Khari M. Fletcher

(Advisor: Prof. Juan-Pablo Correa-Baena)

will propose a doctoral thesis entitled,

Processing–Chemistry–Structure–Property Relationships at Metal–Halide Perovskite

Interfaces for Lightweight Photovoltaics

on

Thursday, December 10, 2026, 

at

3:00 p.m.

in

Manufacturing Related Disciplines Complex (MRDC) Room 4211

Abstract

Perovskite solar cells (PSCs) combine high efficiency with the potential for low-cost fabrication.

Reducing module weight could make them easier to transport and deploy while lowering demands on supporting structures. Conventional PSCs, however, are typically built on heavy, fragile glass coated with a transparent conductive oxide (TCO). Aluminum (Al) alloys offer a lightweight, conductive alternative, but replacing the glass and TCO with Al introduces a new Al–electron transport layer (ETL) interface. This thesis will investigate how that interface affects carrier extraction, device performance, and stability.

The first research thrust develops PSCs on Al substrates. I fabricated devices by sequentially depositing the ETL, perovskite, hole transport layer, and top electrode on Al substrates (Al-ETL PSCs). Here, I will discuss dark and one-sun current–voltage measurements and what they reveal about device performance and carrier extraction across the Al–ETL interface. The results showed a negligible short-circuit current extraction for Al-ETL PSCs, which we attribute to a carrier extraction barrier at the interface caused by native oxide (n-AlOx) formation on the Al surface. We characterized the interfacial composition and energetics using X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and reflection electron energy loss spectroscopy (REELS) techniques, which indicated the presence of an electrically insulating n-AlOx. These findings led us to investigate indium tin oxide (ITO) as a conductive interlayer to circumvent the extraction barrier. By depositing ITO on Al substrates, we fabricated Al-ITO-ETL PSCs and compared their performance with that of Al–ETL PSCs. The Al-ITO-ETL PSCs exhibited higher short-circuit currents, supporting our hypothesis that n-AlOx at the Al surface prevents carrier extraction across the Al–ETL interface.

In my second research thrust, I aim to improve carrier extraction across the Al-ETL interface without an ITO layer, which complicates scale-up. I propose to do this by reducing the n-AlOx on

the Al surface. I hypothesize that a sequence of acid-base reactions involving the Al substrate, a strong acid, and the ETL precursor will dissolve n-AlOx, expose underlying Al metal sites, and promote direct Al–ETL bonding, improving carrier extraction in PSCs [1]. I will carry out X-ray absorption spectroscopy to probe local bonding at treated and untreated Al-ETL surfaces. I will

investigate how the treatment affects the composition, structure, morphology, and energetics of the Al surface and Al–ETL interface using XPS, near surface X-ray diffraction, scanning electron

microscopy, UPS and REELS respectively. Finally, I will assess the effect of the treated interface on device performance using current-voltage measurements. The studies undertaken in this thesis aim to investigate processing-chemistry structure-property relationships of the engineered interface, the impact of these factors on PSC performance, and provide design principles for integrating metal substrate-electrodes into lightweight, mechanically robust perovskite photovoltaics.

References:

[1] Franke, M.D., Ernst, W.R. and Myerson, A.S. (1987), Kinetics of dissolution of alumina in

acidic solution. AIChE J., 33: 267-273. https://doi.org/10.1002/aic.690330213

Committee Members:

Prof. Juan-Pablo Correa-Baena (Advisor) – School of Materials Science and Engineering

Prof. Ajeet Rohatgi – School of Electrical and Computer Engineering

Dr. Tod A. Grusenmeyer – Air Force Research Laboratory

Prof. Anju Toor – School of Materials Science and Engineering

Prof. Shucong Li – School of Materials Science and Engineering