Large photocurrent density in polycrystalline hexagonal YMnO3 thin film induced by ferroelectric polarization and the positive driving effect of grain boundary

Anomalous photovoltaic effect and switchable photovoltaic output have propelled much recent research and development of ferroelectric photovoltaic (FE-PV) materials in solar cell, photodetection and optical-read nonvolatile memory fields. However, extremely small output photocurrent density in the order of nA/cm2 or μA/cm2 is the primary problem to limit applications of FE-PV materials. Herein, a large short-circuit current density is achieved in polycrystalline hexagonal YMnO3 (h-YMO) thin film prepared by sol–gel method, which reaches 3.92 mA/cm2 under 1 sun illumination (100 mW/cm2), much larger than that of other narrow-bandgap hexagonal rare-earth manganates or ferrites epitaxial thin film materials. A systematic nanoscale analysis suggests that the grain with ferroelectric polarization and grain boundary with high conductivity are the active structures that cause the photovoltaic effect. Especially, grain boundary induces a downward band bending due to potential difference at the grain/grain boundary interface, which forms a new build-in electric field to promote carrier separation. Moreover, grain boundary as the conduction path achieves effective transport of carriers. The work demonstrates the positive effect of grain boundaries in FE-PV materials, and opens up a promising route to the development of high-performance photovoltaic materials via the combined effect of ferroelectric polarization and grain boundary. •High-photocurrent polycrystalline h-YMnO3 thin film was achieved based on a simple sol-gel method.•The short-circuit current density of the polycrystalline h-YMnO3 film is higher than the epitaxial YMnO3 film reported.•The high short-circuit current is attributed to the effect of grain boundary and ferroelectric polarization.