In-situ formation of dispersed ZnO nanoparticles in mesoporous carbon counter electrode for efficient dye-sensitized solar cells

• ZnO is introduced into MC counter electrode as binder by in-situ formation.
• The annealing temperature to obtain a high-performance electrode is 300 °C.
• The efficiency of ZnO–MC based DSC is 14.2% higher than that of CMC–MC based one.
• ZnO–MC electrode used in DSC has comparable performances to Pt electrode.
• High property is due to ZnO improved MC film and suitable characteristics of MC.

The high electronic-mobility ZnO was developed as binder with a mesoporous carbon (MC) as catalytic material to fabricate a novel ZnO–MC counter electrode through in-situ formation technique. The homogeneous MC blended paste containing the ZnO sol was first coated on the conductive substrate, and then annealed in ambient atmosphere to obtain the ZnO–MC electrode. The annealing temperature is a key factor to obtain the high-performance ZnO–MC electrode. When annealed at 300 °C, the in-situ formed and dispersed ZnO nanoparticles are functioned as bridges to bind the MC particles and to strengthen the adhesion of the carbon film to the substrate, providing enough conductive paths for the transportation of the electrons to participate timely in the reduction of tri-iodide (I3−), and further improving the electrochemical performances of the electrode. As a result, the efficiency of the ZnO–MC electrode for use in dye-sensitized solar cells (DSCs) enhances from 2.5% to 6.37% compared with the binder-free MC electrode. Importantly, the ZnO–MC electrode exhibits higher catalytic activity for the I3− reduction than the MC electrode using carboxymethyl cellulose (CMC) as binder, leading to an increase of 14.2% in the efficiency of the cell, which is mainly from the high electronic-mobility of the ZnO. Furthermore, the efficiency of the low cost ZnO–MC based DSCs reaches 90.4% of that of the Pt based ones. Noted that compared with the Pt electrode, the ZnO–MC electrode is beneficial to obtain a device with higher open-circuit voltage.