Effect of polarization on photoexcited carrier dynamics in ferroelectric thin films

Ferroelectric materials are considered as a promising candidate for photovoltaic devices owing to spontaneous polarization which may affect the photocarrier dynamics and raise photovoltaic effect. However, the interaction mechanism between the ferroelectric polarization and the photocarrier dynamics is still unclear, which limits the practical applications of this kind of materials. Here, we used femtosecond time-resolved reflectance measurements to monitor the photocarrier dynamics of PbTi_1-xNi_xO₃ (PTNO) films with different Ni doping concentrations, therefore the samples have different ferroelectric polarizations. We found that in the PTNO films with larger polarizations, the photocurrents are higher and the photocarriers recombined slower. We deduce that the depolarization fields are stronger in films with larger polarizations, and the photogenerated electrons and holes are separated more effectively. The recombination of photocarriers is retarded and the photocurrent is improved. Our study supplies a novel way for the enhancement of photovoltaic performances of ferroelectric material.