On the Optimization of Fast-Response Photoelectrochromic Device Containing Gel Electrolytes
Date Issued
2010
Date
2010
Author(s)
Wu, Chia-Hui
Abstract
In this thesis, the optimization of a photoelectrochromic device (PECD) toward its electro-optical performance is discussed. This system is comprised of a poly(thiophene) derivative conducting polymer, poly(3,3,-diethyl-3,4-dihydro-2H-thieno-[3,4-b][1,4]dioxepine)(PProDOT-Et2) as the electrochromic layer, in conjuction with gel-type electrolytes.
At first, the optical performances of PECDs are comparred using the electrolyte based on succinonitrile (Electrolyte S) and poly-(vinylidene fluoridehexa- fluoropropylene) (PVDF-HFP) (Electrolyte P). Under the light illumination and short-circuit condition for darkening the device, the devices using either electrolyte spend ca. 3s for darkening and the transmittance attenuation (ΔT) is 40%. At open-circuit condition for bleaching the device, the device using Electrolyte S exhibits the bleaching time of ca. 3 min and the other one using Electrolyte P is ca. 2 min. The difference results from crystallinity degree of the electrolyte, and resulting in difference of the ionic mobility. Thus, the relationship between the crystallinity degree of the electrolyte and the response time of the device is discussed. It is found that the crystallinity degree can be suppressed by mixing the Electrolyte P and Electrolyte S. The ionic conductivity and diffusion coefficient are increased with the decreasing of crystallinity degree. So the response time of the PECD can be improved, i.e. the bleaching time is shortened to ca. 20 s.
Afterward, the electro-optical performance of the PECD is attempted to improve by combining the electrochromic material, PProDOT-Et2, with Pt. We sputtered the Pt in between the interface of PProDOT-Et2 and electrolyte (electrolyte/Pt/PProDOT-Et2/conducting substrate) and in between the interface of PProDOT-Et2 and conducting substrate (electrolyte/PProDOT-Et2/ Pt/conducting substrate), respectively, to prepare the electrochromic layer in the PECD. According to the I-V characteristic of the device, the later configuration ,compared with the former, that sputters a small amount of Pt on conducting glass before the deposition of PProDOT-Et2 shows better power output result (Voc = 0.81 V, Jsc = 0.255 mA/cm2, and conversion efficiency ＝0.095%). Furthermore, it is also verified from the Scanning Electrochemical microscopy, SECM, that the later electrode provides higher electron transfer rate constant.
In the last part, Br2 is added into the gel electrolyte to form Br3- ions by reacting with Br- ions, which is attempted to improve the optical response and the power output performance of the PECD. It is evidenced from the analysis of SECM that the redox reaction is occurred between the Br-/ Br3- ions and the PProDOT-Et2 conducting polymer without applying any voltage. The optical response of the PProDOT-Et2 electrochromic material is thus changed. By changing the addition amount of Br2, the optimal concentration is found at 1.0 mM Br2. It is because that the redox reaction between the redox couple and the PProDOT-Et2 approaches to equilibrium. After the optimization of this device system, the transmittance attenuation and the bleaching time is ca. 32% and ca. 30 s, respectively. This device can also supply power output with Voc = 0.74 V, Jsc = 0.339 mA/cm2, and conversion efficiency＝0.122%.
Subjects
crystallinity
gel electrolyte
photoelectrochromic device
response time
scanning electrochemical microscopy.
Type
thesis
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