 10(5) s and projected to last until 10(7) s
Charge carrier dynamics in PffBT4T-2OD: PCBM organic solar cells
No full textWe investigate the charge carrier dynamics of inverted organic solar cells (OSCs) based on PffBT4T-2OD: PCBM and PTB7: PCBM - the two leading systems among the OSCs based on polymer-fullerene bulk-heterojunction - to elucidate the origin of their performance difference. Transient absorption spectroscopy (TAS) and photo-electrochemical impedance spectroscopy (photo-EIS) were employed to unravel the photo-physics that govern the cell operation of these two highly efficient bulk heterojunction OSCs. While photo-EIS indicates that the two systems under study exhibit similar behavior in terms of recombination, TAS results reveal that PffBT4T-2OD: PCBM systems not only have higher charge generation rate but also more efficient charge transfer than PTB7: PCBM systems, leading to the power conversion efficiency of PffBT4T-2OD: PCBM-based OSCs (9.16%) that is higher than that of PTB7: PCBM-based OSCs (6.44%).
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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