Tuning Photovoltaic Performance of Perovskite Nickelates Heterostructures by Changing the A-Site Rare-Earth Element

Perovskite rare-earth nickelates (RNiO₃) have attracted much attention because of their exotic physical properties and rich potential applications. Here, we report systematic tuning of the electronic structures of RNiO₃ (R = Nd, Sm, Gd, and Lu) by isovalent A-site substitution. By integrating RNiO₃ thin films with Nb-doped SrTiO₃ (NSTO), p-n heterojunction photovoltaic cells have been prepared and their performance has been investigated. The open-circuit voltage increases monotonically with decreasing A-site cation radius. This change results in a downward shift of the Fermi level and induces an increase in the built-in potential at the RNiO₃/NSTO heterojunction, with LuNiO₃/NSTO showing the largest open-circuit voltage. At the same time, the short-circuit current initially increases upon changing the A-site element from Nd to Sm. However, the larger bandgaps of GdNiO₃ and LuNiO₃ reduce light absorption which in turn induces a decrease in the short-circuit current. A power conversion efficiency of 1.13% has been achieved by inserting an ultrathin insulating SrTiO₃ layer at the SmNiO₃/NSTO interface. Our study illustrates how changing the A-site cation is an effective strategy for tuning photovoltaic performance and sheds light on which A-site element is the best for photovoltaic applications, which can significantly increase the applicability of nickelates in optoelectric devices.