Figure 1

(a) THz electric field $\left[T\left(t\right)\right]$ transmitted through an unexcited Pc film (solid line) and the change in THz electric field $[-\Delta T\left(t\right)]$ under optical excitation at the optical-pump–THz-probe delay time $\Delta t=0$. The inset shows the spectrum of the transmitted THz pulse. (b) Frequency dependence of the real and imaginary parts of the photoconductivity $\left(\sigma \right)$ derived from the Pc film data in (a). The dashed lines are guides to the eye for a flat, frequency-independent response. (c) Relative change in the peak of THz transmission $-\Delta T∕T_0$ due to transient photoconductivity under optical excitation with $\lambda =580\mathrm{nm}$ and $F\sim 1\mathrm{mJ}∕{\mathrm{cm}}^2$, obtained in FPc crystals and FPc and Pc thin films as a function of optical-pump–THz-probe delay time $\Delta t$. Single-exponential fits to the thin-film data are also shown. The offset along the $y$ axis is for clarity. The inset illustrates the 0.4 ps onset of photoconductivity in these systems, limited by the time resolution of the setup.Reuse & Permissions

Figure 2

(a) Normalized intensity spectra of selected optical pump pulses. Spectra of pulses centered at 550 and 590 nm are not included for clarity. (b) Absorption spectra of a FPc crystal and FPc and Pc thin-film samples. (c) Product of mobility and photogeneration efficiency $\left(\mu \eta \right)$ measured in a FPc crystal and FPc and Pc thin-film samples at room temperature.Reuse & Permissions

Figure 3

Differential transmission of the peak of the THz probe pulse as a function of delay time and temperature. (a) FPc crystal under optical excitation at 400 nm with $F\sim 0.4\mathrm{mJ}∕{\mathrm{cm}}^2$ at temperatures of 298, 40, and 10 K. The inset shows a power-law fit $\Delta t^{-\beta }(\beta =0.55)$ to the data obtained at 80 K for $\Delta t>2\mathrm{ps}$. (b) Pc thin film under optical excitation at 580 nm with $F\sim 1\mathrm{mJ}∕{\mathrm{cm}}^2$ at temperatures of 298, 120, 80, and 20 K. Single-exponential fits to the data are also shown.Reuse & Permissions

Figure 4

Temperature dependence of the product of charge carrier mobility $\mu$ and photogeneration efficiency $\eta$ for several FPc crystal samples (solid symbols: squares and diamonds, samples 1 and 2 at 800-nm excitation; triangles and circles, samples 3 and 4 at 400-nm excitation), Pc thin films (open symbols: circles, sample 1 at 580-nm excitation; squares, sample 2 at 400-nm excitation), and a FPc thin film (open triangles at 580-nm excitation). A power-law fit $\mu \eta \sim {\left(T^o\right)}^{-n}(n=0.32)$ to the data obtained in the Pc thin film (sample 1) at 580-nm excitation is also shown. The inset shows the same data obtained in FPc crystals replotted on a semilogarithmic scale, where the solid line is a guide for the eye.Reuse & Permissions