Reactions at Noble Metal Contacts with Methylammonium Lead Triiodide Perovskites: Role of Underpotential Deposition and Electrochemistry
Journal Article - Open Access
Princeton University Princeton United States
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Chemical reactivity of halide perovskites coupled with a low energy of formation makes it a challenge to characterize material properties and achieve long-term device stability. In this study, we elucidate electrochemical reactions occurring at the methylammonium lead triiodide MAPbI3Au interface. X-ray photoemission spectroscopy is used to identify a type of reductionoxidation reaction termed underpotentialdeposition UPD involving lead, iodine, and hydrogen occurring at interfaces with noble metals. Changes in surface compositions andoxidation states suggest that UPD derived adsorbates at MAPbI3Au interfaces lower the energy barrier for release of volatile HI andor I2catalyzing degradation at exposed contacts. Additionally, comparison to PbI2Au interfaces demonstrates that the presence of methylammoniummethylamine accelerates the formation of a Pb0 adlayer on the Au. Reactions involving UPD Pb0 can transform the typically anodic hole collecting Au to a cathode in a photovoltaic measurement. Cyclic voltammetry reveals electrochemical reaction peaks in indium tin oxide ITOMAPbI3Au devices occurring within voltage ranges commonly used for perovskite characterization. The electrochemical stability window of this device architecture is measured to be between 0.5 V and 0.9 V. Voltage induced interfacial reactions contribute to reversible electrochemical peaks, hysteresis, switchable perovskite diode polarity, and permanent degradation at larger voltages. These types of surface reactions alter the interfaceinterphase composition beyond ion accumulation, provide a source for the diffusion of defects, and contribute to electrode material dependent current-voltage hysteresis. Moreover, the results imply fundamental limitations to achieving high device stability with noble metals andor methylammonium containing perovskites.
- Physical Chemistry
- Electrical and Electronic Equipment