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Development of Highly Efficient and Durable Dye-sensitized Solar Cell

Development of Highly Efficient and Durable Dye-sensitized Solar Cell
Other Titles
염료감응 태양전지의 고효율화 및 장기성능 향상을 위한 연구
Alternative Author(s)
Kyung Chul Sun
Issue Date
In this thesis, to enhance the power conversion efficiency (PCE) of dye-sensitized solar cells (DSSCs) and to overcome the problems associated with the use of liquid electrolyte in a DSSC, advance materials and their processing is proposed which is followed by the importance of the Titanium dioxide (TiO2) nanotubes (TNT) and their application in DSSC based on fibrous membrane electrolyte. First, pure anatase TNT were synthesized by hydrothermal method using commercial, low cost titanium material (P25) due to which manufacturing cost of DSSC was enormously reduced. To enhance the PCE of DSSC, a new type of double layered photoanode was prepared and optimized by using TiO2 nanoparticle as main layer and TNT as over-layer. These Prepared cells were analyzed by optical, photovoltaic and electrochemical measurement systems. The cells having TNT over-layer showed longer electron life time, higher surface area, pore volume and improved light harvesting efficiency. Second, a novel strategy was adopted to improve the performance of DSSC with better absorption of solar spectrum both in the visible as well as near IR regions. Composite over-layer structure of 75/25-TNT/P25 showed best photovoltaic performance. Different characterization analysis proved that optimizes DSSC with composite over-layer structure have significant advantages of better dye adsorption, large surface area, better photo-electron generation, better conductive behavior, superior electron recombination restraint characteristics, better light scattering, and long electron lifetime. Third, in order to overcome the problems associated with the use of liquid electrolyte in DSSCs having carbon based counter electrode, PVdF-co-HFP based fibrous electrospun membrane electrolyte was prepared and compared with liquid and polymer-gel based electrolytes with various DSSC structures. In this work, SMT (7+4 ㎛) photoanodes were used due to the possibility of getting minimum thickness of membrane, thickness of carbon counter electrode, and processing of cell assembly. To understand their surface and interface kinetics and mechanism, electrochemical equivalent circuits were applied and analyzed by the simulation. As a result, under the carbon based counter electrodes in DSSCs, fibrous membrane electrolyte show positive effect for PCE compared to polymer electrolyte due to their contact between electrode and electrolyte. Lastly, polyethylene terephthalate (PET) was used in the form of a wet-laid nonwoven as a matrix for an electrolyte in DSSC. Due to the thickness of fibrous membrane, and processing of assembly of the DSSC, DMT (14+4 ㎛) photoanodes were prepared. This fibrous membrane can better absorb electrolyte turning into a quasi-solid, providing excellent interfacial contact between both electrodes of the DSSC and preventing a short circuit. An optimized membrane provides better and more desirable structure for ionic conductivity, resulting in the improvement of the photovoltaic performance after calendering. With the aim of increasing the absorbance, the membrane was plasma-treated with argon and oxygen separately, which resulted in retention of the electrolyte, avoiding its evaporation, and a 15 % longer lifetime of the DSSC compared to liquid electrolyte. Proposed materials in this thesis are promising based on innovative approach for further improving the performance of DSSC and this will be a concrete fundamental background towards the development of the applications of the next generation solar cells including highly efficient and flexible solar cells. Furthermore, these materials can also contribute progress of chemical cells such as battery and fuel cells.
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