Silver Iodide Formation in Methyl Ammonium Lead Iodide Perovskite Solar Cells with Silver Top Electrodes

• Published in: Advanced materials interfaces Vol. 2; no. 13; pp. np - n/a
• Main Authors: Kato, Yuichi, Ono, Luis K., Lee, Michael V., Wang, Shenghao, Raga, Sonia R., Qi, Yabing
• Format: Journal Article
• Language: English
• Published: Weinheim John Wiley & Sons, Inc 01.09.2015
• Subjects: Colors (materials); Electrodes; Iodides; Iodine; perovskite solar cells; Perovskites; Photovoltaic cells; Silver; Silver iodides; Solar cells; X‐ray diffraction; X‐ray photoelectron spectroscopy
• ISSN: 2196-7350; 2196-7350
• DOI: 10.1002/admi.201500195

Silver is a low‐cost candidate electrode material for perovskite solar cells. However, in such cells the silver electrodes turn yellow within days of device fabrication. The color change is also accompanied by a dramatic decrease in the power conversion efficiency when compared to otherwise identical devices using gold electrodes. Here, it is shown that the color change results from silver oxidation to silver iodide, due to a reaction with iodine in methyl ammonium lead perovskite. The change in X‐ray diffraction and X‐ray photo­electron spectroscopy is discussed. Exposure to air accelerates corrosion of the Ag electrodes when compared to dry nitrogen gas exposure. However, iodine not reacted with silver is observed by X‐ray photoelectron spectroscopy even for the perovskite solar cell kept in dry nitrogen gas. It is proposed that silver iodide is formed when methyl ammonium iodide migration is facilitated by the small pinholes in the hole transport layer spiro‐MeOTAD. Silver is a low‐cost candidate electrode material for perovskite solar cells. However, the color of silver changes because of silver oxidation to silver iodide due to a reaction with iodine in methyl ammonium lead perovskite. It is suspected that silver iodide is formed when methyl ammonium iodide migrates through the small pinholes in the hole transport layer spiro‐MeOTAD.