Experimental determination of the charge/neutral branching ratioηin the photoexcitation ofπ-conjugated polymers by broadband ultrafast spectroscopy

• DOI: 10.1103/physrevb.75.085206
• Publication Date: 2007-02-12T23:15:07Z
• Authors: C.-X. Sheng; M. Tong; S. Singh; Z. V. Vardeny
• Keywords: Branching (polymer chemistry)

We demonstrate a long-sought reliable method for determining the important branching ratio $\ensuremath{\eta}$ between photogenerated charged polarons and neutral excitons in $\ensuremath{\pi}$-conjugated polymer films solutions, using femtosecond transient photomodulation spectroscopy with broad spectral range from 0.14 to $2.7\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. found that both are instantaneously photogenerated, but critically depends on film nanomorphology, which ultimately controls interchain coupling strength. also correlation exists within each family obtained value, photoluminescence quantum efficiency, polarization memory lifetime; where strength determines them all. show varies less than 1% solutions glassy of poly(p-phenylene-vinylene) derivatives, chains relatively isolated; more 30% ordered contain lamellae, such as regio-regular poly(3-hexyl-thiophene). Our results may serve matching polymers specific device applications, large values good candidates photodetector photovoltaic whereas those small suitable active layers organic light emitting devices.