Sean Reinecke

Topic

Degradation and Stabilization of Perovskite Inks for Solar Cells

Department of Chemistry

Date & location

• Tuesday, May 14, 2024
• 10:00 A.M.
• Elliott Building, Room 305

Examining Committee

Supervisory Committee

• Dr. Makhsud Saidaminov, Department of Chemistry, University of Victoria (Supervisor)
• Dr. Jeremy Wulff, Department of Chemistry, UVic (Member)

External Examiner

• Dr. Samira Gharehkhani, Department of Mechanical Engineering, UVic

Chair of Oral Examination

• Dr. Kieka Mynhardt, Department of Mathematics and Statistics, UVic

Abstract

A photovoltaic cell (PV) converts photonic energy into an electrical current. A typical photovoltaic cell is a multilayer device consisting of an absorber layer, hole transporter layer (HTL), electron transporter layer (ETL), a transparent electrode and a back electrode. These devices are capable of directly translating a portion of the vast amounts of solar energy that collide with the Earth into usable electrical energy. Presently the vast majority of these devices use silicon for the absorber layer and positively or negatively doped silicon for the two charge carrier transport layers. The cost of manufacturing solar panels has dropped dramatically in the past decades, leading to their widespread adoption.

However, silicon is limited by its high manufacturing cost and indirect bandgap (the energetic and momentum difference between the valence band and conduction band in a semiconductor). Thus, there is a hunt for new semiconductor materials that do not possess the same intractable issues as silicon. One very promising emergent material is perovskite. Perovskite solar cells (PSCs) possess a number of advantages over traditional silicon devices. They can be deposited using standard wet chemical techniques and equipment, they require far lower processing energy, and they can be made thin enough to form flexible devices. These devices have seen dramatic improvement in efficiency over the few years.

Unfortunately, these devices are presently too unstable under ambient conditions for widespread adoption. They react rapidly with moisture and oxygen in the air. Formamidinium lead iodide, the highest performing variant of perovskite used in solar cells, have an unstable crystal structure at room temperature. Not only is the device unstable, but so is the ink used to deposit the solar absorbent layer.

Perovskite precursor inks suffer various forms of degradation, such as iodide anion oxidation and organic cation breakdown, hindering reliable perovskite solar cell manufacturing. This thesis will show that benzylhydrazine hydrochloride (BHC) not only retards the buildup of iodine as previously reported but also prevents the breakdown of organic cations. Through investigating BHC and iodine chemical reactions, we elucidate protonation and dehydration mechanisms, converting BHC to harmless volatile compounds, thus preserving perovskite film crystallization and solar cell performance. This inhibition effect lasts nearly a month with minimal BHC, in contrast with control inks where organic cations fully react in less than a week. This enhanced understanding, from additive stabilization to end products, promises improved perovskite solar cell production reliability.

The thesis consists of 4 chapters:

• Chapter 1 will introduce the fundamentals (structure and optoelectronic properties) of perovskite solar cells. In addition, the objectives of the thesis will be discussed at the end of this chapter.
• Chapter 2 gives an overview of the methodology used in the course of my research and images of relevant devices.
• Chapter 3 contains the results of the research and its analysis focusing on the use of, and understanding of, BHC as a stabilizer.
• Chapter 4 is a conclusion and overview of future prospective research.