The Multiple Roles of Metal Ion Dopants in Spectrally Stable, Efficient Quasi‐2D Perovskite Sky‐Blue Light‐Emitting Devices

Abstract Perovskite light‐emitting devices (peLEDs) have recently gained widespread attention as candidates for next‐generation display technologies. Red and green peLEDs have achieved over 20% external quantum efficiency (EQE), however blue peLEDs still lag behind. One proposed solution for improving the performance of blue peLEDs has been doping the perovskite films with metal ions, ostensibly to passivate surface trap sites and improve the EQE. Despite a few recent reports, however, the many roles of the metal ion dopants have not yet been fully explored. Here improvements in the EQE and spectral stability of quasi‐2D perovskites, often called 2D/3D or layered perovskites are reported. CsPbBr_3−xCl_x sky‐blue emitting peLEDs, with a maximum EQE of 7.5%, and color stable spectra at high applied voltages are achieved, via doping with divalent metal ions at concentrations of 0.5 to 10%, by mole ratio. After screening several candidates, two metal ions are identified, Mn²⁺ and Mg²⁺ that are particularly effective, as compared with PEA‐based quasi‐2D control devices. Then these examples are used to study the effect of metal ions more generally on the film morphology, the hole transport layer's conductivity, the trap density, and the energy funneling dynamics, all of which strongly influence the device performance.