Bulk-Controlled Photovoltaic Effect in Nanometer-Thick Ferroelectric Pb(Zr_0.2Ti_0.8)O₃ Thin Films and the Role of Domain Walls

Photovoltaic effect in ferroelectrics can be considered as a sum of two dominant contributions, that is, arising from the ferroelectric/metal junctions and from the bulk of the ferroelectrics. In the case of Pb(Zr0.2Ti0.8)O3, several studies have been devoted to analyze the contributions from the junctions and associated aspects such as barrier height. In this work, we elaborate on the contribution from the bulk, and the role of an inherent nano-sized entity, that is, domain walls. Systematic investigations were conducted with samples of different thicknesses (75–700 nm), which evidently also assisted in varying the proportion of domain walls. The open-circuit voltages scaled up with thickness in accordance with the bulk-driven photovoltaics phenomenology. Temperature-resolved measurements highlighted the influence of domain walls on the overall transport characteristics under light and dark conditions. Analysis of the spectral photoresponse unraveled the sub-band gap character of the domain walls and the prospective role in the overall photovoltaic effect.