Figure 9

Measurement of the photocurrent responses of CdS (a) and CdS/WO_x (b) at 0 V versus Ag/AgCl (3.0 M) in a three-electrode configuration with a platinum mesh counter electrode and aqueous Na₂SO₄ (0.5 M) electrolyte, with more detailed fitting of the response (c) and relaxation (d) curves of CdS/WO_x shown respectively as functions of the time since turn-on, t_on, and the time since turn-off, t_off, of the illumination; backside-illumination was provided by a white LED source at a power density of 99.3 mW cm⁻². In the case of the CdS/WO_x electrode, the decay of the photocurrent during prolonged illumination (b) is modelled by a mono-exponential fitting function described by Eq. 1 in the limit of large t_on (the fit has been applied over t_on values greater than 2,000 s), while the photocurrent response (c) and relaxation (d) curves of this sample are fitted according to the full bi-exponential relationships given by Eqs 1, 2, respectively; all fitting curves are plotted as solid red lines, and the annotations “On” and “Off” indicate the switching times of the LED source.