Microsecond Bias Polarity Switching Reveals Hidden Charge Dynamics at Halide Perovskite Interfaces

Abstract

We present a time-domain technique based on rapid bias polarity switching (BiPS) to probe charge transport and near-surface defects in halide perovskite single crystals. The method exploits interfacial extraction barriers, which cause carrier accumulation and subsequent release after bias reversal. BiPS combines surface sensitivity (200 nm-2 $\hat{I}¼$m) with millimeter-scale reach, enabling reconstruction of internal field profiles, detection of bulk space charge down to $10^9$ cm${}^{-3}$, and resolution of microsecond-millisecond trap dynamics. In our setup the surface-state detection limit is $10^9$ cm${}^{-2}$, and could be further improved by optimized illumination and readout. Applied to melt-grown CsPbBr${}_3$ (Cr/Cr) and solution-grown MAPbBr${}_3$ (Cr/SnO${}_2$/Cr), BiPS reveals interfacial barriers that drive hole accumulation and defect filling. CsPbBr${}_3$ shows long-lived space charge ($\sim 3\times 10^{11}$ cm${}^{-3}$) and $\sim 250\times$ faster hole extraction than MAPbBr${}_3$, while trap analysis yields capture times of 1-100 $\hat{I}¼$s, detrapping times of 20 $\hat{I}¼$s-3 ms, and activation energies of 300-500 meV. BiPS thus provides direct access to buried interfacial processes, disentangles electronic and ionic contributions, and offers a robust platform for evaluating contacts and guiding defect engineering in perovskite optoelectronic devices.

25 pages, 8 figures in main article; SI 13 pages, 10 figures