Kevin Ho1,Rajiv Giridharagopal1,Yangwei Shi1,Yujing Lin1,David Ginger1
University of Washington1
Kevin Ho1,Rajiv Giridharagopal1,Yangwei Shi1,Yujing Lin1,David Ginger1
University of Washington1
Halide perovskites are known to be tolerant to defects while exhibiting long carrier lifetimes. At the same time, it is known that lifetimes are spatially-dependent, with grains and grain boundaries exhibiting different levels of nonradiative recombination and therefore different carrier dynamics. In order to approach the radiative efficiency limits in these devices, it is essential to understand the variation of carrier trapping and de-trapping dynamics between grains and grain boundaries and to improve the carrier dynamics at these locations. Here, we use intensity modulated scanning Kelvin probe microscopy (IM-SKPM) to directly image carrier dynamics at the tens of nanosecond timescale, with high spatial resolution on the order of ~80-100 nanometers. We apply IM-SKPM to study the perovskite FA<sub>0.83</sub>Cs<sub>0.17</sub>Pb(Br<sub>x</sub>I<sub>1-x</sub>)<sub>3</sub> with varying halide composition. We observe lower carrier lifetimes from IM-SKPM at the grain boundaries, suggesting that the boundaries are not benign and result in higher carrier trapping. Furthermore, we use IM-SKPM to study how surface passivating agents affect the distribution of carrier lifetimes. The perovskites were passivated with (3-aminopropyl)triethoxysilane (APTMS) which allowed us to investigate the effect of passivation on the local variation of charge carrier dynamics. After passivation, we found that the IM-SKPM lifetimes increased due to a reduction of trap densities. However, a variation in the carrier lifetimes was still observed corresponding to the non-uniformity of the passivator. Importantly, these results show that IM-SKPM can be correlated with the photoluminescence lifetime trends, but at nanoscale spatial resolution far below the optical diffraction limit.