Hierarchal Nanorod-Derived Bilayer Strategy to Enhance the Photocurrent Density of Sb₂Se₃ Photocathodes for Photoelectrochemical Water Splitting

Abstract

For practical H 2 production via photoelectrochemical (PEC) water splitting, a proper nanostructure strategy allowing sufficient light absorption and effective charge carrier transport is of immense importance. In this study, via the unique sequential use of two different molecular inks, a bilayer nanostructure for a photocathode composed of vertically oriented nanorods Sb 2 Se 3 on top of a bottom compact Sb 2 Se 3 layer is produced. The hierarchical nanorod bilayer structure possesses light-trapping ability owing to the scattering effect, resulting in the enhancement of light absorption. The bilayer Sb 2 Se 3 photocathode also exhibits better charge-transport capability owing to the synergetic effects of the favorable crystallographic orientation and the enlarged surface area of the vertically aligned nanorods. The bilayer Sb 2 Se 3 photocathode achieves a photocurrent density of nearly 30 mA cm −2 at 0 V vs the reversible hydrogen electrode. This observation implies that the proposed solution-processed Sb 2 Se 3 -based hierarchical bilayer structure is a promising candidate for an efficient PEC water splitting tandem device.

A Novel Thermochemical Metal Halide Treatment for High-Performance Sb2Se3 Photocathodes

“…The open-circuit voltage ( V OC ) of the pristine film was found to be −0.13 V vs. SCE (0.49 V vs. RHE, Supplementary Equations (S1) and (S2) ), while the V OC values of treated Sb 2 Se 3 films shifted toward more positive potentials of about −0.05 V vs. SCE (0.57 V vs. RHE, Supplementary Equation (S3) ). For most Sb 2 Se 3 -based photoelectrodes, V OC values less than 0.5 V vs. RHE have been typically reported [ 20 , 21 , 22 , 23 ]. This V OC deficiency could be related to different material aspects such as (a) low quality of the single-phase Sb 2 Se 3 , a high concentration of defects and grain boundaries along with the presence of secondary crystalline or amorphous phases, which are harmful to the device performance [ 8 , 20 , 21 , 22 , 23 ]; (b) insufficient structure optimization, e.g., lattice mismatch, and an inauspicious band offset between p-type Sb 2 Se 3 and n-type CdS grown using a chemical bath [ 22 ].…”

“…For most Sb 2 Se 3 -based photoelectrodes, V OC values less than 0.5 V vs. RHE have been typically reported [ 20 , 21 , 22 , 23 ]. This V OC deficiency could be related to different material aspects such as (a) low quality of the single-phase Sb 2 Se 3 , a high concentration of defects and grain boundaries along with the presence of secondary crystalline or amorphous phases, which are harmful to the device performance [ 8 , 20 , 21 , 22 , 23 ]; (b) insufficient structure optimization, e.g., lattice mismatch, and an inauspicious band offset between p-type Sb 2 Se 3 and n-type CdS grown using a chemical bath [ 22 ]. Several authors reported the V OC values of about 0.6 V vs. RHE measured in Na 2 SO 4 electrolytes with pH values lying between 5 and 6.5 [ 39 , 40 ].…”

“…Antimony (III) selenide (Sb 2 Se 3 ) has recently emerged as an eco-compatible and low-cost absorber material for various photo-assisted applications due to its advantageous optoelectronic properties ( E g ~1.2 eV, absorption coefficient > 10 5 cm −1 , high mobility) [ 7 , 17 , 18 , 19 , 20 , 21 ]. Besides, Sb 2 Se 3 is internally stable towards photocorrosion, and its elemental composition suggests less-complicated chemistry within the device processing compared to the multielement compounds such as CIGS and CZTS [ 7 , 10 , 22 ].…”

“…Despite significant efforts for improving the properties of typical absorber layers by various post-depositional treatments (PDTs) experienced for TFSCs [ 8 , 24 , 25 , 26 , 27 , 28 ], the procedures and their productivities of stable absorber/electrolyte interface are limited [ 29 ]. To date, most devices utilizing Sb 2 Se 3 layers exhibited parameters significantly below expectations [ 17 , 18 , 19 , 20 , 21 , 22 , 30 , 31 ]. The current record photocurrent density for compact Sb 2 Se 3 photoelectrodes has been predominantly attained by improvements in deposition methods in preference to realizing any suitable PDTs [ 22 ].…”

Atomic Sulfur Passivation Improves the Photoelectrochemical Performance of ZnSe Nanorods

“…Compared with semiconductor powder-based photocatalytic water splitting systems, photoelectrochemical (PEC) cells can effectively suppress the backward reactions, thus enabling us to collect hydrogen more easily [ 3 , 4 , 5 ]. The photocatalyst is at the core of PEC cells, and thus extensive efforts have been devoted to the development of abundant, inexpensive, nontoxic, and efficient photocatalysts [ 6 , 7 , 8 , 9 , 10 , 11 , 12 ]. Among those, colloidal semiconductor nanocrystals (NCs), with a physical size smaller than the exciton Bohr radius, offer some useful properties as compared with bulk semiconductors [ 13 , 14 , 15 , 16 , 17 ].…”