Preparation of bipolar metal oxide charge transporting layers for perovskite photovoltaics

We present a high-energy wet-milling grinding method to prepare the NiO NPs at a room temperature and a low-temperature solution-processing method for the intercalation of Cs2CO3 into NiO, resulting in bipolar charge-carrier extraction capability for inverted (p–i–n) and conventional planar (n–i–p) PSCs. In comparison with the corresponding device featuring an HTL of NiO alone, the Cs2CO3-intercalated NiO layer exhibited enhanced electron extraction without sacrificing its hole extraction capability. This new material for bipolar charge-carrier extraction has the potential to serve as an inexpensive, scalable, and environmentally stable interconnection layer for emerging flexible tandem photovoltaic devices.