Impedance Spectroscopic Indication for Solid State Electrochemical Reaction in (CH3NH3)PbI3 Films

详细信息    查看全文

• 作者：Arava Zohar ; Nir Kedem ; Igal Levine ; Dorin Zohar ; Ayelet Vilan ; David Ehre ; Gary Hodes ; David Cahen
• 刊名：The Journal of Physical Chemistry Letters
• 出版年：2016
• 出版时间：January 7, 2016
• 年：2016
• 卷：7
• 期：1
• 页码：191-197
• 全文大小：334K
• ISSN：1948-7185

文摘

Halide perovskite-based solar cells still have limited reproducibility, stability, and incomplete understanding of how they work. We track electronic processes in [CH₃NH₃]PbI₃(Cl) (“perovskite”) films in vacuo, and in N₂, air, and O₂, using impedance spectroscopy (IS), contact potential difference, and surface photovoltage measurements, providing direct evidence for perovskite sensitivity to the ambient environment. Two major characteristics of the perovskite IS response change with ambient environment, viz. -1- appearance of negative capacitance in vacuo or post-vacuo N₂ exposure, indicating for the first time an electrochemical process in the perovskite, and -2- orders of magnitude decrease in the film resistance upon transferring the film from O₂-rich ambient atmosphere to vacuum. The same change in ambient conditions also results in a 0.5 V decrease in the material work function. We suggest that facile adsorption of oxygen onto the film dedopes it from n-type toward intrinsic. These effects influence any material characterization, i.e., results may be ambient-dependent due to changes in the material’s electrical properties and electrochemical reactivity, which can also affect material stability.