Preparation And Performance Of One-dimensional Counter Electrode Materials For Dye-sensitized Solar Cells

Over the last three decades,dye-sensitized solar cells（DSSCs）have been widely investigated as alternatives to silicon solar cells,owing to their easy fabrication,flexible design,environmental friendliness,and good conversion efficiency under low light conditions.The counter electrode,as an important component of DSSCs,plays a role in the harvesting of electrons from the external circuit and the catalytic regeneration of the oxidation state electrolyte.Its electrical conductivity,electrocatalytic ability,and chemistry stability will greatly affect the comprehensive performance of the cell.Therefore,the preparation of novel low-cost,excellent-performance,and high-stability counter electrode materials by a relatively simple method is of great significance for the practical application of DSSCs.The one-dimensional materials,due to their one-dimensional electron transfer pathways and large specific surface area,are extremely promising for counter electrodes.In this thesis,several one-dimensional materials were prepared as counter electrodes for DSSCs.The electrocatalytic and photoelectric properties of these counter electrodes were systematically investigated.The main content of the thesis consists of the following sections:（1）A low-cost transparent electrode of Ag-Ni（core-shell）nanomaterials（Ag Ni NCs）has been designed and synthesized to replace the traditional FTO transparent electrode.The transparent network of Ag Ni NCs is formed by electrodeposition of a corrosion-resistant Ni shell on the surface of Ag NWs,and the Ag NWs can be“welded”together by the electrodeposited Ni shell at the junction,subtly reducing the contact resistance of the nanowires across the junction.This allows the as-prepared Ag Ni NCs to exhibit not only good transparency and corrosion resistance but also excellent electrical conductivity.In order to further enhance the catalytic performance of Ag Ni NCs electrodes,a layer of Pt was electrodeposited on the surface of Ag Ni NCs to prepare Ag Ni Pt NCs electrodes.Ag Ni Pt NCs electrodes have high electrical conductivity,excellent light transmission,corrosion resistance,and high catalytic activity.Furthermore,the uniform Ni shell of Ag Ni Pt NCs can let Ag NWs avoid directly contacting with the electrolyte of DSSCs,enabling the application of Ag Ni Pt NCs electrodes to DSSCs to show strong stability and high energy conversion efficiency.Therefore,Ag Ni Pt NCs can be expected as a kind of low-cost and highly efficient transparent counter electrode instead of the traditional FTO/Pt electrode for the TCO-free DSSCs.（2）Preparation of carbon fibers（CFs）by electrostatic spinning.To further improve the electrocatalytic activity of CFs,surface modification of CFs was carried out by electrochemical deposition of Pt and Ni S to obtain Pt/CFs and Ni S/CFs complexes.A transparent,flexible tape-like counter electrode with a novel structure and high performance has been exploited by adhering the synthesized CFs-based conductive material to transparent scotch tape（ST）.In addition,thermoplastic gel electrolytes（TPGE）were prepared for DSSCs to solve the leakage problem of liquid electrolytes.The performance of CFs/ST,Pt/CFs/ST,and Ni S/CFs/ST as transparent flexible counter electrodes for quasi-solid state dye-sensitized solar cells（QS-DSSCs）was systematically investigated.There are great prospects for practical applications that stable gel electrolytes and CFs-based/ST as transparent counter electrodes with superior electrochemical activity to optimize the comprehensive performance of DSSCs.（3）A new strategy for the facile synthesis of well-shaped one-dimensional Ni Se nanomaterials by ion exchange was developed and their application as electrodes for DSSCs was explored.The hydrothermal method was used to synthesize Ni（SO₄）_0.3（OH）_1.4nanobelts,and the precursor was successfully transformed into a new kind of one-dimensional porous Ni Se-NWs by ion exchange.This special synthesis process enables Ni Se nanowires to form a tightly connected network of transported electrons and a hierarchical porous structure with a large specific surface area,resulting in a convenient transfer of electrons and iodine/triiodide electrolytes.As a result,the counter electrode formed by Ni Se nanowires exhibits both good electrical conductivity and excellent electrocatalytic activity.The photovoltaic conversion efficiency of DSSCs with the as-prepared novel Ni Se nanowires as a counter electrode is 7.13%,higher than 9.52%, that of the conventional Pt electrode.This result shows it can be a potential alternative to the expensive Pt electrode in DSSCs.