Photoelectrochemical and Photovoltaic Performance of As-deposited Ink-based CuInS2 Heterojunction Thin Film

Abstract

In this report, we demonstrate low-temperature ink-based fabrication of CuInS2-based photoelectrodes for hydrogen production capable of producing photocurrent densities as high as 8.8 mA.cm−2. In this process, molecular ink made of metal chlorides and thiourea dissolved in methanol was spin coated onto Mo-coated soda lime glass substrates. Samples were then placed on a hot plate (sample surface temperature: 250 °C) to induce CuInS2 formation and remove the solvent and by-products. No further processing, such as high temperature sulfurization, was performed. The CuInS2 films were then integrated as photocathode for hydrogen evolution by photoelectrodeposition of Pt nanoparticles. Photocurrent density of 0.4 mA.cm−2 at 0 V vs. RHE was detected from such electrodes. However, samples coated with CdS/ZnO/ITO overlayers forming heterojunction prior to Pt deposition exhibited significant improvement of the photocurrent density, reaching 8.8 mA.cm−2 at 0 V vs. RHE, highlighting the improved charge transfer by the p-n junction formed at the CuInS2/CdS interface. The charge transfer resistance of the CuInS2/CdS/ZnO/ITO-Pt photoelectrode was almost 5 times lower than that of the CuInS2-Pt photoelectrode as revealed by electrochemical impedance spectroscopy analysis. In addition, the onset potential was shifted by ca. 0.45 V toward the anodic direction, reaching 0.75 V vs. RHE. Solar cell made of identical structure (Mo/CuInS2/CdS/ZnO/ITO) showed power conversion efficiency of 2.1% with short-circuit photocurrent density and open circuit voltage of 7.4 mA.cm−2 and 820 mV, respectively.