Interest in low-temperature operation of solid oxide fuel cells is growing. Recent advances in perovskite phases have resulted in an efficient H⁺/O^2-/e^- triple-conducting electrode BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ for low-temperature fuel cells. Here, we further develop BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ for electrolyte applications by taking advantage of its high ionic conduction while suppressing its electronic conduction through constructing a BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ-ZnO p-n heterostructure. With this approach, it has been demonstrated that BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ can be applied in a fuel cell with good electrolyte functionality, achieving attractive ionic conductivity and cell performance. Further investigation confirms the hybrid H⁺/O^2- conducting capability of BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ-ZnO. An energy band alignment mechanism based on a p-n heterojunction is proposed to explain the suppression of electronic conductivity and promotion of ionic conductivity in the heterostructure. Our findings demonstrate that BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ is not only a good electrode but also a highly promising electrolyte. The approach reveals insight for developing advanced low-temperature solid oxide fuel cell electrolytes.

We demonstrate that ultrathin P-type Cu₂O thin films fabricated by a facile thermal oxidation method can serve as a promising hole-transporting material in perovskite solar cells. Following a two-step method, inorganic–organic hybrid perovskite solar cells were fabricated and a power conversion efficiency of 11.0% was achieved. We found that the thickness and properties of Cu₂O layers must be precisely tuned in order to achieve the optimal solar cell performance. The good performance of such perovskite solar cells can be attributed to the unique properties of ultrathin Cu₂O, including high hole mobility, good energy level alignment with CH₃NH₃PbI₃, and longer lifetime of photo-excited carriers. Combining the merits of low cost, facile synthesis, and high device performance, ultrathin Cu₂O films fabricated via thermal oxidation hold promise for facilitating the developments of industrial-scale perovskite solar cells.