Browsing by Author "Liu, I-Hsiu"

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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
;
Kuo, Ya-Ching
;
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.
Origins of vertical phase separation in P3HT:PCBM mixed films
(2014-04-01)
Liu, I-Hsiu
;
Chao, Yi-Ping
;
Fang, Jian-Jhih
;
Tseng, Wei-Hsuan
;
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