A Multi-Dimensional Perspective on Electronic Doping in Metal Halide Perovskites

While research on derivatives of both bulk and low-dimensional metal halide perovskite (MHP) semiconductors has grown exponentially over the past decade, the understanding and intentional applications of electronic doping have lagged behind. In this Focus Review, we take a critical look at these challenges by considering the different potential doping routes, the advantages and pitfalls of each route, and the unique properties of MHP systems that may contribute to the inherent difficulties of realizing successful electronic doping. We specifically consider low-dimensional MHP derivatives as a case study, given that the mechanistic understanding of how defect chemistry affects electronic doping has been studied less extensively in these systems than in their three-dimensional counterparts, but we also consider lessons learned from the prototypical bulk methylammonium lead iodide perovskite semiconductor to inform our discussion. We discuss the potential roles that the partially ionic nature of the chemical bonds and the soft, polarizable nature of the lattice may play in the realization of doping in MHPs, with an emphasis on defect chemistry, redox side reactions, and polaronic stabilization. Informed by relevant case studies, we illustrate lessons taken from the literature and our own experience in an effort to provide a foundation for successful electronic doping of MHPs. We conclude that the successful realization of doped MHPs will likely hinge upon careful consideration and application of doping strategies and mechanisms that have been established in both the inorganic and organic semiconductor fields over the past several decades.