Journal Article Temperature-independent carrier formation dynamics in bulk heterojunction

Yonezawa, Kouhei  ,  Yasuda, Takeshi  ,  Moritomo, Yutaka

8 ( 11 )  , p.112301 , 2015-10 , The Japan Society of Applied Physics
We investigated the effects of temperature on the carrier formation dynamics in a small-molecular blend film, 2,5-di-(2-ethylhexyl)-3,6-bis-(5''-n-hexy-[2,2',5',2'']terthiophen-5-yl)-pyrrolo[3,4-c]pyrrolo-1,4-dione (SMDPPEH)/[6,6]-phenyl C71-butyric acid methyl ester (PC71BM). We spectroscopically determined the absolute numbers of donor ($n_{\text{D}^{*}}$) and acceptor ($n_{\text{A}^{*}}$) excitons per absorbed photon as functions of the delay time (t), in addition to the relative number of donor carries ($n_{\text{D}^{+}}$). We found that the carrier formation dynamics is independent of temperature at 300 and 80 K: the carrier formation time (τrise = 0.4 ps) is much faster than the decay time (τdecay ≈ 2.5 ps) of donor excitons. The temperature independence strongly suggests that only excitons created near the donor–acceptor interface contribute to the carrier formation.

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