Figure 6
Temporal response of C60 nanorod photoconductors.
(a) The transient photocurrent response of a typical photodoped C60 nanorod photoconductor device measured under ~514 nm illumination (~312 µWcm−2) modulated at 13 Hz with an applied electric field of 10 Vµm−1. The device exhibits a rise time of 7.5 ms. (b) The photocurrent response of the same device under the identical measurement conditions except for an increase in the modulation frequency to 50 kHz. (c) Spectral responsivity of the photoconductor device as a function of modulation frequency measured at an applied electric field of 3 Vµm−1. The photoconductor shows a typical decrease in the responsivity with increase in frequency. The features at ~50 Hz and ~100 Hz correspond to notch filters applied by the lock-in amplifier to remove line-frequency artefacts. The device displays the ability to measure ac signals up to ~250 kHz (the limit of the lock-in amplifier). Inset to (c) is the current-voltage characteristic of the device under dark and light conditions. (d) The transient response of photoconductor device measured under 510 nm pulsed (~8 ns at a 21 Hz repetition rate) illumination. The device displays a fast rise time of 60 µs (inset) and a slow decay indicating the presence of long lived trap states in the optically active material composite. The solid red line represents a fit consisting of the sum of three exponential decays.
