Photoinduced absorption in an alternating polyfluorene copolymer for photovoltaic applications

The authors present a detailed study of a novel alternating polyfluorene copolymer, poly[2,7-(9,9-dioctyl-fluorene)-alt-5,5-(4\u27,7\u27-di-2-thienyl-2\u27,1\u27,3-benzo-thiadiazole)], and its blends with the fullerene deriv. [6,6]-phenyl-C61-butyric acid Me ester, using continuous wave photoinduced absorption (PA) techniques. The authors also present the use of phase information from the PA measurements for estg. the no. of different photoexcitation types present in the PA spectra as well as their lifetimes. In all blends the PA spectra show a broad high-energy PA band ranging from .apprx.1 to 2 eV as well as a low-energy band at .apprx.0.35 eV. The authors find two kinds of excitations present at 80 DegK, polarons showing dispersive recombination with lifetimes of roughly a millisecond, and a 2nd kind of photoexcitation tentatively assigned to coulombically bound intrachain polaron pairs showing practically nondispersive recombination with a lifetime of .apprx.20 ms. [on SciFinder (R)

Recombination studies in a polyfluorene copolymer for photovoltaic applications

We present detailed continuous wave (cw) and transient photoinduced absorption (PA) measurements in thin films of a novel alternating polyfluorene copolymer, poly[2,7-(9,9-dioctyl-fluorene)-alt-5,5-(4',7'-di-2-thienyl-2',1',3-benzo-thiadiazole)] (DiO-PFDTBT), and its blends with the sol. fullerene deriv. [6,6]-phenyl-C61-butyric acid Me ester (PCBM) in wt. ratios of 1:0, 4:1 and 1:4. We measure the frequency, intensity and temp. dependence of the PA signal in the frequency domain, and compare with the results obtained from the transient PA decay measurements in the time domain. In all blends, the PA spectrum shows a broad high energy PA band ranging from .apprx.1 eV to 2 eV as well as a low energy band peaking at .apprx.0.35 eV. We attribute the low energy band to the P1 transition of polarons and part of the high energy band to the correlated P2 transition of polarons. Both frequency and time domain measurements show that the high energy band has two decay components, a faster component in the microsecond time regime and a slower component in the millisecond time regime. The slow component is strongly dispersive, whereas the fast component is practically non-dispersive. [on SciFinder (R)