Ultra-lightweight energy harvesting devices based on FeCl3 intercalated few layer graphene electrodes

Abstract

This thesis examines for the first time, the integration of FeCl3 Intercalated Few Layer Graphene (i-FLG) materials in energy harvesting devices. i-FLG has shown excellent promise in the field of optoelectronic devices, such as photodetectors and light emitting devices, thanks to its high charge carrier concentration (9x1014 cm-2), low sheet resistance (< 10 Ω/sq) and high transmittance (> 84\%). However, its integration into energy harvesting devices has not been previously explored. This thesis introduces a novel method of scaling up the i-FLG manufacture from 1 cm2 to wafer scale (36 cm2). This involved the development of a method for transferring large areas of graphene from their growth substrate (Ni) to a glass substrate, followed by the demonstration of large area functionalization of graphene by FeCl3 intercalation. Raman spectroscopy mapping of 300 µm x 300 µm areas is used to calculate a metric (PosG), related to the frequency of the G band, by which the level of intercalation in a sample can be assessed. Additional functionalization by UV/Ozone treatment is also investigated and shown to improve surface wetting of i-FLG films by the introduction of oxygen containing groups on the i-FLG surface. This was used to improve the deposition of organic layers on i-FLG, and successfully fabricate Organic Photovoltaic (OPV) devices from solution processed methods.

Two types of energy harvesting devices, OPV and Triboelectric Nanogenerators (TENG), were fabricated as the first examples of energy harvesting devices with i-FLG electrodes. i-FLG based OPV devices demonstrated superior device stability under both continuous and periodic illumination, and comparable efficiencies to commercially available Indium Tin Oxide (ITO) electrode based devices. i-FLG TENG devices outperformed pristine graphene devices in terms of both their short circuit current and open circuit voltage response. This improvement is a direct result of functionalization through intercalation with FeCl3. These results indicate that i-FLG has potential advantages for use in energy harvesting devices compared to alternative electrode materials. Further work with this material shows promise in applications as a flexible electrode for use in flexible energy harvesting devices.