Solution epitaxy of single-crystal ferroelectric p-i-n structure with ultrahigh photovoltaic response

Ferroelectric materials with a switchable polarization are appealing for optoelectronic applications because of their above-bandgap photovoltage with a potential to exceed the Shockley-Queisser limit efficiency within classic p-n junctions. However, the intrinsic photovoltaic current in ferroelectrics remains far below the junction ones by orders, hindering their practical applications. Here we report an extremely large photovoltaic current density of 130 mA cm^-2 with a photovoltage of 1.31 V under 375 nm light illumination in single-domain lead titanate films. Its photoresponsivity surpasses all available ferroelectric materials by two orders of magnitude. Systematic investigations reveal that an interfacial Ta dopant layer during solution epitaxy drives a polarization converting of the film via the flexoelectric effect, where surface charged Pb vacancy layer was generated for polarization screening. These two layers produce a p-i-n structure throughout the film, accounting for the ultrahigh photovoltaic response. Furthermore, a self-powered X-ray detector made of such film was explored to achieve a sensitivity of 4.73 C Gy_air^-1 cm^-3, three orders of magnitude higher than that of commercial amorphous Se detectors. Our findings may pave the way for exploring novel detection and imaging devices based on ferroelectric materials.