Capacitive currents, hysteresis and phase transitions in lead halide perovskite solar cells.

Germà Garcia-Belmonte^a

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Invited Speaker, Germà Garcia-Belmonte, presentation 085
Publication date: 5th February 2015

Hybrid lead halide perovskite-based solar cells have rapidly reached very large solar to electricity power conversion efficiencies. The most extensively studied has been the CH3NH3PbI3 perovskite (or its analogous but using chlorine precursor: CH3NH3PbI3-xClx) as absorber materials, in combination with electron (TiO2) and hole (spiro-OMeTad) selective contacts. An intriguing effect manifested as a hysteretic response of the current-voltage curve upon illumination has been extensively reported. Hysteresis has a detrimental influence on the photovoltaic operation reliability and stability so as to advance in its alleviation. Upon illumination perovskite-based solar cells exhibit a giant capacitance observable in the low frequency response.¹ Even in dark conditions an extra capacitance appears in excess of geometrical or chemical capacitance operating at intermediate- or high-frequency parts of the capacitance spectra. A connection between the low-frequency capacitance and the hysteretic effect of the current-voltage curves upon illumination has been also suggested,² although an experimental correlation is still lacking. We propose here a method to isolate capacitive currents from current-voltage curves and explain how low-frequency capacitance values are connected to the hysteretic response. Capacitive kinetic effects on the solar cell response are analyzed as a function of temperature. It is observed that variations in capacitance spectra are related to perovskite phase transitions, particularly for the orthorhombic to tetragonal structure change. It is then inferred that the hysteretic response, which exhibits a slow kinetics at room temperature, has a capacitive origin. Mechanisms behind the capacitive effect are further discussed.

1. Juarez-Perez, E. J.; Sanchez, R. S.; Badia, L.; Garcia-Belmonte, G.; Kang, Y. S.; Mora-Sero, I.; Bisquert, J. Photoinduced Giant Dielectric Constant in Lead Halide Perovskite Solar Cells. Journal of Physical Chemistry Letters 2014,5, 2390-2394. 2. Sanchez, R. S.; Gonzalez-Pedro, V.; Lee, J.-W.; Park, N.-G.; Kang, Y. S.; Mora-Sero, I.; Bisquert, J. Slow Dynamic Processes in Lead Halide Perovskite Solar Cells. Characteristic Times and Hysteresis. Journal of Physical Chemistry Letters 2014,5, 2357-2363.

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