Charged Defects in Two-Dimensional Materials

• Grant number: 25/10506-6
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date: August 01, 2025
• End date: July 31, 2027
• Field of knowledge: Physical Sciences and Mathematics - Physics - Condensed Matter Physics
• Principal Investigator: Matheus Paes Lima
• Grantee: Mateus Bazan Peters Querne
• Host Institution: Centro de Ciências Exatas e de Tecnologia (CCET). Universidade Federal de São Carlos (UFSCAR). São Carlos , SP, Brazil
• Associated research grant: 24/08610-7 - Defects in Low dimensional Materials: a Bilateral Scientific Cooperation FAPESP and FWO, AP.R

Abstract

The study of defects in crystalline materials is fundamental to understanding and engineering their electronic and optical properties. In three-dimensional (3D) systems, defects such as vacancies, interstitials, and dislocations are well understood and play a central role in developing technologies such as semiconductors, quantum materials, and radiation-resistant materials. However, in two-dimensional (2D) materials, defects exhibit unique behaviors due to reduced dimensionality, quantum confinement, and limited dielectric screening. These factors create challenges for modeling charged defects accurately, especially in vacuum-separated supercells. Traditional models like the Jellium approximation often lead to unphysical results. Recent advances, such as the Jellium Charge Correction (JCC) and models that place compensating charges at band-edge states, have shown promise in improving accuracy and physical consistency.In addition to the intrinsic electronic modifications caused by defects, their interaction with excitons-neutral quasiparticles formed by electron-hole pairs-is especially important in 2D systems. Excitonic effects are stronger in 2D materials than in their 3D counterparts, significantly influencing their optoelectronic response. Charged defects can localize excitons, enabling quantum light emission such as single-photon sources, while mid-gap states may enhance charge carrier generation, relevant for solar cell applications. On the other hand, high defect concentrations can act as non-radiative recombination centers, degrading performance. Thus, understanding the complex interplay between defects and excitons is essential for optimizing the optical and electronic properties of 2D materials.This project focuses on investigating charged defects in 2D materials through first-principles simulations, aiming to understand their formation, stability, and effects on excitonic and optoelectronic properties. The specific objectives are:Validate the JCC method and analyze formation energies of charged point defects, studying the effect of supercell size and assessing the stability of vacancies and other defects.Explore the influence of charged defects on excitonic properties, including changes in exciton binding energy, symmetry breaking, wavefunction distribution, and exciton lifetimes.Investigate the role of charged defects at 2D/perovskite interfaces, including their impact on charge transfer, interface stability, and optoelectronic behavior.By addressing these three areas, the project combines fundamental and applied research, contributing to the design of more efficient and stable materials for next-generation optoelectronic devices. The postdoctoral researcher will collaborate closely with doctoral students, promoting knowledge exchange and strengthening the research group. The project also includes active collaboration with Prof. Juarez L. F. Da Silva (University of São Paulo, São Carlos Institute of Chemistry) and Prof. Dirk Lamoen (University of Antwerp), with the prospect of a BEPE-FAPESP research internship abroad to enhance international collaboration and deepen theoretical and methodological development.