Connor Davel
Advisors: Prof. Nazanin Bassiri-Gharb, Prof. Juan-Pablo Correa-Baena

will propose a doctoral thesis entitled,

Understanding and Inhibiting Operational Instabilities in Lead Halide Perovskites via Phosphonic Acid Additives and Interfacial Design

On

Wednesday, January 14th at 9:30 a.m.

Pettit Microelectronics Room 102A

Committee

Prof. Nazanin Bassiri-Gharb, Co-advisor – G. W. School of Mechanical Engineering (advisor)

Prof. Juan-Pablo Correa-Baena, Co-advisor - School of Materials Science and Engineering (advisor)

Prof. Lauren Garten - School of Materials Science and Engineering (advisor)

Prof. Emma Hu - School of Materials Science and Engineering (advisor)

Prof. Erik Garnett - AMOLF, The Netherlands

Abstract
Lead halide perovskites (LHPs) are an emerging low cost and high-performance family of semiconductors with exemplary properties for many optoelectronic applications. However, LHPs suffer from both ionic migration as well as extrinsic phase instabilities upon exposure to humidity, which decrease their energy conversion performance and limit their applications requiring long-term continuous operation. Ionic migration and phase transitions heavily depend on the morphology of the film, since both are enhanced by grain-boundaries. However, little is known about the structure-property relationships governing ionic migration in the bulk crystal structure, degradation at the surface of the film, and how to limit both sources of instability without significantly changing the chemistry of the halide perovskite film. In this thesis, I will focus on understanding how the mechanisms of defect transport and surface degradation impact the anisotropy of stability. After understanding the mobility and directionality of defect migration, I will study how phosphonic acid additives incorporate within the structure and bind to defects to reduce their conductivity and increase the phase stability of the photoactive -phase. This offers a novel strategy to inhibit ionic migration and extrinsic instabilities without modifying the chemistry and optoelectronic properties of the film. Finally, I will study how nonbonded interactions and hydrogen bonds between the growing LHP film and the substrate impact the morphology and defect concentration of LHP films. Lattice-matched substrates and self-assembled monolayers will be used to strongly bind to the LHP film, stabilizing the photoactive -phase and encouraging a conformal layer-by-layer growth morphology with reduced grain-boundary density. The effect of crystallographic orientation, stabilizing interactions with phosphonic acid additives, and increased substrate interactions on defect transport and stability will be analyzed with electrochemical strain microscopy and Kelvin probe force microscopy to understand how each impact the mobility of defects throughout the film.