Browsing by Author "Lan, Yu-Bing"

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Origins of vertical phase separation in P3HT:PCBM mixed films
(2014-04-01)
Liu, I-Hsiu
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Chao, Yi-Ping
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Fang, Jian-Jhih
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Tseng, Wei-Hsuan
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Lan, Yu-Bing
The origins of vertical phase separation and their implication on the device efficiency of poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methyl ester (P3HT:PCBM) based solar cells, with both regular and inverted structures, were investigated. We found that the light irradiation and the filtration processes during the device fabrications are two key steps that induce the vertical phase separation in the active layers. Upon light irradiation, the devices with inverted structures exhibit improved power conversion efficiency, whereas the regular devices show degradation. The inverted devices spun cast with filtered P3HT:PCBM solution also present a better improvement as compared to regular devices. X-ray and ultraviolet photoemission spectroscopies indicate that both illumination and filtration enhance the vertical phase separation of the blend film with additional PCBM segregated to the bottom interface. (C) 2014 The Japan Society of Applied Physics
Polymer side-chain substituents elucidate thermochromism of benzodithiophene-dithiophenylacrylonitrile copolymers - polymer solubility correlation of thermochromism and photovoltaic performance
(2017-06-28)
Chen, Hung-Yang
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Lin, Chiao-Wen
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Chen, Chin-Ti
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Chen, Chao-Tsen
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Golder, Jan
Nine pBCNx polymers based on a donor-p-acceptor benzo[1,2-b:4,5-b']dithiophene-(E)-2,3-di(thiophen-2-yl) acrylonitrile main-chain structure and n-octyl/2-ethylhexyl as the side-chain substituents have been designed and synthesized. The thermochromism of the pBCNx polymers has been carefully examined in both solution and the thin-film state. With additional evidences from Raman spectroscopy and AFM microscopy, we have deciphered the varied colours of nine pBCNx polymers in solution and the pronounced thin-film thermochromism only observed for certain pBCNx polymers, i.e., pBCN4, pBCN5, pBCN6, and pBCN8. The alkyl side-chain, and hence the solubility or aggregation of pBCNx polymers, is a main factor of the varied colour in solution and the varied thermochromism in the thin film. We have identified that a stronger main-chain and main-chain interaction are present on the (E)-2,3-di(thiophen-2-yl) acrylonitrile moiety, whereas the poor to moderate solubility pBCN3, pBCN5', and pBCN7 exhibit pronounced thermochromism in solution, and pBCN4, pBCN5, pBCN6, and pBCN8 are four polymers which have good solubility in solution and show thermochromism in the thin-film state. We took navy blue pBCN3 (poor solubility), magenta pBCN4 (good solubility), and reddish purple pBCN5' (moderate solubility) for the fabrication of bulk heterojunction organic photovoltaics (OPVs). With a solvent annealing treatment, the power conversion efficiency of the OPVs has been improved significantly from 4.7% to 6.2% for the good solubility pBCN4, but there is little and no improvement for the moderate solubility pBCN5' and poor solubility pBCN3, respectively. Our study verifies that the good OPV performance of the pBCNx polymers can be correlated to the pronounced thin-film thermochromism. A good solubility of the polymer is a common characteristic of a material with significant thin-film thermochromism and good OPV performance.
Unconventional anode interlayer universally improving solar cell efficiency
(2018-08-08)
Golder, Jan
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Lin, Chiao-Wen
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Chen, Huan-Wen
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Lan, Yu-Bing
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Chen, Chin-Ti
Organic photovoltaic cells typically employ an interlayer sandwiched between the active donor or acceptor materials and the respective electrodes. Conventionally, the employed anode interlayer (AIL) adjacent to the anode has a wide optical band gap and a significantly higher lowest unoccupied molecular orbital (LUMO) energy level, compared to the adjunct electron donor material, such as boron subphthalocyanine chloride (SubPc) studied here. In this report, we synthesized three novel AIL materials, NP-beta-PCN, NPAPMLI and NPAPMLI, having narrow optical band gaps but matching the LUMO energy levels of SubPc in a planar heterojunction solar cell of ITO/SubPc/C-60/BCP/Al. Upon insertion of an ultrathin (2 nm) AIL, the device power conversion efficiency is increased from 3.98% to as high as 4.92%, mainly due to the significant increase of short-circuit current density (J(SC)) from 5.97 to 7.11-7.65 mA cm(-2). From the detailed morphological and photophysical studies, we have demonstrated that the employed unconventional materials of AIL are effective in exciton (of SubPc) blocking, thereby enhancing exciton diffusion towards the charge-separating interface of SubPc/C-60 and hence J(SC). Since these AIL materials all have a LUMO energy level very close to that of SubPc, the study reported here clarifies that the electron blocking is not a necessary property of an AIL material.