Browsing by Author "Chang, Jan-Kai"

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13% Efficiency Hybrid Organic/Silicon-Nanowire Heterojunction Solar Cell via Interface Engineering
(2013-12-01)
Yu, Peichen
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Tsai, Chia-Ying
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Chang, Jan-Kai
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Lai, Chih-Chung
;
Chen, Po-Han
Interface carrier recombination currently hinders the performance of hybrid organic silicon heterojunction solar cells for high-efficiency low-cost photovoltaics. Here, we introduce an intermediate 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAP() layer into hybrid heterojunction solar cells based on silicon nanowires (SINWs) and conjugate polymer poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS). The highest power conversion efficiency reaches a record 13.01%, which is largely ascribed to the modified organic surface morphology and suppressed saturation current that boost the open-circuit voltage and fill factor. We show that the insertion of TAP( increases the minority carrier lifetime because of an energy offset at the heterojunction interface. Furthermore, X-ray photoemission spectroscopy reveals that TAP( can effectively block the strong oxidation reaction occurring between PEDOT:PSS and silicon, which improves the device characteristics and assurances for reliability. These learnings point toward future directions for versatile interface engineering techniques for the attainment of highly efficient hybrid photovoltaics.
Bridging donor-acceptor energy offset using organic dopants as energy ladders to improve open-circuit voltages in bulk-heterojunction solar cells
(2014-12-01)
Chang, Jan-Kai
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Kuo, Ya-Ching
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Chen, Yu-Jen
;
Lo, An-Lun
;
Liu, I-Hsiu
A systematic way to improve the open circuit voltage of bulk-heterojunction (BHJ) organic photovoltaics is demonstrated by incorporating energy ladder material to form a ternary blend with cascade energy structures. We propose that doping organic molecules with appropriate energetic alignment to bridge the donor-acceptor energy offset can facilitate exciton dissociation and hence improve open-circuit voltage (V-oc) and power conversion efficiency. The cascade energy alignment structure is measured via ultraviolet photoemission spectroscopy. The Voc and power conversion efficiency of devices using the proposed schemes can be enhanced by 10% and 20%, respectively. The results provide a new path toward higher power conversion efficiency in BHJ systems by engineering the energy structures of the materials in the active layers. (C) 2014 Elsevier B.V. All rights reserved.
Effects on Organic Photovoltaics Using Femtosecond-Laser-Treated Indium Tin Oxides
(2016-09-28)
Chen, Mei-Hsin
;
Tseng, Ya-Hsin
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Chao, Yi-Ping
;
Tseng, Sheng-Yang
;
Lin, Zong-Rong
The effects of, femtosecond-laser-induced periodic surface structures (LIPSS) on an indium tin oxide (ITO) surface applied to an organic photovoltaic (OPV), system were investigated. The modifications of ITO induced by LIPPS in OPV devices result in more than 14% increase in power conversion efficiency (PCE) and short-circuit current density relative to-those of the standard device. The basic mechanisms for the enhanced short-circuit current density are attributed to better light harvesting, increased scattering effects, and more efficient charge collection between the ITO and photoactive layers: Results show that-higher PCEs would be achieved by laser-pulse-treated electrodes.
Monolayer MoSe2 Grown by Chemical Vapor Deposition for Fast Photodetection
(2014-08-01)
Chang, Yung-Huang
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Zhang, Wenjing
;
Zhu, Yihan
;
Han, Yu
;
Pu, Jiang
Monolayer molybdenum disulfide (MoS2) has become a promising building block in optoelectronics for its high photosensitivity. However, sulfur vacancies and other defects significantly affect the electrical and optoelectronic properties of monolayer MoS2 devices. Here, highly crystalline molybdenum diselenide (MoSe2) monolayers have been successfully synthesized by the chemical vapor deposition (CVD) method. Low-temperature photoluminescence comparison for MoS2 and MoSe2 monolayers reveals that the MoSe2 monolayer shows a much weaker bound exciton peak; hence, the phototransistor based on MoSe2 presents a much faster response time (<25 ms) than the corresponding 30 s for the CVD MoS2 monolayer at room temperature in ambient conditions. The images obtained from transmission electron microscopy indicate that the MoSe exhibits fewer defects than MoS2. This work provides the fundamental understanding for the differences in optoelectronic behaviors between MoSe2 and MoS2 and is useful for guiding future designs in 2D material-based optoelectronic devices.
Monolayer MoSe2 Grown by Chemical Vapor Deposition for Fast Photodetection
(2014-08-01)
Chang, Yung-Huang
;
Zhang, Wenjing
;
Zhu, Yihan
;
Han, Yu
;
Pu, Jiang
Monolayer molybdenum disulfide (MoS2) has become a promising building block in optoelectronics for its high photosensitivity. However, sulfur vacancies and other defects significantly affect the electrical and optoelectronic properties of monolayer MoS2 devices. Here, highly crystalline molybdenum diselenide (MoSe2) monolayers have been successfully synthesized by the chemical vapor deposition (CVD) method. Low-temperature photoluminescence comparison for MoS2 and MoSe2 monolayers reveals that the MoSe2 monolayer shows a much weaker bound exciton peak; hence, the phototransistor based on MoSe2 presents a much faster response time (<25 ms) than the corresponding 30 s for the CVD MoS2 monolayer at room temperature in ambient conditions. The images obtained from transmission electron microscopy indicate that the MoSe exhibits fewer defects than MoS2. This work provides the fundamental understanding for the differences in optoelectronic behaviors between MoSe2 and MoS2 and is useful for guiding future designs in 2D material-based optoelectronic devices.
Rear interface engineering of hybrid organic-silicon nanowire solar cells via blade coating
(2016-01-25)
Lai, Yi-Chun
;
Chang, Yu-Fan
;
Tsai, Pei-Ting
;
Chang, Jan-Kai
;
Tseng, Wei-Hsuan
In this work, we investigate blade-coated organic interlayers at the rear surface of hybrid organic-silicon photovoltaics based on two small molecules: Tris(8-hydroxyquinolinato) aluminium (Alq(3)) and 1,3-bis(2-(4-tert- butylphenyl)-1,3,4-oxadiazol-5-yl) benzene (OXD-7). In particular, soluble Alq3 resulting in a uniform thin film with a root-mean-square roughness < 0.2nm is demonstrated for the first time. Both devices with the Alq3 and OXD-7 interlayers show notable enhancement in the open-circuit voltage and fill-factor, leading to a net efficiency increase by over 2% from the reference, up to 11.8% and 12.5% respectively. The capacitance-voltage characteristics confirm the role of the small-molecule interlayers resembling a thin interfacial oxide layer for the Al-Si Schottky barrier to enhance the built-in potential and facilitate charge transport. Moreover, the Alq3 interlayer in optimized devices exhibits isolated phases with a large surface roughness, in contrast to the OXD-7 which forms a continuous uniform thin film. The distinct morphological differences between the two interlayers further suggest different enhancement mechanisms and hence offer versatile functionalities to the advent of hybrid organic-silicon photovoltaics. (C)2016 Optical Society of America