Optical, electrical, and solar energy-conversion properties of gallium arsenide nanowire-array photoanodes
By Hu, Shu; Chi, Chun-Yung; Fountaine, Katherine T.; Yao, Maoqing; Atwater, Harry A.; Dapkus, P. Daniel; Lewis, Nathan S. & Zhou, Chongwu
Published in Energy Environ. Sci.
The Royal Society of Chemistry
2013
Abstract
Periodic arrays of n-GaAs nanowires have been grown by selective-area metal-organic chemical-vapor deposition on Si and GaAs substrates. The optical absorption characteristics of the nanowire-arrays were investigated experimentally and theoretically, and the photoelectrochemical energy-conversion properties of GaAs nanowire arrays were evaluated in contact with one-electron, reversible, redox species in non-aqueous solvents. The radial semiconductor/liquid junction in the nanowires produced near-unity external carrier-collection efficiencies for nanowire-array photoanodes in contact with non-aqueous electrolytes. These anodes exhibited overall inherent photoelectrode energy-conversion efficiencies of [similar]8.1% under 100 mW cm-2 simulated Air Mass 1.5 illumination, with open-circuit photovoltages of 590 +/- 15 mV and short-circuit current densities of 24.6 +/- 2.0 mA cm-2. The high optical absorption, and minimal reflection, at both normal and off-normal incidence of the GaAs nanowire arrays that occupy <5% of the fractional area of the electrode can be attributed to efficient incoupling into radial nanowire guided and leaky waveguide modes.