Temperature-independent carrier formation dynamics in bulk heterojunction

Abstract

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′′-nhexy-[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 (nD) and acceptor (nA∗) excitons per absorbed photon as functions of the delay time (t), in addition to the relative number of donor carries (nDt). We found that the carrier formation dynamics is independent of temperature at 300 and 80 K: the carrier formation time (rise = 0.4 ps) is much faster than the decay time (decay? 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.