Beyond the admirable photovoltaic properties, the unique opto-electrical properties of organic-inorganic halide perovskite (OIHP) combined with their relatively low-cost production, have made this class of materials a great candidate in photodetectors¹, LEDs², and radiation sensors³. Key to optimization of these applications is the understanding of the fundamental physical and chemical processes at the electrode interface^{4, 5, 6}. Charge injection at electrode-OIHPs interface may induce interfacial trapped states and recombination regions leading to unfavorable effect on charge collection efficiency,^{7, 8} induce electrochemical reactions and result in interfacial degradation^{4, 8}. The latter can be pure- metal-OIHP process, or additionally mediated by the presence of environment at the triple-phase boundaries.^{5, 9}

The lack of understanding stems largely from the lack of appropriate tools to capture the electrochemical dynamics on the length scales of the local inhomogeneities and time scales over which the coupled dynamics take place. Here, we implemented Kelvin probe force microscopy (KPFM) for probing charge dynamics at electrode-OIHPs interface on time scales from minutes to seconds (KPFM), milliseconds (time resolved (tr-) KPFM) and microseconds (G-KPFM) to explore the spatial and temporal charge dynamics at MAPbBr₃ devices as a model system. KPFM provides a nanoscale profile of device potential as a function of time during application of an external stimuli (light and bias). This allows us to gain insight into the temporal dynamics at the electrode- OIHPs interface activated by electric field. Indeed, the multimodal KPFM is a complementary measurement to the impedance spectroscopy as the impedance provides information on the relaxation process in frequency domain while KPFM provide information on the local relaxation phenomena in time domain. 

Unlike electronic processes, the ionic and electrochemical phenomena can be semi- or non-reversible and highly non-linear. Although evidence of ion migration by KPFM has been reported previously^{10, 11}, standard KPFM is not well-suited to explore time dependent phenomena due to the limited time resolution (~1 sec) of the approach. Therefore, we employ time resolved (tr-) and ultrafast (G-mode) KPFM to directly probe the dynamic spatio-temporal behavior of the in-operandi device. G-KPFM has previously been shown to provide ~10s µs time resolution with 10s nm spatial resolution, making it a suitable approach for detecting and separating field induced fast transport processes^{12, 13}.

            The nature of the electrochemical phenomena at the metal-OHIP interfaces is explored via the in-situ time of flight secondary ion mass spectrometry (ToF – SIMS) measurements. We explore the changes of the ionic concentrations along the surface of the laterally electrode structure under applied bias, identifying the nature of the mobile ionic carriers and their bias responses. The changes in the responses in the presence of illumination are further elucidated.

            The results demonstrate an interplay of several phenomena, including charge injection, recombination and ion migration, leading to an unbalanced charge dynamic in MAPbBr₃-Au interface under forward and reverse biases, explaining the origin of the current-voltage hysteresis in these devices. We contrast the bias assisted charge dynamics under both illuminated and dark conditions. Our multimodal time scale KPFM measurements reveal that the charge transport behavior in hybrid perovskites are light, bias and environmental dependent providing a comprehensive picture of overall carrier dynamics and interface properties in MAPbBr₃ perovskites with lateral Au electrodes.