Hole extracting layers in perovskite solar cells: influence on performance and stability

Thesis

As one of the most promising technologies for highly efficient and low-cost photovoltaics, hybrid organic-inorganic metal halide perovskites solar cells have received a great deal of attention over the past 5 years. However, the moisture sensitivity of this material hinders commercial deployment, and the next grand challenge is now the long-term, stable operation of such devices. This thesis presents novel hole-extraction layers for perovksite solar cells, and studies their impact on both the performance and the long-term stability of the devices.

Initially, this work focuses on the development of a polymer composite hole transporting material (HTM) based on poly(3-hexylthiophene) nanowires (P3HT-NW) embedded in an inert poly(methyl methacrylate) (PMMA) matrix. This HTM gives superior efficiency when compared to a neat P3HT HTM, and outperforms conventional HTM systems after thermal stressing in air. Next, the commonly employed and unstable lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) p-dopant for 2,2’,7,7’-tetrakis(N,N’-di-p-methoxyphenylamine)-9,9’-spirobifluorene (spiro-OMeTAD), is successfully replaced by two molybdenum tris(dithiolene)s. These devices show a substantial enhancement of the long-term stability, due to a significant enhancement of the moisture resilience of the HTM layer while maintaining high device power conversion efficiencies. Finally, the interaction of these molybdenum complexes with the perovskite is studied. This study demonstrates that the molybdenum complex modifies the treated interface in two ways; it passivates surface defects and creates an interfacial dipole. As a result, the perovskite/HTM interface shows greater hole selectivity resulting in a substantial enhancement of the device performance, underscoring the importance of the charge-selective interfaces for carrier extraction.

Authors: Pellaroque, A

• DOI: 10.5287/ora-2r0kz7adb
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English