Date Approved

12-2019

Graduate Degree Type

Thesis

Degree Name

Engineering (M.S.E.)

Degree Program

School of Engineering

First Advisor

Dr. Heidi Jiao

Second Advisor

Dr. Bruce Dunne

Third Advisor

Dr. Nabeeh Kandalaft

Academic Year

2019/2020

Abstract

This study aims to investigate the environmental factors that affect the performance and longterm stability of the perovskite solar cells (PSCs). PSCs are based on organo-metallic halides (perovskites) that act as a light-sensitive compound that produces excitons when placed under the light. However, PSCs have a limited operating lifetime due to the degradation of the perovskite layer. There are many factors like moisture, UV light, and temperature that lead to the degradation of the perovskite layer. From the literature review, it was found that the PSCs do not degrade with the presence of oxygen in a dry and dark environment. However, the presence of moisture along with oxygen causes an irreversible degradation of the perovskite layer.

This study aims at fabricating perovskite solar cells using two different techniques. The first technique is the spin coating technique, and the second technique is the blade coating technique. The performance and the long-term stability of the solar cells were investigated, and improved perovskite solar cells were fabricated. The improved solar cells were then tested under different environments to study the stability of these solar cells. The structure of the PSC used in this study contains the Transparent Conductive Oxide (TCO), electron transport layer (TiO2), perovskite absorber, hole transport layer, and the conductive metallic silver layer. Blade coating and spin coating methods were used to fabricate the perovskite solar cells. These solar cells were investigated under various environmental conditions like controlled humidity (30% to 38% RH), high humidity (>50% RH), nitrogen under room temperature of 22°C, and nitrogen under elevated temperature at 80°C.

The properties of solar cells studied are the optical absorption of the perovskite absorber, the open-circuit voltage (VOC), short circuit current (ISC), fill factor (FF), and efficiency of the PSCs.

The solar cells were stored under both dark and light (sunlight during the day, and room light at night) with controlled humidity (30% to 38% RH), high humidity (>50% RH), nitrogen under room temperature of 22°C and elevated temperature of 80°C. Each solar cell under different environments was tested as a function of time. It was found that high humidity, elevated temperature, and presumably the UV part of the white light caused the solar cell to degrade rapidly. It was seen that the nitrogen atmosphere with a room temperature of 22°C had the best environment for storing the perovskite solar cell. Further, the introduction of Al2O3 as a buffer layer and an epoxy resin increased the stability of the solar cell.

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