A highly efficient Cu(In,Ga)(S,Se)2 photocathode without a hetero-materials overlayer for solar-hydrogen production

Abstract

Surface modification of a Cu(In,Ga)(S,Se)2 (CIGSSe) absorber layer is commonly required to obtain high performance CIGSSe photocathodes. However, surface modifications can cause disadvantages such as optical loss, low stability, the use of toxic substances and an increase in complexity. In this work, we demonstrate that a double-graded bandgap structure (top-high, middle-low and bottom-high bandgaps) can achieve high performance in bare CIGSSe photocathodes without any surface modifications via a hetero-materials overlayer that have been fabricated in a cost-effective solution process. We used two kinds of CIGSSe film produced by different precursor solutions consisting of different solvents and binder materials, and both revealed a double-graded bandgap structure composed of an S-rich top layer, Ga- and S-poor middle layer and S- and Ga-rich bottom layer. The bare CIGSSe photocathode without surface modification exhibited a high photoelectrochemical activity of ~6 mA·cm−2 at 0 V vs. RHE and ~22 mA·cm−2 at −0.27 V vs. RHE, depending on the solution properties used in the CIGSSe film preparation. The incorporation of a Pt catalyst was found to further increase their PEC activity to ~26 mA·cm−2 at −0.16 V vs. RHE.

RGB-Colored Cu(In,Ga)(S,Se)2 Thin-Film Solar Cells with Minimal Efficiency Loss Using Narrow-Bandwidth Stopband Nano-Multilayered Filters

“…The detailed fabrication process is presented in our previous work . Briefly, black CIGSSe absorber film was prepared by spin-coating with a paste solution with subsequent heat treatments under sulfurization and selenization atmospheres, resulting in a double band gap graded structure. , CdS buffer and i-ZnO/AZO window layers were deposited onto the CIGSSe films by chemical bath deposition and a sputtering method, respectively. The CIGSSe solar cells showed moderate efficiency of ∼12% under standard illumination (AM1.5 and 100 mW/cm 2 ).…”

Enhancing Photocathodic Performances of Particulate-CuGaS2-Based Photoelectrodes via Conjugation with Conductive Organic Polymers for Efficient Solar-Driven Hydrogen Production and CO2 Reduction

“…Photoelectrochemical water splitting and CO 2 reduction using water as an electron donor have gathered much attention as a promising candidate for methodology to convert solar energy to chemical energy. − Many efforts have been made to investigate photoelectrochemical properties of Cu-contained compounds, such as sulfides, − selenides, − and oxides. − This is because most of the Cu-containing materials exhibit a p -type semiconductor character that is indispensable for employing them as photocathodes in photoelectrochemical reactions. Among them, it has been reported that Cu-contained metal-sulfide-photocatalyst powders are useful as photocathodes to reduce H 2 O and CO 2 to H 2 and CO, respectively, under simulated solar light. − ,− ,, Moreover, their band gaps correspond to visible light and can be flexibly controlled by the formation of solid solutions. − ,,,,,− Nevertheless, photoelectrochemical performances of the particulate-based photocathodes are mostly lower than those of the thin films made by vaper deposition ,,, and precursor coating followed by either sulfurization or selenization. ,,,,, A main reason why the performances of the particulate-based photocathodes are lower is considered to be insufficient contacts between the particulate photocatalysts and a conductive substrate such as FTO (fluorine-doped tin oxide). In other words, there are many cavities between the particulates and the FTO.…”

Chemical states and local structure in Cu-deficient CuxInSe∼2 thin films: insights into engineering and bandgap narrowing

“…Copper indium selenide (CuInSe 2 ) has drawn considerable attention for its feasible applications in photovoltaic devices, such as photon absorbers in solar cells, [1][2][3][4] light-emitting diodes, [5][6][7][8] and in biological and catalysis applications. [9][10][11][12] Research on selenide compounds is particularly aimed at securing the controllability of optoelectronic properties with stable chemistry to eventually replace semiconductors that contain toxic elements such as cadmium or lead. [13][14][15] However, because ternary compounds bear inherent complexity in their structure and defect chemistry, 16,17 a full understanding of the role of intrinsic/extrinsic defects in fundamental science is yet to be achieved.…”