Microwave-assisted low temperature fabrication of ZnO thin film electrodes for solar energy harvesting

Abstract

Metallic Zn thin films were electrodeposited on fluorine-doped tin oxide (FTO) glass substrates and oxidized under air by conventional radiant and microwave post-annealing methods to obtain ZnO thin film electrodes. The temperature of each post-annealing method was varied systematically and the photoelectrochemical (PEC) performance of electrodes was evaluated. The best photocurrent density achieved by the conventional radiant annealing method at 425°C for 15 min was 93 μA cm −2 at 1.23 V vs. NHE and the electrode showed an incident photon-to-electron conversion efficiency (IPCE) of 28.2%. X-ray diffractogram of this electrode showed that the oxidation of Zn to ZnO was not completed during the radiant annealing process as evident by the presence of metallic Zn in the electrode. For the electrode oxidized from Zn to ZnO under microwave irradiation, a photocurrent of 130 μA cm −2 at 1.23 V vs. NHE and IPCE of 35.6% was observed after annealing for just 3 min, during which the temperature reached 250°C. The photocurrent was 40% higher for the microwave annealed sample; this increase was attributed to higher surface area by preserving the nanostructure, confirmed by SEM surface topographical analysis, and better conversion yields to crystalline ZnO. Overall, it was demonstrated that oxidation of Zn to ZnO can be accomplished by microwave annealing five times faster than that of conventional annealing, thus resulting in a~75% power saving. This study shows that microwave processing of materials offers significant economic and performance advantages for industrial scale up.

Rapid Microwave-Assisted Self-Assembly of a Carboxylic-Acid-Terminated Dye on a TiO2 Photoanode

“…It is common knowledge that microwave energy is strongly absorbed by conductive films, which, as a consequence, are heated. The heating is primarily due to the generation of an electromagnetic field and resulting induced eddy current on the film surface that is responsible for the Joule effect. , This phenomenon is well-known and has been widely used to promote annealing, sintering, synthesis, and deposition of different materials on conductive substrates such as fluorine-doped tin oxide (FTO) and indium-doped tin oxide (ITO). − Since the glass substrates employed for the photoanodes preparation are coated with a conductive FTO layer, we expect its interaction with the microwave radiation. Indeed, we noticed that a small number of the TiO 2 electrodes subjected to MWAS were damaged.…”