Morphology-Dependent Carrier and Exciton Generations in Regioregular Poly(3-hexylthiophene) Polymer Diodes as Revealed by Bleaching Spectroscopy

Bleaching probe spectroscopy performed for regioregular poly(3-hexylthiophene) diodes reveals that coexistent morphological phases determine the conducting and optical properties of conjugated polymer films. Photoinduced absorption measurements demonstrate that exciton migration occurs from lamella aggregates to morphological sites consisting of quasiuncoupled chains and that the latter sites determine steady-state photophysical properties. Spectroscopy synchronized with diode operation reveals that the morphological locations of injected carriers in polymer diodes vary with the applied bias.

Figure 1

Steady-state absorption and cw photoinduced absorption (PIA) spectra of the RR-P3HT film. The horizontal broken line is the baseline for the PIA spectrum.

Figure 2

Transient PIA spectra of the RR-P3HT film recorded at 0, 10, 200, and 400 ps. The horizontal broken lines are the baselines for each spectrum and the vertical dotted line indicates the energy position of the 0-0 peak in the cw-PIA spectrum.

Figure 3

(a) DM spectra under $V_{\mathrm{dc}}+V_{\mathrm{ac}}=0\pm 1$, $0.7\pm 1$, and $1\pm 1\mathrm{V}$ and (b) the current-voltage characteristics for the RR-P3HT diode. (c) Schematic of hole injection by tunneling from PEDOT to two neutral states with different energy levels in P3HT. The two solid lines with different slopes in P3HT represent the difference of applied bias necessary for charge injection.

Figure 4

Bleaching spectra obtained from the cw-PIA measurements for RR-P3HT and RR-P3DDT films. The horizontal broken lines in the spectra are the baselines for each spectrum. The red solid curve for the spectra of RR-P3HT is a result of spectral simulation by the Franck-Condon model.