Browsing by Author "Wang, Pen-Cheng"

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Asymmetric Benzotrithiophene-Based Hole Transporting Materials Provide High-Efficiency Perovskite Solar Cells
(2020-07-01)
Budiawan, Widhya
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Lai, Kuan-Wen
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Karuppuswamy, Priyadharsini
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Jadhav, Tushar Sanjay
;
Lu, Yen-An
In this study, we synthesized a series of small-molecule benzotrithiophenes (BTTs) and used them as hole transporting materials (HTMs) in perovskite solar cells (PSCs). The asymmetric benzo[2,1-b:-3,4-b':5,6-b"]trithiophene unit was used as the central core to which were appended various donor groups, namely, carbazole (BTT-CB), thieno thiophene (BTT-FT), triphenylamine (BTT-TPA), and bithiophene (BTT-TT). The extended aromatic core in the asymmetric BTT provided full planarity, thereby favoring intermolecular pi-stacking and charge transport. The physical, optical, and electrical properties of these small-molecule HTMs are reported herein. BTT-TT displayed good crystallinity and superior hole mobility, when compared with those of the other three HTMs, and formed smooth and uniform surfaces when covering the perovskite active layer. Accordingly, among the devices prepared in this study, a PSC incorporating BTT-TT as the HTM achieved the highest power conversion efficiency (18.58%). Moreover, this BTT-TT-containing device exhibited good stability after storage for more than 700 h. Thus, asymmetric BTTs are promising candidate materials for use as small-molecule HTMs in PSCs.
Effect of molecular weight of additives on the conductivity of PEDOT: PSS and efficiency for ITO-free organic solar cells
(2013)
Mengistie, Desalegn Alemu
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Wang, Pen-Cheng
;
Chu, Chih-Wei
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光電工程學系
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Department of Photonics
We systematically investigated the effect of the molecular weight of additives on the conductivity of poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) by using different concentrations and molecular weights of polyethylene glycol (PEG) and ethylene glycol (EG). The conductivity enhancement depends on both the molecular weight and concentration of PEG used. The conductivity of PEDOT: PSS was enhanced from 0.3 S cm(-1) to 805 S cm(-1) with 2% PEG but to only 640 S cm(-1) with 6% EG. PEGs with molecular weight higher than 400 have too low mobility to impart the required screening effect, and hence, the conductivity enhancement is less. Through FTIR, XPS and AFM investigations, the mechanism for the conductivity enhancement is found to be charge screening between PEDOT and PSS followed by phase separation and reorientation of PEDOT chains leading to bigger and better connected particles. The molecular weight and concentration of PEG also affect solar cell performances even though the conductivities are the same. Due to their high conductivity and high transmittance, ITO-free organic solar cell devices fabricated using PEDOT: PSS treated with 2% PEG anodes exhibited performance almost equal to that of the ITO counterparts.
Enhanced Organic Solar Cell Performance by Lateral Side Chain Engineering on Benzodithiophene-Based Small Molecules
(2018-08-01)
Patra, Dhananjaya
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Budiawan, Widhya
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Huang, Tzu-Yen
;
Wei, Kung-Hwa
;
Wang, Pen-Cheng
The three novel acceptor-donor-acceptor (A-D-A) conjugated small molecules were synthesized, each featuring a benzodithiophene (BDT) core presenting lateral flexible side chains: TB-BDT6T substituted with 2-ethynyl-5-octylthiophene, TS-BDT6T substituted with 2-(octylthio)-thiophene, and TT-BDT6T substituted with 2-(2-ethylhexyl)-thieno[3,2-b]thiophene groups. The lateral incorporation of functionalized pi-conjugated flexible side chains, without altering the end-capped acceptor (cyanoacetate) moieties, amended the optoelectronic properties of these BDT-based small molecules. X-ray diffraction spectroscopy revealed that these small molecules possess high crystallinity; moreover, the optimized blend film morphologies, recorded using atomic force microscopy, revealed miscibility with PC61BM, and turn out nanoscale phase separations. The energy levels of the highest occupied and lowest unoccupied molecular orbitals of these small molecules were allowed, leading to high open-circuit voltages (V-oc) for their solar cell devices. The bulk heterojunction small-molecule solar cell based on TT-BDT6T:PC61BM blend presented the highest power conversion efficiency (5.80%) with a high value of V-oc of 0.98 V, a short circuit density of 9.49 mA cm(-2), and a fill factor of 62.44% under AM 1.5G irradiation (100 mW cm(-2)).
Highly Conductive PEDOT:PSS Electrode Treated with Polyethylene Glycol for ITO-free Polymer Solar Cells
(2013)
Mengistie, Desalegn Alemu
;
Wang, Pen-Cheng
;
Chu, Chih-Wei
;
光電工程學系
;
Department of Photonics
We used polyethylene glycol (PEG) and enhanced the conductivity of PEDOT:PSS from 0.3 S cm(-1) to 805 S cm(-1) with only 2% PEG additive. The conductivity was further enhanced to 1100 S cm-1 by combining PEG and methanol treatment. PEG treated PEDOT: PSS films showed better phase separation between PEDOT and PSS with fiber like 3D PEDOT networks. The carrier concentration increased by three orders of magnitude after PEG treatment. ITO-free polymer solar cells with PEG treated PEDOT: PSS anodes were fabricated and optimized. Double layer PEDOT: PSS treated with 2% PEG200 anodes showed power conversion efficiency of 3.71% while and the ITO counterpart showed 3.73%.
Highly Conductive PEDOT:PSS Treated with Formic Acid for ITO-Free Polymer Solar Cells
(2014-02-26)
Mengistie, Desalegn A.
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Ibrahem, Mohammed A.
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Wang, Pen-Cheng
;
Chu, Chih-Wei
;
光電工程學系
We proposed a facile film treatment with formic acid to enhance the conductivity of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) by 4 orders of magnitude. The effect of formic acid concentration on conductivity was investigated; conductivity increased fast with increasing concentration up to 10 M and then increased slightly, the highest conductivity being 2050 S cm(-1) using 26 M concentration. Formic acid treated PEDOT:PSS films also exhibited very high transmittances. The mechanism of conductivity enhancement was explored through SEM, AFM, and XPS. Formic acid with its high dielectric constant screens the charge between PEDOT and PSS bringing about phase separation between them. Increased carrier concentration, removal of PSS from the film, morphology, and conformation change with elongated and better connected PEDOT chains are the main mechanisms of conductivity enhancement. ITO-free polymer solar cells were also fabricated using PEDOT:PSS electrodes treated with different concentrations of formic acid and showed equal performance to that of ITO electrodes. The concentrated acid treatment did not impair the desirable film properties as well as stability and performance of the solar cells.
Transparent electrodes based on conducting polymers for display applications
(2013-10-01)
Wang, Pen-Cheng
;
Liu, Li-Hung
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Mengistie, Desalegn Alemu
;
Li, Kuan-Hsun
;
Wen, Bor-Jiunn
The materials science and engineering related to the fabrication of conducting polymer thin films and the progress in the development of devices integrated with organic transparent electrodes based on conducting polymers for display applications are reviewed. Transparent electrodes are essential components for many display modules. With the evolution of display technologies, conducting polymers are recently emerging as important alternative materials for the fabrication of transparent electrodes. Conducting polymers offer some advantages, such as light weight, low cost, mechanical flexibility and excellent compatibility with plastic substrates for the development of next-generation display technologies and, in particular, are expected to play an important role in the development of flexible display technologies. (C) 2013 Elsevier B.V. All rights reserved.