Towards highly efficient photoanodes: the role of carrier dynamics on the photoelectrochemical performance of InGaN/GaN multiple quantum well coaxial nanowires
The carrier dynamics in highly active InGaN/GaN coaxial nanowire photoanodes were studied for photoelectrochemical water splitting applications that can provide deeper insight to enhance the photon-to-electron conversion efficiency. The carrier dynamics in InGaN/GaN multiple quantum well coaxial nanowires (MQW-CNWs) with three different quantum well (QW) thicknesses and the same barrier thickness were studied optically using temperature-dependent and time-resolved photoluminescence spectroscopies. The role of the carrier dynamics on the photoelectrochemical water splitting (PEC-WS) performance of the MQW-CNWs was also investigated. The dependence of the PEC-WS performance and carrier dynamics on the QW thickness provided results indicative of the impact of the exciton localization and the defect states in the photoanodic performance of the MQW-CNWs. Strong localization effects and defect-induced recombination have been shown using samples with a thin QW with thicknesses up to 3 nm. During the PEC-WS, the samples showed a large onset potential and a low photocurrent density that led to low incident-photon-to-current conversion efficiency (IPCE). As the QW thickness approached 6 nm, negligible localization as well as improved photoemission quality were achieved, which lead to a small overpotential and a high IPCE of approximately 15%. The result demonstrated that an efficient photoanode requires a high crystal quality and weak localization, which can be achieved through careful structural optimization.