No abstract

We monitored the evolution in time of pinhole-free structures based on FTO/TiO/CHNHPbICl layers, with and without spiro-OMeTAD and counter electrodes (Ag, Mo/Ag, and Au), aged at 24 °C in a dark nitrogen atmosphere. In the absence of electrodes, no degradation occurs. While devices with Au show only a 10% drop in power conversion efficiency, remaining stable after a further overheating at 70 °C, >90% is lost when using Ag, with the process being slower for Mo/Ag. We demonstrate that iodine is dislocated by the electric field between the electrodes, and this is an intrinsic cause for electromigration of I from the perovskite until it reaches the anode. The iodine exhaustion in the perovskite layer is produced when using Ag electrodes, and AgI is formed. We hypothesize that in the presence of Au the iodine migration is limited due to the buildup of I negative space charge accumulated at the perovskite-OMeTAD interface.

A model for Metal-Ferroelectric-Metal structures with Schottky contacts is proposed. The model adapts the general theories of metal-semiconductor rectifying contacts for the particular case of metal-ferroelectric contact by introducing: the ferroelectric polarization as a sheet of surface charge located at a finite distance from the electrode interface; a deep trapping level of high concentration; the static and dynamic values of the dielectric constant. Consequences of the proposed model on relevant quantities of the Schottky contact such as built-in voltage, charge density and depletion width, as well as on the interpretation of the current-voltage and capacitance-voltage characteristics are discussed in detail.

No abstract

Ferroelectric single–crystalline PbZr0.2Ti0.8O3 thin films, free from extended defects, are grown by pulsed laser deposition onto vicinal SrTiO3(001) single crystals. The PbZr0.2Ti0.8O3 films are strained and exhibit enhanced tetragonality, c/a ≈ 1.06. They have a remnant polarization, Pr ≈ 110 μC cm–2, dielectric constant, ϵ33 ≈ 90, and piezoelectric coefficient, d33, up to 50 pm V–1 (see figure).