Stability Enhanced Perovskite Thin Films for Solar Energy Applications

Abstract

Organic-inorganic hybrid perovskites have gained significant attention due to their promising optical and electrical properties, particularly in photovoltaic solar cells. However, their stability under ambient conditions remains a considerable challenge. Numerous research articles have focused on various strategies to address this issue, including using mixed cations to enhance stability and modify optoelectronic properties. Encapsulation techniques have also been employed to protect perovskite solar cells from degradation caused by environmental factors. Another practical approach is the use of templates, which achieve both size control and enhanced stability since they contribute to the control of the size and shape of nanomaterials during synthesis by templating them inside the pores of materials. Various porous materials, such as mesoporous silica, microgels, polystyrene, metal-organic frameworks, and anodised aluminium oxide, can be utilised as templates for this purpose. Peptide gels can also be used as templates due to their ability to self-assemble and functionalise materials and act as a medium in the synthesis and construction of nanostructures. It is possible, then, that their network structures could be used to govern the growth of the perovskite, controlling the shape and size of the grains and also passivating defects in the perovskites. This study focused on the use of two peptide gels, specifically FEFKFEFK (F8) and FEFKFEFKK (F9), as templates for fabricating methylammonium lead iodide (MAPI) perovskite nanomaterials. Two chapters of the study explored the effects of these peptides on the size, optoelectronic properties, and stability of the fabricated MAPI perovskite-peptide “composites”. The results indicated that both F8 and F9 peptides contribute to control in the particle size of MAPI, leading to changes in its optoelectronic properties. The stability of the templated MAPI perovskite was also improved. The effect of templating increased with higher peptide concentrations, which resulted in increased fibre density and decreased network mesh size, ultimately influencing the properties of the fabricated MAPI. Notably, F9 exhibited higher solubility in the MAPI precursor, allowing for the addition of larger amounts, which further decreased the size of MAPI particles and led to a greater blue shift in photoluminescence (PL) spectra. Regarding solar cells, an optimal amount of F8 peptide was determined, and was found to improve the efficiency and stability of devices based on templated MAPI. However, exceeding this optimal amount resulted in a decrease in photocurrent, possibly due to the formation of an insulating layer that affected the transport of charge carriers to the transport layers. In addition to peptide templating, the study also investigated the use of 4-fluoroaniline (4-FA) as a treatment agent to fluorinate TiO2 surfaces and prevent or reduce carbon contamination. The results demonstrated that the fluorinated samples' surfaces exhibited increased resistance to adsorbing carbon species compared to the reference sample over the same period. However, the treatment efficiency decreased with prolonged exposure time, accompanied by fluorine loss from the surfaces, which requires further investigation.

Date of Award	31 Dec 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Andrew Thomas (Supervisor) & David Lewis (Supervisor)