The transient photocurrent measurements were performed at 10% white light as the baseline with a green light pulse (λ=530 nm). For the white light source, an array of nine white light diodes was used (SP-12-W5, cool white Luxeon Rebel) controlled by a Keithley power source (PSW4323). An additional Keithley power source controlled the green light source. A fast solid-state switch was used to ensure a fast rise and decay of the colored LEDs (a squared pulse with 100 ns rise and fall time). The intensity of the green pulse was 5 % of a sun (i.e., 50 % of the steady state white light).