Identificação de inomogeneidades morfológicas e espectrais em perovskitas de haleto de metal

Author(s)

Charles Alves Nogueira de Almeida

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin
• Defense date: 2024-04-29

Examining board members

Luiz Fernando Zagonel; Lázaro Aurélio Padilha Junior; Jilian Nei de Freitas

• Advisor: Luiz Fernando Zagonel

Abstract

Metal Halide Perovskites (MHPs) have been attracting great interest as a sustainable alternative in the field of green energy generation and are highly promising due to their high conversion efficiency, low production cost, high charge carrier mobility, low exciton binding energy, and versatility of applications. Scientific challenges such as long-term operation stability, phase segregation, thermal stability, and moisture-induced degradation still delay its application. All these factors motivate research and study regarding this class of materials. To improve the synthesis and manufacturing of increasingly efficient Perovskite Solar Cells (PSCs), some solutions can be taken, such as the insertion of monovalent cations (Cs+) and organic molecules (FA+ and MA+) that prevent the ionic mobility and avoid charge loss through non-radiative recombinations. Furthermore, the introduction of ammonium-based organic molecules in post-surface treatments forms low-dimensional 2D perovskite structures that influence the quantum confinement regime, mitigate trap states on the surface, protect the PSC active layer, act in the passivation of defects, and improve structural and thermal stability. Despite this, little experimental data is available regarding the formation mechanisms between the 2D/3D interface of these samples, and investigation at the nanoscale is still an open question in the literature. In this work, through the mapping of optical activity obtained by the Scanning Electron Microscopy Cathodoluminescence (SEM-CL), we found that the 2D phases are spatially distributed heterogeneously both at the microscale and at the nanoscale. Also, an analysis of the CL intensity in grain boundary regions suggests a preferential accumulation of low-dimensional phases (2D, n=1 and n=2). In contrast, in regions on the grain top surfaces, they exhibit the opposite behavior. This fact corroborates hypotheses present in the literature regarding the formation mechanisms of 2D perovskites when introducing organic salts (CHEAI, PEAI, PCPEAI) and the passivation of defects in the grain boundaries by 2D perovskites, which increases the efficiency of the devices. The results offer guidance for designing more efficient and stable PSCs, advancing the next generations of photovoltaic technologies (AU)

• FAPESP's process: 22/06645-2 - Identifying morphological and spectral inhomogeneities in perovskites by luminescence and topography
• Grantee: Charles Alves Nogueira de Almeida
• Support Opportunities: Scholarships in Brazil - Master