Near-infrared absorbing unsymmetrical Zn(II) phthalocyanine for dye-sensitized solar cells

• Published in: Inorganica Chimica Acta Vol. 407; pp. 289 - 296
• Main Authors: Singh, Varun Kumar, Salvatori, Paolo, Amat, Anna, Agrawal, Saurabh, De Angelis, Filippo, Nazeeruddin, Md.K., Krishna, Narra Vamsi, Giribabu, Lingamallu
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.10.2013
• Subjects: Dye-sensitized solar cells; Phthalocyanine; Redox electrolyte; Spectroelectrochemal; Unsymmetrical phthalocyanine; Phthalocyanine; Dye-sensitized solar cells; Spectroelectrochemal; Unsymmetrical phthalocyanine; Redox electrolyte
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/j.ica.2013.07.052

A new unsymmetrical Zinc(II) phthalocyanine has been designed and synthesized based on ‘push–pull’ concept for dye-sensitized solar cell application. The unsymmetrical phthalocyanine is having six S-aryl groups at non-peripheral positions, which acts as electron releasing (‘push’) and a carboxyl group at peripheral position, which act as electron withdrawing (‘pull’) of phthalocyanine. The new unsymmetrical phthalocyanine was tested in DSC using liquid redox electrolyte. •Unsymmetrical Zn(II) phthalocyanine based on ‘push–pull’ concept.•Absorption shifted to N-IR regions.•HOMO–LUMO level matched with TiO2 conduction band as well as I−/I3− redox couple. Unsymmetrical Zn phthalocyanine consisting of six S-aryl groups at α-positions and a carboxy anchoring group at β-position has been designed and synthesized for dye-sensitized solar cells (DSCs) applications. The unsymmetrical phthalocyanine has been characterized by elemental, MALDI-MS, IR, 1H NMR, UV–Vis, fluorescence (steady-state & lifetime) and electrochemical (including spectroelectrochemical) methods. The Q-band absorption maxima of the unsymmetrical phthalocyanine was red-shifted due to the presence of S-aryl groups, which destabilizes the HOMO level consistent with electrochemical and in situ spectroelectrochemical studies. The redox processes are assigned to the macrocyclic ring-based electron transfer processes, the LUMO of the unsymmetrical phthalocyanines lies above the TiO2 conduction band, and the HOMO is well below the potential of the I−/I3− redox electrolyte. The experimental results are supported by DFT/TD-DFT studies. The new unsymmetrical phthalocyanines was tested in DSCs using I−/I3− redox electrolyte system.