In this work, the use of cobalt redox electrolytes in partly covered photoelectrochromic devices is investigated experimentally for the first time. The fabricated devices consist of a conductive glass photoanode coated with an electrochromic WO3 film of optical quality, including a mesoporous TiO2 layer (sensitized by the MK2 organic dye) that covers 20% of the device area. The liquid electrolyte is composed of 0.22 M Co(II)(bpy)3(PF6)2, 0.5 M LiClO4 and 0.5 M 4-tert-butylpyridine. A platinized conductive glass cathode completes the cell set-up. The fabricated devices are almost transparent in the bleached state with a Tlum value above 50%. They exhibit coloration speeds in the order of minutes, with a maximum contrast ratio of 2.9:1 after 21 min of illumination at 1000 W m−2 under open circuit conditions (OC), and high reversibility to fully bleached state in short circuit conditions. They provide a maximum measured power conversion efficiency of 0.28% due to limitations imposed by conflicting requirements of the photovoltaic and electrochromic elements, which is nonetheless sufficient to drive the coloration process. Since only the reduced specie Co2+ is present, initial illumination under OC for 3 min at 1000 W m−2 is necessary, prior to measurements, to oxidize Co2+ to Co3+ through the dye regeneration process in the electrolyte. The higher recombination losses of the Co2+/3+ redox shuttle compared to I−/I3−, which lead to a considerable reduction in coloration depth 20 days post fabrication due to loss of photoelectrons at the WO3/electrolyte interface, are suppressed by the use of a 35 nm thick ZnS barrier deposited on top of WO3. Remarkably, it results in a stabilized contrast ratio of 1.5:1, 23 days post fabrication. In addition, the color coordinates of the present devices resemble those of typical electrochromics: they exhibit blue coloration, as a result of the lack of the absorbing iodine in the electrolyte that produces a green tint.

Photoelectrochromic devices with cobalt redox electrolytes / Dokouzis, A.; Bella, F.; Theodosiou, K.; Gerbaldi, C.; Leftheriotis, G.. - In: MATERIALS TODAY ENERGY. - ISSN 2468-6069. - ELETTRONICO. - 15:(2020), pp. 100365-1-100365-8. [10.1016/j.mtener.2019.100365]

Photoelectrochromic devices with cobalt redox electrolytes

F. Bella;C. Gerbaldi;
2020

Abstract

In this work, the use of cobalt redox electrolytes in partly covered photoelectrochromic devices is investigated experimentally for the first time. The fabricated devices consist of a conductive glass photoanode coated with an electrochromic WO3 film of optical quality, including a mesoporous TiO2 layer (sensitized by the MK2 organic dye) that covers 20% of the device area. The liquid electrolyte is composed of 0.22 M Co(II)(bpy)3(PF6)2, 0.5 M LiClO4 and 0.5 M 4-tert-butylpyridine. A platinized conductive glass cathode completes the cell set-up. The fabricated devices are almost transparent in the bleached state with a Tlum value above 50%. They exhibit coloration speeds in the order of minutes, with a maximum contrast ratio of 2.9:1 after 21 min of illumination at 1000 W m−2 under open circuit conditions (OC), and high reversibility to fully bleached state in short circuit conditions. They provide a maximum measured power conversion efficiency of 0.28% due to limitations imposed by conflicting requirements of the photovoltaic and electrochromic elements, which is nonetheless sufficient to drive the coloration process. Since only the reduced specie Co2+ is present, initial illumination under OC for 3 min at 1000 W m−2 is necessary, prior to measurements, to oxidize Co2+ to Co3+ through the dye regeneration process in the electrolyte. The higher recombination losses of the Co2+/3+ redox shuttle compared to I−/I3−, which lead to a considerable reduction in coloration depth 20 days post fabrication due to loss of photoelectrons at the WO3/electrolyte interface, are suppressed by the use of a 35 nm thick ZnS barrier deposited on top of WO3. Remarkably, it results in a stabilized contrast ratio of 1.5:1, 23 days post fabrication. In addition, the color coordinates of the present devices resemble those of typical electrochromics: they exhibit blue coloration, as a result of the lack of the absorbing iodine in the electrolyte that produces a green tint.
File in questo prodotto:
File Dimensione Formato  
311) A. Dokouzis et al., Mater. Today Energy 15 (2020) art. no. 100365.pdf

non disponibili

Tipologia: 2a Post-print versione editoriale / Version of Record
Licenza: Non Pubblico - Accesso privato/ristretto
Dimensione 1.87 MB
Formato Adobe PDF
1.87 MB Adobe PDF   Visualizza/Apri   Richiedi una copia
MTENER_2019_127_R1.pdf

accesso aperto

Tipologia: 2. Post-print / Author's Accepted Manuscript
Licenza: Creative commons
Dimensione 3.3 MB
Formato Adobe PDF
3.3 MB Adobe PDF Visualizza/Apri
Pubblicazioni consigliate

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11583/2802019