In Situ Measurement Of Electric-Field Screening In Hysteresis-Free Ptaa/Fa(0.83)Cs(0.17)Pb(I0.83br0.17)(3)/C60 Perovskite Solar Cells Gives An Ion Mobility Of Similar To 3 X 10(-7) Cm(2)/(V S), 2 Orders Of Magnitude Faster Than Reported For Metal-Oxide-Contacted Perovskite Cells With Hysteresis

We apply a series of transient measurements to operational perovskite solar cells of the architecture ITO/PTAA/FA(0.83)Cs(0.17)Pb(I0.83Br0.17)(3)/C60/BCP/Ag, and similar cells with FA(0.83)MA(0.17). The cells show no detectable JV hysteresis. Using photocurrent transients at applied bias we find a similar to 1 ms time scale for the electric field screening by mobile ions in these cells. We confirm our interpretation of the transient measurements using a drift-diffusion model. Using Coulometry during field screening relaxation at short circuit, we determine the mobile ion concentration to be similar to 1 x 10(18)/cm(3). Using a model with one mobile ion species, the concentration and the screening time require an ion mobility of similar to 3 x 10(-7) cm(2)/(V s). As far as we know, this article gives the first direct measurement of the ion mobility and concentration in a fully functional perovskite solar cell. The measured ion mobility is 2 orders of magnitude higher than the highest estimates previously determined using perovskite solar cells and perovskite thin films, and 3 orders of magnitude higher than is frequently used in modeling hysteresis effects. We provide evidence that the fast field screening is due to mobile ions, as opposed to dark injection and trapping of electronic carriers.