Charge Carrier Dynamics of Vapor-Deposited Small-Molecule/Fullerene Organic Solar Cells

摘要

Although small-molecule organic solar cells (SMOSCs) have shown increasingly promising prospects as a source of solar power, there have been few studies concerning the photophysics of these systems. Here, we report the time scale aad efficiency of charge separation and recombination in a vapor-deposited SMOSC material that produces 5.81% power conversion efficiency. Transient absorption and time-resolved photolumines-cence (trPL) studies of thin film blends comprising DTDCTB, a narrow-band gap electron donor, and either C_(60) or C_(70) as an electron acceptor show that charge separation occurs in ～100 fs, while charge recombination takes place over sub-ns and ns time scales. trPL indicates a donor electron-hole pair lifetime of ～33 ps in the neat film and reveals that ～20% of donors fail to charge separate in donor-acceptor mixed films, likely owing to some spatially extended donor-rich regions that interact poorly with acceptors. Our results suggest that morphological manipulations of this material could further improve device efficiency.