Journal Article Temperature effects on carrier formation dynamics in organic heterojunction solar cell

Yonezawa, Kouhei  ,  Yasuda, Takeshi  ,  Moritomo, Yutaka

107 ( 13 )  , p.133903 , 2015-09 , American Institute of Physics
The femto-second time-resolved spectroscopy was performed on the heterojunction (HJ) solar cell which consists of prototypical low-band gap donor (D), poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5- b' ] dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b] thiophenediyl]] (PTB7), and the C70 acceptor (A). We spectroscopically determined the absolute number of donor exciton ( nD* ), acceptor exciton ( nA* ), and carrier ( nD+ ) per an absorbed photon against the delay time (t). At 300 K, we found that the decay time ( τdecay  = 3.5 ps) of A* is much longer than the carrier formation time ( τform  = 1.1 ps), indicating that the late A* component does not contribute to the carrier formation process. The elongated τform (=1.5 ps) at 80 K is ascribed to the exciton migration process, not to the exciton dissociation process.

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