Microwave-assisted low temperature fabrication of ZnO thin film electrodes for solar energy harvesting
journal contributionposted on 30.10.2015, 13:39 by Nirmal Peiris, Jagdeep Sagu, Hazim Yusof, Upul Wijayantha-Kahagala-GamageUpul Wijayantha-Kahagala-Gamage
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.
TANP and KGUW would like to acknowledge the support received from Johnson Matthey Plc. and RCUK (EP/G037116/1). YHY would like to acknowledge the financial support given by the Ministry of Education of Brunei. All the authors would like to thank all the members of the ERL of the Chemistry Department at Loughborough University for their assistance.