Vibrational sum-frequency generation spectroscopy (SFG) was used for in situ studies of the electrified interface of the negative electrode (anode) of a lithium battery analog. In a lithium battery, lithium is deposited interstitially in a carbon anode. In the model system, which facilitates the study of the solid-electrolyte interphase (SEI) the anode was Au and lithium was deposited on the anode surface. The electrolyte was LiClO4 plus ethylene carbonate (EC) and diluted with tetrahydrofuran (THF). The SEI created on the anode in this case consists primarily of lithium ethylene dicarbonate (LiEDC) and lithium salts. SFG experiments were run during multiple cycles of reduction and oxidation of a half-cell, corresponding to charging and discharging of a battery. The infrared (IR) pulses were tuned to EC carbonyl transitions or −CH2 transitions of LiEDC and THF. A model is introduced to describe potential-dependent SFG intensities at electrified interfaces when the electrolyte has intense IR transitions. The electrified interface is defined as consisting of the electrode–electrolyte (or electrode–SEI) interface, plus bulk material located within a Debye length of the electrode. We show that SFG can detect and characterize the underpotential deposition and stripping of lithium on the Au anode, and we observe the growth and structural evolution of the SEI at the anode. During the first three charge/discharge cycles, SEI growth is hindered by the presence of THF, but after the third cycle the THF has been expelled and SEI growth accelerates and then levels off.

Halide perovskites have undergone remarkable developments as highly efficient optoelectronic materials for a variety of applications. Several studies indicated the critical role of defects on the performance of perovskite devices. However, the parameters of defects and their interplay with free charge carriers remain unclear. In this study, we explored the dynamics of free holes in methylammonium lead tribromide (MAPbBr3) single crystals using the time-of-flight (ToF) current spectroscopy. By combining ToF spectroscopy and Monte Carlo simulation, three energy states were detected in the bandgap of MAPbBr3. In addition, we found the trapping and detrapping rates of free holes ranging from a few microseconds to hundreds of microseconds. Contrary to previous studies, we revealed a strong detrapping activity of traps. We showed that these traps substantially affect the transport properties of MAPbBr3, including mobility and mobility-lifetime product. Our results provide an insight on charge transport properties of perovskite semiconductors.

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