Dye-Sensitized Solar Cells: Study of PEDOT-MeOH Films and Polymeric Ionic Liquid

• Main Authors: Yi-Feng Lin, 林宜鋒
• Other Authors: Kuo-Chuan Ho
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/xmds5a

碩士 === 國立臺灣大學 === 高分子科學與工程學研究所 === 104 === This thesis aimed to develop structured poly(hydroxymethyl 3,4-ethylenedioxythiophene) (PEDOT-MeOH) films as counter electrodes (CEs) and to synthesize an iodide-free polymeric ionic liquid (PIL) as gel electrolyte for the dye-sensitized solar cells (DSSCs) with low-cost, high efficiency, and long-term stability. This thesis is divided into two parts: PEDOT-MeOH films as CEs (Chapter 3) and PIL as gel electrolyte (Chapter 4). In the case of the PEDOT-MeOH films as CEs, a film of the hierarchical PEDOT-MeOH tube-coral array (TCA) was successfully synthesized via a template-free electro-polymerization technique. The PEDOT-MeOH TCA was designed to simultaneously possess (1) the enhanced conjugation on PEDOT main chain due to the electro-donating MeOH group, (2) the tube-like fast one-dimensional charge transfer pathways, and (3) the coral-like extended electro-active sites. For the application in DSSCs, PEDOT-MeOH TCA worked as an outstanding electro-catalytic CE for iodine/triiodine (I–/I3–) reduction. Thus, the DSSCs with the hierarchical PEDOT-MeOH TCA as the CE reached the highest power conversion efficiency (η) of 9.13±0.06%, which was even higher than that of the DSSC with a standard Pt CE (8.94±0.07%). Via rotating disk electrode analysis, the newly synthesized PEDOT-MeOH TCA film was found to have a lower intrinsic heterogeneous charge-transfer rate constant (k0), but extremely larger effective electro-catalytic surface area (Ae) than that of the standard Pt film. The PEDOT-MeOH TCA can be considered as a convincing replacement of the expensive Pt due to its high electro-catalytic ability, low cost, and simple fabrication process. In the case of the PIL as gel electrolyte, a polymeric ionic liquid, poly(oxyethylene)-imide-imidazolium selenocyanate (POEI-IS), was newly synthesized and used for a multifunctional gel electrolyte in a quasi-solid-state dye-sensitized solar cell (QSS-DSSC). POEI-IS has several functions: (1) acts as a gelling agent for the electrolyte of the DSSC, (2) possesses a redox mediator of SeCN−, which is aimed to form a SeCN−/(SeCN)3− redox couple with a more positive redox potential than that of traditional I−/I3−, (3) chelates the potassium cations through the lone pair electrons on the oxygen atoms of its poly(oxyethylene)-imide-imidazolium (POEI-I) segments, and (4) obstructs the recombination of photo-injected electrons with (SeCN)3− ions in the electrolyte through its POEI-I segments. Thus, the POEI-IS renders a high open-circuit voltage (VOC) to the QSS-DSSC due to its functions of (2), (3), and (4), and prolongs the stability of the cell due to its function of (1). The QSS-DSSC with the gel electrolyte containing 30 wt% of the POEI-IS in liquid selenocyanate electrolyte exhibited a high VOC of 825.50±3.51 mV and a high η of 8.18±0.02%. The QSS-DSSC with 30 wt% of POEI-IS retained up to 95% of its initial η after an at-rest stability test with the period of more than 1,000 h. This properly designed PIL paves as promising way for developing highly efficient and durable QSS-DSSCs.