posted on 2015-12-02, 00:00authored byLang Shen, Chunlin He, Jing Qiu, Sung-Min Lee, Abinasha Kalita, Stephen
B. Cronin, Mark P. Stoykovich, Jongseung Yoon
We studied a type of nanostructured
silicon photocathode for solar
water splitting, where one-dimensionally periodic lamellar nanopatterns
derived from the self-assembly of symmetric poly(styrene-block-methyl methacrylate) block copolymers were incorporated on the surface
of single-crystalline silicon in configurations with and without a
buried metallurgical junction. The resulting nanostructured silicon
photocathodes with the characteristic lamellar morphology provided
suppressed front-surface reflection and increased surface area, which
collectively contributed to the enhanced photocatalytic performance
in the hydrogen evolution reaction. The augmented light absorption
in the nanostructured silicon directly translated to the increase
of the saturation current density, while the onset potential decreased
with the etching depth because of the increased levels of surface
recombination. The pp+-silicon photocathodes, compared
to the n+pp+-silicon with a buried solid-state
junction, exhibited a more pronounced shift of the current density–potential
curves upon the introduction of the nanostructured surface owing to
the corresponding increase in the liquid/silicon junction area. Systematic
studies on the morphology, optical properties, and photoelectrochemical
characteristics of nanostructured silicon photocathodes, in conjunction
with optical modeling based on the finite-difference time-domain method,
provide quantitative description and optimal design rules of lamellar-patterned
silicon photocathodes for solar water splitting.