Figure 1. TDCF traces at short delay to probe the field dependence of rapid non-geminate recombination.

(a) The external generation efficiency of a 70 nm thick PCDTBT:PCBM blend device, measured with TDCF as a function of pre-bias for 3.5 and 12 ns delay time and fluences of 0.005, 0.05, 0.1 and 0.4 μJ/cm². Pulsed illumination was at an excitation wavelength of 532 nm with a laser pulse length of 0.6 ns or 6 ns for 3.5 ns and 12 ns delay, respectively. For comparison, the JV-curve of the same device under simulated AM 1.5 G light calibrated to 100 mW/cm² is shown by a solid line. The scaling of the two y-axes was chosen to overlay the low fluence EGE at a reverse bias of −2 V with the current density at the same bias. (b) The total collected charge density as a function of laser fluence measured with a pre-bias V_pre of 0.7 V and a collection bias V_coll of −3 V.