Design and Characterization of High-Performance Electrodes for Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSC) have attracted much attention recently due to its potential as a cost-effective alternative for silicon-based solar cells. Three major components are involved to make a highly efficient DSSC: a working electrode containing dye-sensitized nanostructured TiO₂ layers, a counter electrode containing platinum-coated TCO substrate, and a composite electrolyte solution to fill between the two electrodes. In this lecture, I will present our recent developments on novel electrodes for highly efficient DSSC. For the counter electrodes, novel platinum nanostructures were fabricated according to a cyclic electro-deposition (CED) method for the Pt films with uniform nanograss structure having great electro-catalytic performance and intrinsic light-scattering, perfectly suitable for use as counter electrodes for DSSC. we have developed a strategy of nanofabrication to prepare monolayers of platinum nanoparticles self-assembled on a rough surface of TCO in two steps: first, preparation of a well dispersed Pt NP solution from polyol reduction at a pH well controlled on adding NaOH; second, dipping the SAM-functionalized TCO substrate, prepared beforehand using ‘piranha’ and MPTMS surface treatments in turn, into the Pt NP solution near 295 K to complete the fabrication of the SAM-Pt CE for DSSC. The uniform SAM-Pt film with a narrow distribution of size can be produced on TCO without a stabilizer, so that the traditional thermal treatment at high temperatures is no longer necessary. The uniform nature of the SAM-Pt film has the advantages of minimizing the amounts of Pt loading and optimizing the catalytic function on the TCO surface. The DSSC devices prepared according to this SAM-Pt approach attained notable photovoltaic performance (η = 9.2 %) comparable to those fabricated with a conventional TD method (η = 9.1 %) or a CED method (η = 9.3 %) under the same experimental conditions. For the working electrodes, we constructed photoanodes, containing titania nanostructures of varied types – spherical nanoparticles (NP), one-dimensional nanorods (NR), and octahedron-like nanocrystals of varied size (HD1-HD3), in either a bi-layer (BL) or a multi-layer (ML) film configuration. The ML devices were fabricated based on the NP-BL system with additional HDP layers inserted between the two components, NP and SL, to enhance J_SC so as to attain the best performance, with efficiency of power conversion (PCE) = 10.1 %, at film thickness (L) 26 mm. Because of the robust structural feature of the HD films, the devices fabricated with a simple BL film configuration, HD1/SL = 6/3, exhibited the best performance, PCE = 10.2 % at L = 29 mm, which is a promising advance for Z907-based solar cells with a superior and enduring stability of performance for commercialization.