First-Principles Modeling of Defects in Lead-Halide Perovskites: Best Practices and Open Issues

Lead-halide perovskites are outstanding materials for photovoltaics, showing long lifetimes of photo-generated carriers which induce high conversion efficiencies in solar cell and light-emitting devices. Native defects can severely limit the efficiency of optoelectronic devices by acting as carrier recombination centers. The study of defects in lead halide perovskites thus assumes a prominent role in further advancing the exploitation of this class of materials. The perovskites defect chemistry has been mainly investigated by computational methods based on Density Functional Theory. The complex electronic structure of perovskites, however, poses challenges to the accuracy of such calculations. In this work we review the state of the art of defects calculations in lead halide perovskites, discussing the major technical issues commonly encountered and what we believe to be the best practices. By keeping as a test case the prototype MAPbI3 compound, we discuss the impact of exchange-correlation functional on the electronic structure and on the defect 2 formation energies (DFEs), by comparing semi-local and hybrid functionals, with and without spinorbit coupling corrections. The convergence of calculated defects structures and their DFEs with respect to the simulation supercell size and the performance of commonly employed charge corrections is thus discussed. A summary of results concerning the defect chemistry of MAPbI3 is provided, providing hints onto the so called defect tolerance of this material class and casting possible scenarios to be addressed by experimental investigation