Efficient solid-state dye sensitized solar cells: The influence of dye molecular structures for the in-situ photoelectrochemically polymerized PEDOT as hole transporting material
Solid-state dye sensitized solar cells (sDSCs) with organic small molecule hole transporting materials (HTMs) have limited efficiencies due to the incomplete pore filling of the HTMs in the thick mesoporous electrodes and the low hole conductivity of HTMs. Hereby, highly efficient sDSCs with power conversion efficiency of 7.11% and record photocurrent of 13.4 mA cm-2 are reported, prepared by effectively incorporating in-situ photoelectrochemically polymerized PEDOT as HTM in combination with a multifunctional organic, metal-free dye. In order to fundamentally understand how the dye molecules affect the photoelectrochemical polymerization (PEP), the properties of the generated PEDOT and the photovoltaic performance, sDSCs based on a series of dyes are systematically investigated. Detailed comparative studies reveal that the difference between the dye redox potential and monomer onset oxidation potential plays a crucial role in the PEP kinetics and the doping density of PEDOT HTM. The structure of the dyes, functioning as an electron blocking layer, affects the charge recombination at the TiO2/dye/PEDOT interface. The analysis shows that a donor-n-acceptor dye with well-tuned energy levels and bulky structure results in an in-situ electrochemically doped PEDOT HTM with a high hole conductivity (2.0 S cm(-1)) in sDSCs, leading to efficient dye regeneration and photocharge collection. It is hoped that this work will further encourage research on the future design of new dye molecules for an efficient PEP in order to further enhance the photovoltaic performance of solid-state dye sensitized solar cells. (C) 2015 Elsevier Ltd. All rights reserved.