title: Use of ultrafast time-resolved spectroscopy to demonstrate the effect of annealing on the performance of P3HT:PCBM solar cells.
abstract: The organic solar cells of heterojunction system, ITO/PEDOT:PSS/P3HT:PCBM/Al, with a thermal annealing after deposition of Al exhibit better performance than those with an annealing process before deposition of Al. In this study, ultrafast time-resolved spectroscopy is employed to reveal the underlying mechanism of annealing effects on the performance of P3HT:PCBM solar cell devices. The analyses of all decomposed relaxation processes show that the postannealed devices exhibit an increase in charge transfer, in the number of separated polarons and a reduction in the amount of recombination between excited carriers. Moreover, the longer lifetime for the excited carriers in postannealed devices indicates it is more likely to be dissociated into photocarriers and result in a larger value for photocurrent, which demonstrates the physical mechanism for increased device performance.
authors.affiliation: Department of Electrophysics, National Chiao Tung University , Hsinchu 30010, Taiwan.
authors.forename: Yu-Ting
authors.initials: YT
authors.lastname: Wang
authors.forename: Mei-Hsin
authors.initials: MH
authors.lastname: Chen
authors.forename: Chao-Ting
authors.initials: CT
authors.lastname: Lin
authors.forename: Jian-Jhih
authors.initials: JJ
authors.lastname: Fang
authors.forename: Che-Jui
authors.initials: CJ
authors.lastname: Chang
authors.forename: Chih-Wei
authors.initials: CW
authors.lastname: Luo
authors.forename: Atsushi
authors.initials: A
authors.lastname: Yabushita
authors.forename: Kaung-Hsiung
authors.initials: KH
authors.lastname: Wu
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Kobayashi
keywords: annealing effect; organic solar cells; ultrafast dynamics