Browsing by Author "Kuo, Chih-Yin"

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An Organic Hole Transport Layer Enhances the Performance of Colloidal PbSe Quantum Dot Photovoltaic Devices
(2010-10-22)
Kuo, Chih-Yin
;
Su, Ming-Shin
;
Hsu, Yu-Chien
;
Lin, Hui-Ni
;
Wei, Kung-Hwa
A thin poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) hole transport layer enhances the AM1.5 power conversion efficiency of a PbSe quantum dot (QD)-containing photovoltaic device to 2.4%, from 1.5% for a standard PbSe QD device, a relative increase of 60%. Synchrotron X-ray reflectivity measurements reveal that the roughness of the interfaces between the various layers decreases dramatically in the presence of the PEDOT: PSS layer. In addition, the device life time under continuous simulated AM1.5 irradiation (100 mW cm(-2)), measured in terms of the time required to reach 80% of the normalized efficiency, for the PbSe QD device incorporating the PEDOT:PSS hole transport layer is six times longer than that of the standard PbSe QD device.
An Organic Hole Transport Layer Enhances the Performance of Colloidal PbSe Quantum Dot Photovoltaic Devices
(2010-10-22)
Kuo, Chih-Yin
;
Su, Ming-Shin
;
Hsu, Yu-Chien
;
Lin, Hui-Ni
;
Wei, Kung-Hwa
A thin poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) hole transport layer enhances the AM1.5 power conversion efficiency of a PbSe quantum dot (QD)-containing photovoltaic device to 2.4%, from 1.5% for a standard PbSe QD device, a relative increase of 60%. Synchrotron X-ray reflectivity measurements reveal that the roughness of the interfaces between the various layers decreases dramatically in the presence of the PEDOT: PSS layer. In addition, the device life time under continuous simulated AM1.5 irradiation (100 mW cm(-2)), measured in terms of the time required to reach 80% of the normalized efficiency, for the PbSe QD device incorporating the PEDOT:PSS hole transport layer is six times longer than that of the standard PbSe QD device.
Annealing treatment improves the morphology and performance of photovoltaic devices prepared from thieno[3,4-c]pyrrole-4,6-dione-based donor/acceptor conjugated polymers and CdSe nanostructures
(2011-06-01)
Kuo, Chih-Yin
;
Su, Ming-Shi
;
Chen, Guan-Yu
;
Ku, Ching-Shun
;
Lee, Hsin-Yi
We have prepared photovoltaic devices based on blend films of CdSe tetrapods and the donor/acceptor conjugated polymer PDTTTPD, which comprises 2,5-di(thiophen-2-yl) thieno[3,2-b]thiophene and thieno[3,4-c]pyrrole-4,6-dione units. The AM1.5 power conversion efficiency (PCE) of a photovoltaic device containing a PDTTTPD/CdSe tetrapod blend (1:9, w/w) that had experienced thermal annealing (130 degrees C, 20 min) was three times greater than that of the corresponding device incorporating the as-prepared PDTTTPD/CdSe tetrapod blend (2.9% vs. 1.0%). Synchrotron X-ray reflectivity revealed that annealing (i.e., removal of pyridine ligands from the surfaces of the CdSe tetrapods) caused the thickness of the PDTTTPD/CdSe tetrapod blend film to decrease (and its average density to increase) relative to that of the as-prepared blend film. Transmission electron microscopy and atomic force microscopy revealed that thermal annealing enhanced the degree of aggregation of the CdSe tetrapods and induced denser morphologies, leading to substantially increased charge transport, which enhanced the PCE of the device.
Improving Device Efficiency of Polymer/Fullerene Bulk Heterojunction Solar Cells Through Enhanced Crystallinity and Reduced Grain Boundaries Induced by Solvent Additives
(2011-08-02)
Su, Ming-Shin
;
Kuo, Chih-Yin
;
Yuan, Mao-Chuan
;
Jeng, U-Ser
;
Su, Chun-Jen
The power conversion efficiency of a device incorporating a crystalline polymer/fullerene thin film improves from 5% to 7.3% - a relative increase of 45% - when an additive, diiodohexane (DIH), is present during processing. The DIH-processed active layer exhibits substantially enhanced polymer crystallinity and smaller fractal-like fullerene clusters.
In situ electrochemical doping enhances the efficiency of polymer photovoltaic devices
(2011)
Su, Ming-Shin
;
Su, Hai-Ching
;
Kuo, Chih-Yin
;
Zhou, Yi-Ren
;
Wei, Kung-Hwa
In this study, we found that the formation of a p-i-n junction through in situ electrochemical doping is a promising way to enhance the performance of polymer photovoltaic devices. We applied a pre-bias to metal triflate [LiOTf, KOTf, Ca(OTf)(2), Zn(OTf)(2)]/poly(ethylene oxide) (PEO)-incorporated poly[5-(2'-ethylhexyloxy)-2-methoxy-1,4-phenylenevinylene] (MEH-PPV)/{6}-1-(3-(methoxycarbonyl) propyl)-{5}-1-phenyl-[5,6]-C(61) (PCBM) photovoltaic devices to form p-i-n junctions in their active layers. Auger depth profile analyses and alternating-current capacitance analyses of these doped devices revealed that the positive and negative ions were distributed unequally to form an asymmetrical p-i-n structure in a thin layer of ca. 100 nm of the polymer, and the intrinsic layer became thinner when formed under a higher pre-bias voltage. Atomic force microscopy and transmission electron microscopy revealed that the addition of metal triflate/PEO to MEH-PPV/PCBM improved the morphology of the composite films. Among the various doped devices, the MEH-PPV/PCBM device incorporating a LiOTf/PEO mixture exhibited the highest power conversion efficiency, a 40% increase relative to that of the reference device (MEH-PPV/PCBM).
Ligands affect the crystal structure and photovoltaic performance of thin films of PbSe quantum dots
(2011)
Kuo, Chih-Yin
;
Su, Ming-Shin
;
Ku, Ching-Shun
;
Wang, Shu-Min
;
Lee, Hsin-Yi
We have prepared thin films of PbSe quantum dots (QDs) featuring three different ligands, oleic acid (OA), butylamine (BA), and 1,2-ethanedithiol (EDT), which have pronounced affects on the arrangement and photovoltaic performance of the PbSe QDs in the thin films. Transmission electron microscopy revealed that ligands that altered the inter-QD spacing induced significant changes in the packing of the PbSe QDs in localized regions of small areas (300 x 300 nm) of the thin films: from a superlattice of OA-capped PbSe QDs to a chaotic pattern of EDT-capped PbSe QDs. Using a synchrotron X-ray reflectivity probe and data fitting, we determined that the roughness decreased and the average densities increased for large-area (1.5 x 1.5 cm) PbSe QD thin films capped with BA and EDT, relative to those of the OA-capped PbSe QD film. In particular, the PbSe QDs' vertical packing density, which is critical for charge transport, increased substantially for the system incorporating EDT ligands. As a result, devices containing the EDT-treated PbSe QD film as the active layer displayed much improved power conversion efficiencies (PCEs) relative to those of corresponding devices featuring either the OA-or BA-capped PbSe QD films as active layers. Adopting a layer-by-layer technique, we fabricated a EDT-capped PbSe QD device that exhibited a PCE of 2.45%.