A photoelectrochromic device based on gel electrolyte with a fast switching rate

Abstract A photoelectrochromic device (PECD), with no need for an external power source, is studied under open and short-circuit conditions with light illumination. In this report, the conductive polymer, poly(3,3-diethyl-3,4-dihydro-2H-thieno-[3,4- b ][1,4]dioxepine) (PProDOT-Et 2 ), plays two roles, namely, as the electrochromic thin layer for electrochrome and the counter electrode for dye-sensitized solar cell (DSSC). An organic photosensitive dye, FL dye1, is adsorbed on a TiO 2 electrode for providing the photocurrent. The electrolyte containing LiClO 4 , Br − /Br 3 − redox couple, succinonitrile, and poly-(vinylidenefluoride-hexafluoropropylene) (PVDF-HFP) dissolved in propylene carbonate (PC) is proposed as the gel electrolyte for the PECD. When the volume ratio of PVDF-HFP to succinonitrile is 6:2, the DSSC part provides a photocurrent density of 0.164 mA cm −2 , a photovoltage of 0.75 V, a fill factor of 0.48, with a solar-to-electric conversion efficiency of 0.059% to drive the electrochromic reaction. This solar-to-electric power is sufficient for observing the electrochromism of PProDOT-Et 2 , due to its high coloration efficiency. Moreover, when succinonitrile is added to the PVDF-HFP/PC electrolyte, the nucleus size of PVDF-HFP in the composite was reduced. This is because the effective space available for the primary nucleation in the composite was reduced, thus suppressing the crystallization and increasing the ionic conductivity and the diffusivity of the electrolyte. This results in a shorter bleaching time (20–35 s) of the PECD compared with the devices using succinonitrile (177 s) or PVDF-HFP (126 s) alone. In this case, the transmittance can be changed reversibly from 46% (bleached) to 15% (darkened) at 590 nm.