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124 results on '"Png, Rui-Qi"'

9. Doped polymer semiconductors with ultrahigh and ultralow work functions for ohmic contacts

Author

Tang, Cindy G., Ang, Mervin C. Y., Choo, Kim-Kian, Keerthi, Venu, Tan, Jun-Kai, Syafiqah, Mazlan Nur, Kugler, Thomas, Burroughes, Jeremy H., Png, Rui-Qi, Chua, Lay-Lay, and Ho, Peter K. H.

Subjects
Semiconductors (Materials) -- Production processes, Conducting polymers -- Production processes, Environmental issues, Science and technology, Zoology and wildlife conservation
Abstract

Author(s): Cindy G. Tang [1, 2]; Mervin C. Y. Ang [2, 3]; Kim-Kian Choo [3]; Venu Keerthi [3]; Jun-Kai Tan [1, 2]; Mazlan Nur Syafiqah [3]; Thomas Kugler [4]; Jeremy [...]

Published
2016
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10. Role of Linker Functionality in Polymers Exhibiting Main‐Chain Thermally Activated Delayed Fluorescence

Author

Philipps, Kai, primary, Ie, Yutaka, additional, van der Zee, Bas, additional, Png, Rui‐Qi, additional, Ho, Peter K. H., additional, Chua, Lay‐Lay, additional, del Pino Rosendo, Esther, additional, Ramanan, Charusheela, additional, Wetzelaer, Gert‐Jan A. H., additional, Blom, Paul W. M., additional, and Michels, Jasper J., additional

Published
2022
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18. Effects of Planarization of the Triphenylamine Unit on the Electronic and Transport Properties of Triarylamine–Fluorene Copolymers in Both Doped and Undoped Forms

Author

Koh, Qi-Mian, Mazlan, Nur Syafiqah, Seah, Qiu-Jing, Yang, Jin-Cheng, Chen, Yue-Jia, Png, Rui-Qi, Ho, Peter K. H., and Chua, Lay-Lay

Abstract

Triarylamine-alt-fluorene (TAF) copolymers are widely used for hole injection and transport in organic electronics. Despite suggestions to planarize the triphenylamine moiety, little research has been conducted. Here, we report a comprehensive investigation of the effects of planarization on the electronic and transport properties of a model TAF polymer semiconductor core. We compared the conventional twisted-propeller N-4-methoxyphenyl-N,N-diphenylamine-4′,4″-diyl (TA) unit and its planarized bridged analogue (bTA) where adjacent o,o′-positions are linked by 1,1-dimethylmethylene. We studied both polyelectrolyte and non-polyelectrolyte forms of this core in both doped and undoped states. We found that planarization leads to an unprecedented trap-free transport of holes, and a pronounced enhancement of their mobility in the undoped state though less so in the doped state. Planarization also induces a slight reduction in the ionization energy of the undoped polymer, consequently lowering the work function of the doped polymer. This is accompanied by small spectral shifts: a red shift in the first absorption band of the undoped polymer and a blue shift in the first absorption band of the polaron. Furthermore, this study unveils new fundamental features of TAF polymers: (i) Doping induces the formation of three polaron bands within the subgap. (ii) Absorption of both neutral and polaron segments exhibit a linear intensity relationship with doping level. (iii) Electrical conductivity reaches a maximum at the half-doped state, varying as σ ∼ (x(1 – x))3for 0.1 ≲ x≲ 0.9, where xis the doping level. Finally, we demonstrate the successful integration of these self-compensated hole-doped TAF polymers as efficient hole injection layers in organic semiconductor diodes.

Published
2024
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20. Low frequency noise analysis on organic thin film transistors.

Author

Ke, Lin, Dolmanan, Surani Bin, Shen, Lu, Vijila, Chellappan, Chua, Soo Jin, Png, Rui-Qi, Chia, Perq-Jon, Chua, Lay-Lay, and Ho, Peter K.-H.

Subjects
ORGANIC thin films, TRANSISTORS, ORGANIC field-effect transistors, SPECTRUM analysis, DIELECTRICS, METAL oxide semiconductor field-effect transistors, MONOMOLECULAR films
Abstract

Bottom-contact organic field-effect transistors (OFETs) based on poly(3-hexylthiophene) with different channel lengths were fabricated under different substrate pretreatment process conditions. These OFET devices were characterized using low frequency noise (LFN) spectroscopy, and the device performance parameters were correlated with the level of LFN. It is observed that the devices with higher noise levels showed poorer device properties when compared with the devices operated at same Ids of the same channel length. It is also observed that the noise level increased with the increase in channel length for devices with the same pretreatment conditions, which is due to increased trapping and detrapping in the channel material interface domain. The OFET device operating around the threshold voltage Vth will have a 1/f noise slope that is flatter, having a gradient that is smaller in magnitude. The threshold voltage of a device can thus be observed to be at the gate voltage in which 1/f noise intensity is the highest at low frequencies. [ABSTRACT FROM AUTHOR]

Published
2008
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23. Solution-processed 2-dimensional hole-doped ionic graphene compounds

Author

Kam, Fong-Yu, primary, Png, Rui-Qi, additional, Ang, Mervin C. Y., additional, Kumar, Pawan, additional, Rubi, Km, additional, Mahendiran, Ramanathan, additional, Solomeshch, Olga, additional, Tessler, Nir, additional, Lim, Geok-Kieng, additional, Chua, Lay-Lay, additional, and Ho, Peter K. H., additional

Published
2017
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27. Influence of Interfacial Area on Exciton Separation and Polaron Recombination in Nanostructured Bilayer All-Polymer Solar Cells

Author

Pfadler, Thomas, primary, Coric, Mihael, additional, Palumbiny, Claudia M., additional, Jakowetz, Andreas C., additional, Strunk, Karl-Philipp, additional, Dorman, James A., additional, Ehrenreich, Philipp, additional, Wang, Cheng, additional, Hexemer, Alexander, additional, Png, Rui-Qi, additional, Ho, Peter K. H., additional, Müller-Buschbaum, Peter, additional, Weickert, Jonas, additional, and Schmidt-Mende, Lukas, additional

Published
2014
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37. Interplay of Processing, Morphological Order, and Charge-Carrier Mobility in Polythiophene Thin Films Deposited by Different Methods: Comparison of Spin-Cast, Drop-Cast, and Inkjet-Printed Films

Author

Wong, Loke-Yuen, primary, Png, Rui-Qi, additional, Silva, F. B. Shanjeera, additional, Chua, Lay-Lay, additional, Repaka, D. V. Maheswar, additional, Gao, Xing-Yu, additional, Ke, Lin, additional, Chua, Soo-Jin, additional, Wee, Andrew T. S., additional, and Ho, Peter K. H., additional

Published
2010
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39. High-performance polymer semiconducting heterostructure devices by nitrene-mediated photocrosslinking of alkyl side chains

Author

Png, Rui-Qi, primary, Chia, Perq-Jon, additional, Tang, Jie-Cong, additional, Liu, Bo, additional, Sivaramakrishnan, Sankaran, additional, Zhou, Mi, additional, Khong, Siong-Hee, additional, Chan, Hardy S. O., additional, Burroughes, Jeremy H., additional, Chua, Lay-Lay, additional, Friend, Richard H., additional, and Ho, Peter K. H., additional

Published
2009
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41. Direct Spectroscopic Evidence for a Photodoping Mechanism in Polythiophene and Poly(bithiophene-alt-thienothiophene) Organic Semiconductor Thin Films Involving Oxygen and Sorbed Moisture

Author

Zhuo, Jing-Mei, primary, Zhao, Li-Hong, additional, Png, Rui-Qi, additional, Wong, Loke-Yuen, additional, Chia, Perq-Jon, additional, Tang, Jie-Cong, additional, Sivaramakrishnan, Sankaran, additional, Zhou, Mi, additional, Ou, Eric C.-W., additional, Chua, Soo-Jin, additional, Sim, Wee-Sun, additional, Chua, Lay-Lay, additional, and Ho, Peter K.-H., additional

Published
2009
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48. A High-Performance p-Doped Conducting PolymerBlend Based on Sulfonated Polyalkoxythiophene and Poly(4-hydroxystyrene).

Author

Belaineh, Dagmawi, Png, Rui-Qi, McGuiness, Christine L., Mathai, Mathew, Seshadri, Venkataramanan, and Ho, Peter K. H.

Subjects
*DOPING agents (Chemistry), *POLYMER blends, *CONDUCTING polymers, *SULFONATION, *POLYTHIOPHENES, *POLYSTYRENE
Abstract

Understanding the fundamental mechanismsof electrical degradationor instability in organic semiconductor devices is a key step towardtheir rational design for higher performance and more demanding applications.Here we report the successful suppression of the conductivity fadephenomenon that occurs in doped conducting polymers when they arestress-biased with a large electric field or current density. Whilepoly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDT:PSSH)shows a relatively low threshold to conductivity fading, the recentlydeveloped sulfonated poly{thiophene-3-[2-(2-methoxyethoxy)ethoxy]-2,5-diyl}:poly(4-hydroxystyrene)(S-P3MEET:PHOST), which is an intimate blend of S-P3MEET and PHOST,is far more resilient. In situUV–vis, Raman,and Fourier-transform infrared spectroscopies reveal that the dopinglevel across S-P3MEET:PHOST films remains remarkably stable when theyare driven at high dc biases. Spectroelectrochemical Raman measurementssuggest that both S-P3MEET and S-P3MEET:PHOST are also less susceptibleto electrochemical dedoping than PEDT:PSSH. Comparison of the conductivityfading characteristics of S-P3MEET in the presence or absence of PHOST,however, reveals a large matrix effect. We obtained evidence thatthe enhanced electrical stability of S-P3MEET:PHOST results from itsinherent ultralow ionic conductivity, further suppressed by a serendipitousscavenging of excess sulfonic acid protons on S-P3MEET through a solid-stateesterification reaction with PHOST during annealing. The shutdownof the ionic conductivity cuts off the coupled ion transfer processesneeded to cause a doping level shift in the film. This affords a practicalmeans of suppressing the electrically induced doping level instabilityin doped conducting polymer systems. [ABSTRACT FROM AUTHOR]

Published
2014
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49. Evaluation of Built-In Potential and Loss Mechanisms at Contacts in Organic Solar Cells: Device Model Parameterization, Validation, and Prediction.

Author

Liu, Bo, Png, Rui‐Qi, Tan, Jun‐Kai, and Ho, Peter K. H.

Subjects
*SOLAR cell efficiency, *PHOTOVOLTAIC cells, *HYBRID solar energy systems, *PARAMETERIZATION, *STRUCTURAL optimization
Abstract

Maximizing the power conversion efficiency of organic solar cells requires the simultaneous optimization of its short-circuit current density, fill factor, and open-circuit voltage Voc. Several key parameters of the device model needed to understand these quantities have not been reliably determined, even for the prototypical poly(3-hexylthiophene):phenyl-C61-methylbutyric ester (P3HT:PCBM) photoactive layer (PAL). Detailed analysis of the loss mechanisms at contacts and their rational optimization have not been possible. Here, using crosslinked P3HT network:PCBM cells with predefined ultrafine donor-acceptor morphology and very high internal quantum efficiencies, the built-in potential Vbi is measured to decouple and reliably extract other key parameters of the cells. Using the refined device parameters, the general optimization of organic solar cells is evaluated and the following is established: i) The PAL composition of the first optical absorption optimum is displaced towards the more strongly absorbing component due to thin film effects. ii) The optimal cell configuration is the one in which the slower carrier travels on average the shorter distance to the collection contact, a consequence of the asymmetric photogeneration profile. iii) The absorption thickness optima follows a simple λp/ nPAL scaling law, where λp is its absorption center wavelength and nPAL is the corresponding refractive index. [ABSTRACT FROM AUTHOR]

Published
2014
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50. Evidence for Morphology Control by Polyelectrolyte Templating in PEDT:PSSH.

Author

Koh, Qi‐Mian, Seah, Qiu‐Jing, Yang, Jin‐Cheng, Mazlan, Nur Syafiqah, Hoh, Quan‐En, Seah, Zong‐Long, Png, Rui‐Qi, Ho, Peter K.H., and Chua, Lay‐Lay

Subjects
*SURFACE segregation, *ELECTRIC conductivity, *MORPHOLOGY, *ION exchange (Chemistry), *CONDUCTING polymers, *OPTICAL properties
Abstract

Despite decades of research, the fundamental question of structure and morphology of the poly(3,‐4‐ethylenedioxythiophene):poly(styrene sulfonate) complex (PEDT: PSS) electrically conducting polymer remains open. Here, through a systematic study of the polymerization of 3,4‐ethylenedioxythiophene (EDT) on two series of sulfonated polystyrenes, i.e., PS‐co‐SSH and PS‐co‐SSNa, with per cent sulfonation 24 ≲ x ≲ 100, this study shows that the substrate polyelectrolyte not only affords charge compensation and processability, but also templates the morphology of the growing PEDT chain—whether extended, coiled or collapsed. This determines the electrical, electronic and optical properties of the resultant PEDT: PSS interpolyelectrolyte complexes, including their work function. This study calls this the Polyelectrolyte Template model. The PEDT: PSS complex retains memory of its polymerization morphology even after subsequent ion‐exchange, for example, to the same acid form. Electrical conductivity decreases sharply with decreasing x, and depends on whether the polymerization is templated with the H+ or Na+ form of the polyelectrolyte. The work function is less sensitive to x, but exhibits a transition from low to high work function (5.2–5.3 eV) when x exceeds a threshold, which indicates formation of a polar surface driven by molecular‐scale segregation of the PSS counteranion. This surface segregation also affects the ability of these complexes to inject holes into very large‐ionization‐energy semiconductors. [ABSTRACT FROM AUTHOR]

Published
2024
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