Refining Perovskite Heterojunctions for Effective Light‐Emitting Solar Cells

Abstract Solar cells capable of light‐harvesting during daytime and light‐emission at night are multifunctional semiconductor devices with many potential applications. Here, it is reported that halide perovskite heterojunction interfaces can be refined to yield stable and efficient solar cells. The cell can also operate effectively as an ultralow‐voltage light‐emitting diode (LED) with a peak external quantum efficiency of electroluminescence (EQE EL ) of 3.3%. Spectroscopic and microscopic studies reveal that double‐heterojunction refinement with wide‐bandgap salts is key to densifying the packing of perovskite grains and enlarging the bandgaps of the perovskite surfaces that are in contact with charge‐transport semiconductors. The refined perovskite enables a simple device with dual actions of solar cells and LEDs. This type of all‐in‐one device has the potential to be used in multifunctional harvesting–storage–utilization (HSU) systems.