Photophysics of Semiconducting Polymers

Undoped conjugated polymers have an anisotropic, quasi-one-dimensional electronic structure with the tt electrons coupled to the polymer backbone via electron-phonon interactions. The overlapping of TT- (also TT -) electron wave functions forms a valence band (conduction band) with a gap size of typically 2-4 eV, corresponding to the conventional semiconductor gap. As a result, undoped conjugated polymers (hereafter called simply semiconducting polymers) exhibit the electronic and optical properties of semiconductors in combination with the mechanical properties of general polymers, making them potentially useful for a wide array of applications. 

Steady-State and Near-Stetufy-State Photoexcitation Spectroscopy 

Spectroscopy studies of conjugated polymers have been an important source of information on their electronic structure in particular, photoinduced absorption (excitation spectroscopy) has successfully characterized the gap states associated with the nonlinear excitations (solitons, polarons, and bipolarons) and determined the energies of those states relative to the conduction and valence bands in several conjugated polymers. 

In sub-picosecond photoexdtation spectroscopy (or time-resolved excited spectroscopy) of the conjugated polymers, one can study the excited-state spectra (absorption, emission, and stimulated emission) and the time decay of the excited-state spectral features. For nonlinear excitations in conjugated polymers, this spectroscopy technique is useful, since their photogeneration processes usually occur in the sub-nanosecond time domain. 

Time-resolved photoluminescence spectroscopy has emerged as one of the most important tools for studying the properties of solid-state materials suited to optoelectronic applications, including semiconducting polymers. This is due to the relatively direct information about the excitation dynamics, such as recombination and relaxation processes, which is obtained from such experiments. Wong et al. [1232] have reported a luminescence lifetime much smaller than 1 ns in conjugated polymers and have pointed out that nonradiative as well as bimolecular processes might play an important role. Furukawa et al. [1233] have studied time-resolved luminescence in PPV and have explained the re- 

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Sariciftci, N.S., and A.J. Heeger. 1995. Photophysics of semiconducting polymer C60 composites— A comparative study. Synth Met 70 1349-1352. 

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