Metal-free Sensitizers Approach for High Performance Dye-sensitized Solar Cells

• Main Authors: Yeh-Yung Lin, 林燁雍
• Other Authors: 何國川
• Format: Others
• Language: en_US
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/60806421969967380874

博士 === 國立臺灣大學 === 化學工程學研究所 === 102 === New organic dyes were developed and used as the sensitizers for the dye-sensitized solar cells (DSSCs). Different approaches (co-sensitized, co-adsorbent, zinc oxide photoanode) were used to improve the cell performance. Various physical measurements, including UV–vis absorption spectroscopy, electrochemical impedance spectroscopy (EIS), and incident photo–to–current conversion efficiency (IPCE) spectra, charge extraction method (CEM) and intensity-modulated photovoltage spectroscopy (IMVS) were used to obtain important parameters relevant to the cell performance for correlation between the molecular structure and the cell performance. Bipolar organic dyes containing a 9,10-dihydrophenanthrene entity in the conjugated bridge were synthesized as the sensitizers for DSSCs. The DSSC exhibits good cell efficiencies ranging from 5.21% to 5.95% under 1 sun condition. When combining the best performed dye (BP-2) with a squaraine dye (SQ2), the efficiency increment of the co-sensitized DSSCs is in compliance with the increased ratio of BP-2/SQ2. The co-sensitized DSSC in which the ratio of BP-2 and SQ2 was 8:2 (v/v) exhibited a high efficiency of 8.14%. The TiO2 film adsorbed with co-sensitizers was subjected to Auger electron spectroscopy (AES) for probing the dye distribution across the TiO2 film depth. We synthesized benzothiadiazole (BT)-containing sensitizers with BT entity directly connected to 2-cyanoacrylic acid for DSSCs using ZnO as the photoanode aiming at better charge separation because of better electron transport. The cells performed better than those using TiO2 as the photoanode. The cell efficiency can be further improved when a newly developed brush hierarchical ZnO nanoplates were used as the light back scattering layer (SL) of the cell. Dyes consisting of 2,6-conjugated anthracene segment as the conjugated spacer, 9,10-bishexyloxyanthracen-phenylamino as the electron donor, and cyanoacrylic acid as the acceptor and anchor as well were synthesized. DSSCs using these sensitizers exhibited efficiencies 4.69&;#8722;7.52% under AM 1.5 illumination, and an impressively high efficiency (9.11%) surpassing the N719-based standard cell has also been achieved with the use of CDCA co-adsorbent. In order to enhance electron injection and dark current suppression, the dyes with two anchoring groups, D-π-(A)2, were synthesized from a 2,3,5-substituted thiophene motif. These dyes exhibit high molar extinction coefficient and good power conversion efficiency of the cells. With addition of co-adsorbent, CDCA, the device performance of all the DA-based DSSCs were improved by 1.03 to 2-fold, with the best efficiency reaching 95% of the N719-based standard cell (8.28%).