Electrode materials for stable perovskite solar cells

Thesis

Countering climate change requires a shift to renewable energy, with perovskite solar cells (PSCs) bound to play a crucial role. Ensuring the longevity of PSCs is important to enable their sustainable and reliable use. Research into improving PSC stability has primarily focused on the perovskite active layer, while the role of electrode materials and their interfaces remains underexplored. This thesis investigates the impact of different electrode materials on PSC stability, providing insights into interfacial energetics and material compatibilities, enabling future device design.

Firstly, I examined the interface energetics between carbon-based electrodes and the electron transport layer (ETL) in p-i-n PSCs. I reveal that blade-coated carbon electrodes exhibit unexpected semiconducting behaviour at the ETL interface, leading to preferential hole extraction. These findings explain the common use of carbon electrodes for hole-, rather than electron-, extraction. Additionally, I identify fundamental incompatibilities with commonly used ETLs. Based on this, I developed the first p-i-n PSCs without evaporated layers, incorporating atomic layer deposition (ALD) of SnO₂ and a conductive polymer interface modifier to improve ETL/carbon contact. I further demonstrate the first p-i-n PSCs with laminated carbon electrodes, achieving strongly enhanced stability compared to blade-coated counterparts. Additionally, I show that laminated graphene encapsulation enhances perovskite thin film stability by orders of magnitude compared to films without graphene.

Subsequently, I present the first direct comparison between indium tin oxide (ITO) and fluorine-doped tin oxide (FTO) transparent electrodes, revealing a significant advantage of FTO in long-term device stability. In a systematic study, I identify indium ion leaching from ITO into the perovskite layer as a probable factor accelerating light- and heat-induced degradation. Finally, I examine the stability of metal electrodes (gold, silver, aluminium, and copper), with and without a chromium interlayer. A chromium-aluminium bilayer electrode improves device stability beyond gold while reducing raw material costs by five orders of magnitude.

These findings deepen the understanding of electrode-induced degradation in PSCs and provide practical design strategies to enhance device stability while reducing material and deposition costs.

Authors: Lukas, T

• DOI: 10.5287/ora-bpo8y2o7b
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: electrodes; graphene; photovoltaics; p‑i‑n architecture; stability; interface engineering; perovskite; solar cell; carbon; long‑term reliability
• Subjects: Condensed matter; Diodes, Semiconductor; Perovskite solar cells; Physics