Gram-Scale Synthesis of Catalytic Co₉S₈ Nanocrystal Ink as a Cathode Material for Spray-Deposited, Large-Area Dye-Sensitized Solar Cells

Abstract

We report the development of Co₉S₈ nanocrystals as a cost-effective cathode material that can be readily combined with spraying techniques to fabricate large-area dye-sensitized solar cell (DSSC) devices and can be further connected with series or parallel cell architectures to obtain a relatively high output voltage or current. A gram-scale synthesis of Co₉S₈ nanocrystal is carried out <i>via</i> a noninjection reaction by mixing anhydrous CoCl₂ with trioctylphosphine (TOP), dodecanethiol and oleylamine (OLA) at 250 °C. The Co₉S₈ nanocrystals possess excellent catalytic ability with respect to I^–/I₃^– redox reactions. The Co₉S₈ nanocrystals are prepared as nanoinks to fabricate uniform, crack-free Co₉S₈ thin films on different substrates by using a spray deposition technique. These Co₉S₈ films are used as counter electrodes assembled with dye-adsorbed TiO₂ photoanodes to fabricate DSSC devices having a working area of 2 cm² and an average power conversion efficiency (PCE) of 7.02 ± 0.18% under AM 1.5 solar illumination, which is comparable with the PCE of 7.2 ± 0.12% obtained using a Pt cathode. Furthermore, six 2 cm²-sized DSSC devices connected in series output an open-circuit voltage of 4.2 V that can power a wide range of electronic devices such as LED arrays and can charge commercial lithium ion batteries