Recently, perovskites have attracted intense attention due to their high potential in optoelectronic applications. Employing perovskites as the emissive materials of lightemitting electrochemical cells (LECs) shows the advantages of simple fabrication process, low-voltage operation, and compatibility with inert electrodes, along with saturated electroluminescence (EL) emission. Unlike in previously reported perovskite LECs, in which salts are incorporated in the emissive layer, the ion-transport layer was separated from the emissive layer in this work. The layer of ionic transition metal complex (iTMC) not only provides mobile ions but also serves as an electron-injection/transport layer. Orthogonal solvents are used in spin coating to prevent the intermixing of stacked perovskite and iTMC layers. The blue iTMC with high ionization potential is effective in blocking holes from the emissive layer and thus ensures EL color saturation. In addition, the carrier balance of the perovskite/iTMC LECs can be optimized by adjusting the iTMC layer thickness. The optimized external quantum efficiency of the CsPbBr 3 /iTMC LEC reaches 6.8 %, which is among the highest reported values for perovskite LECs. This work successfully demonstrates that, compared with mixing all components in a single emissive layer, separating the layer of ion transport, electron injection and transport from the perovskite emissive layer is more effective in adjusting device carrier balance. As such, solution-processable perovskite/iTMC LECs open up a new way to realize efficient perovskite LECs.

A layer of ionic transition metal complex promotes electron injection and transport, resulting in an improved carrier balance of green CsPbBr3 perovskite/iTMC light‐emitting electrochemical cells (LECs). The optimized external quantum efficiency reaches 6.8 %, which is among the highest values reported for perovskite LECs so far. More information can be found in the Research Article by C.‐W. Lu, Z.‐P. Yang, H.‐C. Su, et al. (DOI: 10.1002/chem.202103739).

Invited for the cover of this issue are Chin‐Wei Lu, Zu‐Po Yang, Hai‐Ching Su, and co‐workers at National Yang Ming Chiao Tung University and Providence University. The image depicts electron transport for light‐emitting electrochemical cells. Read the full text of the article at 10.1002/chem.202103739.