Author ORCID Identifier

https://orcid.org/0000-0001-8171-0634

Date Available

4-25-2022

Year of Publication

2022

Degree Name

Master of Science (MS)

Document Type

Master's Thesis

College

Arts and Sciences

Department/School/Program

Physics and Astronomy

First Advisor

Dr. Gamini Sumanasekera

Second Advisor

Dr. Kwok-Wai Ng

Abstract

This work seeks to understand the degradation mechanism of technically important material systems such as black phosphorene (BP), arsenic phosphorene (AsP) and Methyl ammonium lead iodide (CH3NH3PbI3) perovskite. Degradation studies were conducted by studying the in-situ electrical transport properties (resistance and thermoelectric power (TEP)) of these materials in vacuum (under annealed condition) and after exposure to the ambient air.

BP and both exhibited p-type semiconducting (positive TEP) behavior under annealed conditions and the changes in their transport properties upon exposure to ambient air can be explained as due to the charge transfer between the oxygen redox potential (of acidic moist air) and the Fermi energy (EF) of the semiconductor. The electron transfer from the semiconductor to the redox couple causes an accumulation of holes in the valence band of the semiconductor and as a result TEP increases while the resistance decreases. By comparing the in-situ transport properties of black phosphorous (BP) and , it is concluded that the EF of AsP lies closer to the valence band maximum (compared to BP) indicating lesser charge transfer. Alloying black phosphorous with arsenic (isovalent substitution) can improve the stability of black phosphorous in air.

Perovskite on the other hand showed n-type semiconductor characteristics (negative TEP) and electron transfer from the perovskite to the chemical potential of the oxygen redox couple results in an electron depletion in the conduction band. This caused a negatively decreased TEP and concomitantly increased resistance in good agreement with the model.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2022.142

COinS