Abstract
AbstractSeemingly contradictory reports on polar domains and their origin have surrounded the controversial discussion about the ferroelectricity of the methyl ammonium lead iodide (MAPbI3) thin films that are commonly employed in perovskite solar cells. In this work, microscopic modulations of the polar domain patterns upon application of an electric poling field are correlated with macroscopic changes to the currents through the MAPbI3 layer. Piezoresponse force microscopy is used to monitor the widening, narrowing, generation or extinction of polar domains, as well as shifts of the domain walls at room temperature under an in‐plane electric poling field that is applied between two laterally organized electrodes. This poling leads to a net polarization of individual grains and the thin film itself. Macroscopically, this net polarization results in a persistent shift of the diode characteristics that is measured across the channel between the electrodes. Both the modulation of the polar domains upon electric poling and the concurrent persistent shift of the electric currents through the device are the unambiguous hallmarks of ferroelectricity, which demonstrate that MAPbI3 is a ferroelectric semiconductor.
Highlights
Contradictory reports on polar domains and their origin have surlow non-radiative recombination losses and the hysteresis in current density–voltage rounded the controversial discussion about the ferroelectricity of the methyl (J–V) curves of solar cells.[1,2,3] To date, the ammonium lead iodide (MAPbI3) thin films that are commonly employed in perovskite solar cells
We used the two-step deposition process for the MAPbI3 layer and the subsequent solvent-vapor annealing that we described in our previous reports on polar domains in perovskite solar cells.[6,18]
We have demonstrated that ferroelectric poling of MAPbI3 can be achieved by application of an electric field
Summary
Earlier attempts (including our own) to electrically pole MAPbI3 employed a common solar cell architecture, i.e., an out-of-plane (vertical) electric field applied across a layer stack, which often led to a destruction of the perovskite layer. We used the two-step deposition process for the MAPbI3 layer and the subsequent solvent-vapor annealing that we described in our previous reports on polar domains in perovskite solar cells.[6,18] Importantly, this sample architecture allows the direct monitoring of changes in the MAPbI3 microstructure upon poling since the MAPbI3 layer is not concealed by a counter electrode as it would be the case in a vertical poling geometry. We deliberately opted for a perovskite layer thickness of 300 nm in order to best represent the MAPbI3 layers that are typically employed in solar cells
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