Inkjet Printing NiO-Based p-Type Dye-Sensitized Solar Cells

Fabrication at low cost of transparent p-type semiconductors with suitable electronic properties is essential toward the scalability of many electronic devices, especially for photovoltaic and photocatalytic applications. In this context, the synthesis of mesoporous NiO films through inkjet printing of a sol-gel ink was investigated for the first time. Nickel chloride and Pluronic F-127, used as nickel oxide precursor and pore-forming agent, respectively, were formulated in a water/ethanol mixture to prepare a jettable ink for Dimatix printer. Multilayer NiO films were formed, and different morphologies could be obtained by playing on the interlayer thermal treatment. At low temperature (30 °C), a porous nanoparticulate-nanofiber dual-pore structure was observed. On the other hand, with a high temperature treatment (450 °C), nanoparticulate denser films without any dual structure were obtained. The mechanism for NiO formation during the final sintering step, investigated by means of X-ray photolectron spectroscopy, shows that a Ni(OH)₂ species is an intermediate between NiCl₂ and NiO. The different morphologies and thicknesses of the NiO films were correlated to their performance in a p-DSSC configuration, using a new push-pull dye (so-called "RBG-174") and an iodine-based electrolyte. Moreover, the positive impact of a nanometric NiO_x layer deposited by spin-coating and introduced between FTO and the NiO mesoporous network is highlighted in the present work. The best results were obtained with NiO_x/four layer-NiO mesoporous photocathodes of 860 nm, with a current density at the short circuit of 3.42 mA cm^-2 (irradiance of 100 mW cm^-2 spectroscopically distributed following AM 1.5).