Non-ferroelectric nature of the conductance hysteresis in CH3NH3PbI3 perovskite-based photovoltaic devices

TL;DR

This study investigates conductance hysteresis in CH3NH3PbI3 perovskite films, demonstrating that ionic migration, not ferroelectricity, causes the hysteresis, which impacts device efficiency.

Contribution

It provides evidence that ionic migration, rather than ferroelectricity, explains conductance hysteresis in perovskite solar cells, challenging previous assumptions.

Findings

Hysteresis strongly depends on frequency, inconsistent with ferroelectric behavior.

Ionic migration explains the observed hysteresis and impedance features.

Intrinsic polarization is limited to about 1 μC/cm2, ruling out ferroelectricity.

Abstract

We present measurements of conductance hysteresis on CH3NH3PbI3 perovskite thin films, performed using the double-wave method, in order to investigate the possibility of a ferroelectric response. A strong frequency dependence of the hysteresis is observed in the range of 0.1 Hz to 150 Hz, with a hysteretic charge density in excess of 1000 {\mu}C/cm2 at frequencies below 0.4 Hz - a behaviour uncharacteristic of a ferroelectric response. We show that the observed hysteretic conductance, as well as the presence of a double arc in the impedance spectroscopy, can be fully explained by the migration of mobile ions under bias on a timescale of seconds. Our measurements place an upper limit of approximately 1 {\mu}C/cm2 on any intrinsic frequency-independent polarisation, ruling out ferroelectricity as the main cause of current-voltage hysteresis and providing further evidence of the importance of ionic migration in modifying the efficiency of CH3NH3PbI3 devices.