Inverted planar heterojunction (PHJ) perovskite solar cells have attracted great attention due to their advantages of low-temperature fabrication on flexible substrates by solution processing with high efficiency. Poly(3,4ethylenedioxythiophene): polystyrenesulfonate (PEDOT:PSS) is the most widely used hole transport layer (HTL)in inverted PHJ perovskite solar cells; however, the acidic and hygroscopic nature of PEDOT: PSS can cause degradation and reduce the device stability. In this work, we demonstrated that low-cost solution-processed hydrophobic copper iodide (CuI) can serve as a HTL to replace PEDOT: PSS in inverted PHJ perovskite solar cells with high performance and enhanced device stability. Power conversion efficiency (PCE) of 13.58% was achieved by employing CuI as a HTL, slightly exceeding PEDOT: PSS based device with PCE of 13.28% under the same experimental conditions. Furthermore, the CuI based devices exhibited better air stability than that of PEDOT: PSS based devices. The results indicate that low-cost solution-processed CuI is a promising alternative to PEDOT: PSS HTL and could be widely used in inverted PHJ perovskite solar cells.

Low-temperature, solution-processed cerium oxide can serve as a promising electron transport layer to replace commonly used TiO2 in planar perovskite solar cells, with high efficiency and enhanced stability.

A novel rare earth hybrid electrocatalyst, consisting of a gadolinium-doped hierarchal NiFe-layered double hydroxide, is developed for improving the OER activity.