Implementing Solvothermally Synthesized Carbon Nanodots into Dye-Sensitized Solar Cells to Enhance External Quantum Efficiency in the Ultraviolet

Carbon nanodots (CNDs) are most known for their photoluminescent behaviors under incident exposure to ultraviolet light. Their amorphous structures consist of hydrophobic C=C carbogenic cores which are surrounded by highly polar shells of -COOH carboxyl surface functional groups where the fluorescent mechanism lies. This thesis seeks to exploit these fluorescent properties of CNDs to down-convert ultraviolet photons to a more suitable photon energy in order to increase the external quantum efficiency (EQE) of dye-sensitized solar cells (DSSCs) in the ultraviolet. In the first part of this study, the CND core-shell model and a reflux synthesis time-dependent evolving carbogenic core size are confirmed by optical measurements and real-space imaging of CNDs, derived from a fully hydrothermal reflux carbohydrate conversion of D-glucose, both before and after filtration via 20kDa molecular weight cutoff (MWCO) dialysis in water. Synthesis of these CNDs, from the bottom-up hydrothermal method, follows a complex carbohydrate chemistry with thousands of various potential byproducts. One specific carbohydrate conversion process, the production of 5 Hydroxymethylfurfural (5-HMF), is suspected by many researchers to form CNDs via aldol condensation. Despite the hydrothermal synthesis method being a facile method for 5-HMF production and condensation to form CNDs, it remains inefficient and requires dialysis as a means of filtration to remove byproducts. However, we have observed this filtration method to degrade the surface functional groups of CNDs. Likewise, for the implementation of CNDs in DSSCs, acetonitrile is the most conventient solvent instead of water (more convenient than other low density solvents such as chloroform), otherwise sorption of the dye-sensitizer molecules into the metal oxide layer is compromised, which presents a miscibility dilemma when using highly polar saccharide molecules (i.e., D-fructose) as the molecular starting point for CND synthesis. To solve this problem, the second part of this thesis outlines an improved method incorporating a Lewis acid into a solvothermal reflux reaction (consisting of acetonitrile instead of water) to enable the conversion of D-fructose into 5-HMF in acetonitrile. As a result, this solvothermal method with a Lewis acid catalyst showed fluorescent properties under ultraviolet photoexcitation between λex = 295 − 385nm with solvochromatic and inner-filtering effects which were very similar to that of CNDs derived from the strictly hydrothermal CND synthesis method in the first part of this thesis. Upon the application of these newly formed CNDs in acetonitrile into our DSSC anodes, the final part of this thesis uncovers that despite the acidity and optical density of the prepared solutions decreasing the overall efficiency of the DSSC devices, an estimated 33% increase in the ultraviolet external quantum efficiency was recorded at a photoexcitation of λex = 330nm.

Grantor dc:publisher

Creighton University

Year dc:date.issued

2023

Author dc:creator

• Markuson DiPrince, Max Kostandinos

Advisor dc:contributor.advisor

• Baruth, Andrew G.

• 5-Hydroxymethylfurfural
• Carbon Nanodots
• Dye-Sensitized Solar Cell
• External Quantum Efficiency
• Fluorescence

Statement dc:rights

• Copyright is retained by the Author. A non-exclusive distribution right is granted to Creighton University and to ProQuest following the publishing model selected above.

Language dc:language.iso

en_US

Repository record dc:identifier.uri

https://cdr.creighton.edu/handle/10504/153989

OAI identifier oai:identifier

oai:cdr.creighton.edu:10504/153989