Photoemission studies of hydrogel-perovskite composites for use in next-generation solar cells

Abstract

Organometal halide perovskites (OHPs) are considered some of the most promising materials for use in next-generation solar cells; however, poor environmental stability has limited the commercialisation of perovskite solar cells (PSCs). The development of simple, cost-effective processes to limit the degradation of OHPs is vital for widespread adoption of PSCs to be realised, as is understanding the mechanisms responsible for enhanced stability. In this thesis, the use of hydrogel additives to improve the stability and optical properties of OHPs is investigated using photoemission spectroscopies. The effects of incorporating poly(2-hydroxyethyl methacrolate) (pHEMA) in the perovskite precursor are investigated using X-ray photoelectron spectroscopy (XPS), revealing the passivation of grain boundaries by a polymer-rich surface layer and an enhancement in OHP thermal stability. Self-healing of the OHP is observed following dehydration, attributed to the retention of degradation products by the polymer overlayer which is demonstrated directly for the first time using hard XPS (HAXPES). XPS, near-edge X-ray absorption fine structure (NEXAFS) and ultraviolet photoelectron spectroscopy (UPS) are employed to study peptide hydrogel-perovskite composites. In contrast with pHEMA, the peptide is found to mix homogeneously with the OHP. X-ray diffraction (XRD) and optical spectroscopies reveal that OHP crystallites form within the pores of the peptide gel, the size of which reduce with increasing peptide concentration. The peptide composites are shown to exhibit enhanced stability to both heat and moisture, attributed to inhibited ion migration, defect passivation and reduced water ingress due to complete encapsulation of the OHP. Incorporating peptide hydrogel as an antisolvent additive is explored using XPS and UPS. Peptide-functionalised antisolvent treatment is shown to enhance the thermal stability of OHPs without significantly altering the electronic properties. Modelling of the inelastic background reveals that the peptide is homogeneously mixed with the OHP, in contrast with previous studies of antisolvent additives which report a decrease in additive concentration with increasing depth.

Date of Award	1 Aug 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Andrew Thomas (Supervisor), Wendy Flavell (Supervisor) & Patrick Parkinson (Supervisor)