Materials Modeling of Halide Perovskites and Related Compounds

Abstract

Halide perovskites have emerged from a decade ago with soaring eciencies in optoelectronicapplications, competing with many traditional inorganic semiconductors. Despitetheir excellent performance in laboratories, issues such as toxicity, stability, defectsproperties have to be addressed in order for perovskites to be employed in real worldapplications. First-principles calculation is a powerful yet relatively inexpensive wayto investigate their physical properties. This thesis focuses on modeling the materialschemistry and physics of a class of inorganic halide perovskites and related compounds.The results consist of three chapters.The rst results chapter aims to design new materials beyond halide perovskites withearth abundant, non-toxic, high eciency materials. Antimony suldes, cesium antimonysuldes and methylammonium antimony suldes are reported, which exhibitsuitable band gaps, dispersive band structure and comparable work function to hybridperovskites.The second results chapter focuses on the phonon properties and soft modes of 24 dierentinorganic halide perovskites. It is shown, through lattice dynamics calculation, thatall these inorganic perovskites are unstable at their cubic phase, a confusion often arisenin conicting experimental measurements. The anharmonic energy surface is computedto quantify the strength of the instabilities and correlate with the chemical compositionand crystal structure. Dierent types of instabilities are also categorised according to theirreducible representations, the occurrence of which depends on the chemical identity.The last results chapter investigates the vacancy defects of 9 commonly synthesisedinorganic halide perovskites. We have calculated the formation diagram, neutral vacancyformation energy at dierent synthesis conditions, and charged defect formation energyas a function of the Fermi level. The results show that these perovskites are defecttolerant, i.e. they do not tend to form deep level trap states, which are detrimental foroptoelectronic devices. To link this chapter with the previous chapter, we calculate therelaxation energy and correlate it to the formation energy of the defects, and found thatthere is a negative relationship between the two. This sheds light on the eect of \giant"relaxation energy on the formation of defects.All the work has been compared with experiments, if available, and shown good agreements.The understanding developing from our rst-principles simulations have importantimplications for optoelectronic applications for these materials.

Date of Award	26 Sept 2018
Original language	English
Awarding Institution	University of Bath
Supervisor	Aron Walsh (Supervisor) & Jonathan Skelton (Supervisor)