Influence of the Coordinated Ligand on the Optical and Electrical Properties in Titanium Phthalocyanine-Based Active Films for Photovoltaics

Tetravalent titanyl phthalocyanine (TiOPc) and titanium phthalocyanine dichloride (TiCl₂Pc) films were deposited via the high-vacuum thermal evaporation technique and subsequently structurally and morphologically characterized, to be later evaluated in terms of their optoelectronic behavior. The IR and UV-vis spectroscopy of the films displayed α- and β-phase signals in TiOPc and TiCl₂Pc. Additionally, the UV-vis spectra displayed the B and Q bands in the near-UV region of 270–390 nm and in the visible region between 600 and 880 nm, respectively. The films presented the onset gap (~1.30 eV) and the optical gap (~2.85 eV). Photoluminescence emission bands at 400–600 nm and 800–950 nm are present for the films. One-layer ITO/TiCl₂Pc or TiOPc/Ag and two-layer ITO/PEDOT:PSS/TiCl₂Pc or TiOPc/Ag planar heterojunction devices with poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) deposited by the spin-coating technique were constructed. In these devices, an electrical activation energy between 0.18 and 0.21 eV and a refractive index between 1.14 and 1.44 were obtained. The devices presented a change in the J–V curves for the illuminated and darkness conditions, as much as 1.5 × 10² A/cm², related to the device architecture and phthalocyanine ligand. The latter indicates that the films should be used for optoelectronic applications.