Sb2Se3 has recently spurred great interest as a promising light‐absorbing material for solar energy conversion. Sb2Se3 consists of 1D covalently linked nanoribbons stacked via van der Waals forces and its properties strongly depend on the crystallographic orientation. However, strategies for adjusting the anisotropy of 1D Sb2Se3 nanostructures are rarely investigated. Here, a novel approach is presented to fabricate 1D Sb2Se3 nanostructure arrays with different aspect ratios on conductive substrates by simply spin‐coating Sb‐Se solutions with different molar ratios of thioglycolic acid and ethanolamine. A relatively small proportion of thioglycolic acid induces the growth of short Sb2Se3 nanorod arrays with preferred orientation, leading to fast carrier transport and enhanced photocurrent. After the deposition of TiO2 and Pt, an appropriately oriented Sb2Se3 nanostructure array exhibits a significantly enhanced photoelectrochemical performance; the photocurrent reaches 12.5 mA cm−2 at 0 V versus reversible hydrogen electrode under air mass 1.5 global illumination.

Sb2Se3 nanoneedles for use as a photocathode for water splitting are fabricated by facile spin-coating. After sequential surface modification with n-TiO2 and Pt, a remarkable photocurrent of 2 mA cm−2 at 0 VRHE is realized.

To realize economically competitive hydrogen production through photoelectrochemical (PEC) water splitting, it is essential to develop an efficient photoelectrode consisting of earth-abundant constituents in conjunction with low-cost solution processing. Cu2ZnSnS4 (CZTS) has received significant attention as a promising photocathode owing to its abundance and good absorption properties. However, the efficiency of the solution-processed CZTS photocathode is not yet comparable to its counterparts. Here, a hybrid ink, obtained by careful control of precursor mixing order, was used to produce a highly efficient CZTS photocathode. The molecular chemistry-controlled hybrid ink formulation, particularly the roles of thiourea–Sn2+ complexation, was elucidated by liquid Raman spectroscopy. The hybrid ink-derived CZTS thin films modified with conformal coating of an n-type TiO2/CdS double layer and a Pt electrocatalyst achieved an exceptionally high photocurrent of 13 mA cm–2 at −0.2 V versus a reversible hydrogen electrode under 1 sun illumination. The modified photocathodes showed relatively stable H2 production with faradaic efficiency close to unity.

Solar-energy conversion by photoelectrochemical (PEC) devices is driven by the separation and transfer of photogenerated charge carriers. Thus, understanding carrier dynamics in a PEC device is essential to realizing efficient solar-energy conversion. Here, we investigate time-resolved carrier dynamics in emerging low-cost Sb 2 Se 3 nanostructure photocathodes for PEC water splitting. Using terahertz spectroscopy, we observed an initial mobility loss within tens of picoseconds due to carrier localization and attributed the origin of carrier localization to the rich surface of Sb 2 Se 3 nanostructures. In addition, a possible recombination at the interface between Sb 2 Se 3 and the back contact is elucidated by time-resolved photoluminescence analysis. We also demonstrated the dual role of the RuO x co-catalyst in reducing surface recombination and enhancing charge transfer in full devices using intensity-modulated spectroscopy. The relatively low onset potential of the Sb 2 Se 3 photocathode is attributed to the sluggish charge transfer at a low applied bias rather than to fast surface recombination. We believe that our insights on carrier dynamics would be an important step toward achieving highly efficient Sb 2 Se 3 photocathodes.

Although antimony triselenide (Sb2Se3) has been intensively investigated as a low-cost p-type semiconductor for photoelectrochemical (PEC) water splitting, most previous studies focused on only the top interface of Sb2Se3 photocathodes. Herein, a solution-processed Cu-doped NiO x (Cu:NiO x ) thin film is proposed as an effective bottom contact layer for the Sb2Se3 photocathode. The photocurrent density of the Sb2Se3 photocathode is improved to a record-high level of 17.5 mA cm–2 upon the insertion of Cu:NiO x capable of blocking the recombination at the back interface, while facilitating hole extraction. Electrochemical impedance spectroscopy and intensity-modulated photocurrent spectroscopy, in conjunction with other observations, indicate that the enhanced photocurrent is due to the improved quality of the bottom contact without a noticeable change in the top interface. This study not only provides new insight into the role of the bottom contact layer in photocathodes, but also is an important step toward efficient PEC H2 production via a solution-processable Earth-abundant photoelectrode.

We demonstrate organic residue free, bandgap-graded Cu 2 Zn(Sn 1−x Ge x )S 4 (CZTGeS) thin-film solar cells based on metal chalcogenide complex (MCC) ligand capped nanocrystals (NCs). The bandgap of the CZTGeS films is tuned by varying the amount of Sn 2 S 6 4− MCC ligand absorbed on the surface of the Cu 2 ZnGeS 4 (CZGeS) NCs, without an undesirable postselenization process. Using CZGeS NCs inks with three different Sn/(Ge+Sn) ratios, bandgap-graded CZTGeS thin films are obtained via multicoating and annealing procedures. Compositional and spectroscopic analyses along the film thickness confirm that the bandgraded CZTGeS absorber layer, with a gradually increasing bandgap from the back contact to the p−n junction, is successfully accomplished. Compared with an ungraded band structured CZTGeS cell, this normal grading structure facilitates both higher short circuit current and open-circuit voltage, facilitating a power conversion efficiency of 6.3%.

We present a novel solution-based synthesis method enabling the morphology variation of Sb2Se3 light absorbers. The morphology of Sb2Se3 films varies from dense particulate planar films to one-dimensional nanowire-stacked films upon modulating the Sb and Se molar ratio in the precursor ink. The effect of morphology and crystallographic orientation on the electrical and consequently the PEC properties of Sb2Se3-based photocathodes is investigated. Sequential deposition of CdS as a buffer layer with TiO2 and Pt enables us to build a favorable band structure. An onset potential of 0.47 V versus a reversible hydrogen electrode (RHE) is observed with 13.5 mA cm–2 at 0 V versus a RHE under air mass 1.5 global illumination in a pH 1 electrolyte. In addition, the surface-modified photocathode stably produces hydrogen with a photocurrent of 11 mA cm–2 at 0 V versus RHE in a neutral electrolyte, thus demonstrating the promising potential of the proposed Sb2Se3 photocathodes as efficient PEC water-splitting devices.

Solution processing of earth-abundant Cu2ZnSn(S1-x,Sex)4 (CZTSSe) absorber materials is an attractive research area in the economical and large-scale deployment of photovoltaics. Here, a band-gap-graded CZTSSe thin-film solar cell with 7.1% efficiency was developed using non-toxic solvent-based ink without the involvement of complex particle synthesis, highly toxic solvents, or organic additives. Despite the high series resistance due to the presence of a thick Mo(S,Se)x layer and Zn(S,Se) aggregates, a high short-circuit current density (JSC) was generated. In addition, there was no significant difference in open circuit voltages (VOC) between CZTS (0.517 V) and CZTSSe (0.505–0.479 V) cells, despite a significant band gap change from 1.51 eV to 1.24 eV. The high JSC and less loss of VOC are attributed to the effect of band gap grading induced by Se grading in the CZTSSe absorber layer. Our environmentally benign ink approach will enable the realization of low-cost, large-area, high-efficiency thin-film solar cells.