TY - JOUR
T1 - Impedance Spectroscopic Indication for Solid State Electrochemical Reaction in (CH3NH3)PbI3 Films
AU - Zohar, Arava
AU - Kedem, Nir
AU - Levine, Igal
AU - Zohar, Dorin
AU - Vilan, Ayelet
AU - Ehre, David
AU - Hodes, Gary
AU - Cahen, David
N1 - Publisher Copyright:
© 2015 American Chemical Society.
PY - 2016/1/7
Y1 - 2016/1/7
N2 - 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.
AB - 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.
KW - contact potential difference
KW - halide perovskite solar cells
KW - impedance spectroscopy
KW - surface photovoltage
UR - http://www.scopus.com/inward/record.url?scp=84953873513&partnerID=8YFLogxK
U2 - 10.1021/acs.jpclett.5b02618
DO - 10.1021/acs.jpclett.5b02618
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AN - SCOPUS:84953873513
SN - 1948-7185
VL - 7
SP - 191
EP - 197
JO - Journal of Physical Chemistry Letters
JF - Journal of Physical Chemistry Letters
IS - 1
ER -