Structured Si/Co-P photocathodes: Designs for efficient light absorption in earth abundant solar fuels devices

Abstract

Designs for solar fuels devices frequently employ electrocatalysts integrated directly on the light-absorbing surfaces of semiconductors. Improvements that are gained in catalytic efficiency can be offset by the losses in light-conversion efficiency that result from parasitic absorption by the catalyst. We report two methods of circumventing parasitic absorption in these systems, using silicon light-absorbers decorated with electrodeposited Co-P catalyst as model integrated photocathodes. (1) Co-P catalyst films on planar silicon were restructured during operation to form nanoscale catalyst islands, which led to a doubling of the max. AM1.5 power conversion from 0.56 mW/cm^2 to 1.1 mW/cm^2• (2) Higher loadings of Co-Pon structured n+p-Si photocathodes achieved greater photon conversion efficiencies due to sepn. of the regions responsible for light absorption from regions contg. opaque catalyst. High-aspect-ratio microwires, μWs, supported on a planar photoactive substrate exhibited a short circuit c.d., Jsc, of -24 ± 4 mA/cm^2• Top performing μW-on-planar n+p-S/Co-P devices achieved ideal regenerative cell efficiencies of 3.9%, and reached an operating c.d. of -10 mA/cm^2 at a potential +310 mV vs. a reversible hydrogen electrode. These devices achieved high performance for two figures of merit that are typically anticorrelated for single-junction, all earth-abundant photoelectrodes and demonstrate important design principles for solar fuels devices.