Date of Award

Spring 2018

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Electrical/Computer Engineering

Committee Director

Gon Namkoong

Committee Member

Christopher Bailey

Committee Member

Helmut Baumgart

Abstract

Perovskite solar cells (PSCs) have the potential to replace the traditional silicon solar cells for commercialization applications. Perovskites offer a lower cost to fabrication, superb efficiencies, high absorption coefficients, longer carrier lifetime and diffusion lengths. Despite their improved efficiency, perovskites suffer from several degradations relating to the material’s organic-inorganic composition upon exposure to different environmental conditions. In general, the main causes of degradation of perovskite films are due to exposure to moisture, oxygen, air, light, and temperature. Several efforts have been made to stabilize perovskites including encapsulation, doping of cations, and alterations to the perovskite structure. In this work, we study the effect of PMMA and cesium (Cs) on the thermal stability of perovskite solar cells.

Due to the organic composition of perovskite solar cells (PSCs), the material has high sensitivity to moisture, air, oxygen, light and heat. Upon exposure to these sensitive factors, perovskite films undergo degradation very quickly, resulting in a reduced efficiency and unstable cell. To better improve the material’s stability, we study the effect of adding a PMMA layer on top of the MAPbI3 samples, induced at 85°C to study whether PMMA has a major effect not only in protecting the layer from degradation factors, but also on its thermal stability. XRD measurements confirmed that samples without the PMMA layer quickly showed signs of degradation after 72 hours of heating with the peak formation of PbI2. MAPbI3 samples with the PMMA were able to withstand heating up to 1000 hours with minor sign of the PbI2 peak. SEM images confirmed the degradation of the samples without PMMA as indicated by pinholes forming along the grain boundaries and grain of the samples, while samples with the PMMA showed very little signs of degradation.

We further studied the thermal stability of perovskite solar cells by heating the samples at a more aggressive temperature (120°C) and study the effects of cesium on the precursor solution. Due to MAPbI3’s susceptibility to degradation at higher temperatures, cesium was added to the precursor solution at different concentrations (x = 5, 9 and 20%) to form the CsxMA1−xPbI3 formula. XRD data showed that after 72 hours of thermal treatment, samples with the cesium content withheld the perovskite samples from complete degradation. Data for the MAPbI3 reference sample showed complete degradation after the 72 hours, as indicated by the very intense peak formation of PbI2.

ISBN

9780438022072

ORCID

0000-0003-3027-3002

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