Metal oxide charge carrier transporting materials have been incorporated in many ways in perovskite solar cells (PSCs) because of their excellent chemical stability, wide band gaps, and reasonable mobilities. Herein, we report a low-temperature solution-processed intercalation method for introducing metal oxides displaying bipolar transporting capability into PSCs. We intercalated p-type nickel oxide (NiO) with cesium carbonate (Cs2CO3) to function as hole and electron transport layers for inverted (p–i–n) and conventional planar (n–i–p) PSCs, respectively. When compared with the corresponding NiO-only hole transporting layer, the Cs2CO3-intercalated NiO layer displayed enhanced electron extraction without sacrificing its hole extraction capability. The power conversion efficiencies of the inverted and conventional planar PSCs reached as high as 12.08 and 13.98%, respectively. This approach not only realizes the bipolar extraction capacity of Cs2CO3-intercalated p-type metal oxides but also opens up a possible route for preparing interconnecting layers for tandem optoelectronics.
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