Browsing by Author "Liu, Chiou-Hua"

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Dark carrier recombination in organic solar cell
(2008-09-29)
Wang, Ying-Xuan
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Tseng, Shin-Rong
;
Meng, Hsin-Fei
;
Lee, Kuan-Chen
;
Liu, Chiou-Hua
The carrier recombination in organic solar cells is investigated by numerical modeling to understand the weak dependence of theopen-circuit voltage on the workfunction of the electrodes. In Ohmic contact structures, photocarriers recombine predominantly with dark carriers diffused from the electrode into the semiconductor. Such dark carrier recombination becomes the main limit of power conversion efficiency and open-circuit voltage. For a given semiconductor decreasing the workfunction difference of the electrodes reduces simultaneously the dark carrier recombination and the flat band voltage. The balance between these two opposite factors gives a nearly constant open-circuit voltage. In an ideal bilayer structure there is no dark carrier recombination and the efficiency is demonstrated to be 60% higher than single layer blend. (C) 2008 American Institute of Physics.
The effect of carrier mobility in organic solar cells
(2010-04-15)
Shieh, Ji-Ting
;
Liu, Chiou-Hua
;
Meng, Hsin-Fei
;
Tseng, Shin-Rong
;
Chao, Yu-Chiang
The microscopic states and performance of organic solar cell are investigated theoretically to explore the effect of the carrier mobility. With Ohmic contacts between the semiconductor and the metal electrodes there are two origins of carriers in the semiconductor: the photocarriers generated by photon absorption and the dark carriers diffused from the electrodes. The power efficiency of the solar cell is limited by the recombination of a carrier with either the photocarrier or a dark carrier. Near the short-circuit condition the photocarrier recombination in the semiconductor bulk decreases as the mobility increases. Near the open-circuit condition the dark carrier recombination increases with the mobility. These two opposite effects balance with one another, resulting in an optimal mobility about 10(-2) cm(2)/V s which gives the highest power conversion efficiency. The balance of the electron and hole mobilities are not necessary to maintain the optimal efficiency also because of the balance of the photocarrier and dark carrier recombination. The efficiency remains about the same as one carrier mobility is fixed at 10(-2) cm(2)/V s while the other one varies from 10(-1) to 10(-3) cm(2)/V s. For solar cell with a Schottky barrier between the semiconductor and the metal electrode there is no dark carrier recombination. The efficiency therefore always increases with the mobility. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3327210]