ns2 Electron (Bi3+ and Sb3+) Doping in Lead-Free Metal Halide Perovskite Derivatives

Bi3+ and Sb3+ doping (and codoping with lanthanides) in Cs2SnCl6 vacancy ordered perovskites and Cs2MInCl6 (M = Na, K, Ag) double perovskites has been shown to open up new opportunities for solid state lighting. Bi3+ and Sb3+ with ns2 outer electronic configuration can tailor both optical absorption and emission properties for phosphor-converted light emitting diode (pc-LEDs) applications. Therefore, the s-electron dopants (Bi3+ and Sb3+) act as both sensitizers and emitters. This is because the dopant s-electrons contribute near the band edges of the host, unlike the cases of d- and f-electron dopants. Consequently, Bi3+ doping can also act as a sensitizer for lanthanide luminescence in systems like Bi3+-Ln3+ codoped Cs2AgInCl6, where Ln = Er, Yb, Tb. In this perspective, we provide insights on the tailoring of electronic and optical properties by ns2 electron doping. These insights are then connected to the rational design of hosts, dopants, and codopants, for their potential applications. Finally, we discuss challenges and opportunities for future research.