Nanofabrication of uniform and stabilizer-free self-assembled platinum monolayers as counter electrodes for dye-sensitized solar cells

Abstract

We report a two-step dip-coating approach for the fabrication of self-assembled monolayers of platinum nanocrystals (SAM-Pt) with a particle size of ∼3 nm and that are uniformly deposited on a transparent conducting oxide (TCO) surface to serve as a counter electrode (CE) for dye-sensitized solar cells (DSSCs). In the first step, we prepared a polyol solution containing H2PtCl6 and ethylene glycol at 110 °C, in which the reduction kinetics were controlled by adding various proportions of NaOH. In the second step, we immersed a thiol-modified TCO substrate into the polyol solution with monodispersed Pt nanoparticles prepared at pH 3.7 at approximately 295 K to complete the nanofabrication. The DSSC devices using Z907 dye as a photosensitizer and the CE prepared using this SAM-Pt approach attained notable photovoltaic performance (η=9.2%) comparable with those fabricated using a conventional thermal decomposition method (η=9.1%) or a cyclic electrodeposition method (η=9.3%) under the same experimental conditions. We emphasize that the SAM-Pt films feature a clean surface, uniform morphology, narrow size distribution, small Pt loading and great catalytic activity; the present approach is hence not only suitable for DSSCs but also applicable for many other energy-related applications that require platinum as an efficient catalyst. Eric Wei-Guang Diau and colleagues at National Chiao Tung University in Taiwan have developed a technique to fabricate uniform platinum layers as electrodes for solar cells. Platinum is a catalyst that plays an important role in many electrochemical applications such as water splitting, fuel cells and solar cells. However, the thick films of platinum that are used add cost to these devices. The researchers have reduced this cost by developing a self-assembly method to deposit monolayers of platinum nanoparticles with a mean size of 3 nanometers at room temperature. The method involves functionalizing an electrode substrate with molecules that specifically attach to the platinum nanoparticles. Hence, when the electrode is dipped into a solution of platinum nanoparticles well prepared by controlling the pH values, a uniformly covered surface forms. In initial tests, these electrodes show very good photovoltaic properties, making the new fabrication technique even more attractive. A novel two-step approach is presented for the fabrication of self-assembled monolayers of platinum nanocrystals (SAM-Pt) uniformly deposited on a transparent conducting oxide (TCO) surface to serve as a counter electrode (CE) for dye-sensitized solar cells (DSSCs). A true self-assembled Pt nanocrystalline monolayer with a mean particle size of ∼3 nm at facet {111} was unambiguously observed in the high-resolution TEM images. We emphasize that the SAM-Pt films feature a clean surface, uniform morphology, narrow size distribution, small Pt loading and great catalytic activity; the present approach is hence not only suitable for DSSCs but is also promising for many other energy-related applications that require platinum as an efficient catalyst to expedite the oxygen reduction reaction (ORR).