| 초록 |
The bulk heterojunction (BHJ) material comprised of conjugated polymer and the soluble fullerene derivative, PCBM, has exhibited high solar-to-electric power conversion efficiency in polymer-based solar cells. We have investigated the generation mechanism of mobile carriers and the carrier recombination/decay dynamics underlying the high performance of this system. We find that in polymer:fullerene composites mobile carriers are generated via a two step process: An initial ultrafast electron transfer to a charge transfer (CT) bound state, followed by the injection of mobile carriers into the bicontinuous network. We show that the carrier recombination is affected by the time spent in the CT state. Our ultrafast spectroscopic studies unravel the interplay between these processes (which determine the eventual photovoltaic device performance) and their dependence on the specific electronic structure in the crystalline and amorphous regions within the nano-structure of the composite. |
