Formation pathways and phase behaviour of CsPbI2Br: toward stable and reproducible solar sells
File(s)
Author(s)
Alhabshi, Esra
Type
Thesis
Abstract
Despite the progress in Cs-based perovskites, fabricating reproducible, phase-pure Cs-based perovskites, specifically CsPbI₂Br films under ambient conditions remains challenging. Existing methods rely on glovebox processing and antisolvents, limiting scalability. There is aneed to understand how hold time, temperature, and cooling rates govern crystallisation pathways, void formation, film energetics, and device performance. In this thesis, we introduce the concepts of pre-annealing hold-time and temperature (Ch. 4) and warm-air-assisted, slow- cooling processing (Ch. 5), which aim to improve reproducibility and ambient-air stability. In the pre-annealing hold-time and temperature study, we systematically controlled pre- annealing hold times (0-40 minutes) and temperatures (RT and 10-20 °C). Through in-situ XRD and FTIR, we clarify the role of the pre-annealing hold time, and through combined SEM, void distribution analysis, and solar cell performance evaluation, we conclude that a hold step at 15 °C yields the highest performance and reproducibility. In the warm-air-assisted, slow- cooling processing project, we employed 50 °C warm air during spin-coating to achieve air- stable films. We also investigated the impact of the annealing time and cooling rate on the final film quality. We distinguished between the impact of p-type doping through the incorporation of oxygen and the effect of relieving strain through slow-cooling on the photoluminescence of the film and hence on the solar-cell performance.
Version
Open Access
Date Issued
2025-09-27
Date Awarded
2026-03-01
Copyright Statement
Attribution-NonCommercial 4.0 International Licence (CC BY-NC)
License URL
Advisor
McLachlan, Martyn
Publisher Department
Department of Materials
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)