科研之友
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摘要
We measured the picoseconds (ps) transient photomodulation (PM) dynamics of photoexcitations in blends of regio-regular poly(3-hexyl-thiophene) [RR-P3HT] (donors-D) and indene-C-60 bisadduct (fullerene derivative) [ICBA] (acceptor-A) that phase-separate into D- and A-nano-domains, in a broad spectral range from 0.25 to 2.5 eV; in comparison with steady state PM spectra. We correlate our measurements with organic photovoltaic solar cell performance made from the same D and A materials. In D-A blends of RR-P3HT/ICBA with (1.2:1) weight ratio having solar cell power conversion efficiency of similar to 5.1%, we found that although the intrachain excitons in the polymer nano-domains decay within similar to 10 ps, no charge polarons are generated on their expense up to similar to 1 ns. Instead, there is a built-up of charge-transfer (CT) excitons at the D-A domain interfaces that occurs with the same kinetics as the exciton decay. The CT excitons dissociate into separate polarons in the D-and A-nano-domains at a much later time (>> 1 ns). This "two-step" charge photogeneration process is typical in organic bulk heterojunction cells. Our results emphasize the important role of the CT state in generating free charge polarons in organic solar cells.
- 出版日期2012-12-15
