The effect of the central ligand on the surface photovoltage of phthalocyanine films

Abstract

The photovoltage at light intensity saturation, and the relaxation time associated with this photovoltage have been measured for a variety of phthalocyanine (Pc) thin films and the results are: H2Pc(10.60 mV, 25.3 msec), NiPc(10.99 mV, 43.2 msec), CuPc(5.24 mV, 47.2 msec), and ZnPc(0.01 mV, 18.4 msec). No observable photovoltage signal was obtained for either FePc or CoPc. The spectral dependence of the photovoltage signals for these phthalocyanine dyes is related to their optical absorption spectra. Efforts have been made in the literature to connect the semiconducting properties of these organic dyes to the differing luminescent, magnetic, and optical properties of the various phthalocyanines. This work indicates that the size of the photovoltage signal is unrelated to any of these parameters. The size of the photovoltage is, however, closely correlated with the alignment of the energies of the d orbitals on the central metal ligand with the valence band molecular orbital of the outer phthalocyanine ring, as determined from photoemission measurements.

Surface photovoltage phenomena: theory, experiment, and applications

“…In order to apply such an approach to SPS data, it is important to consider how well SPV spectra are expected to resemble absorption spectra. Detailed experimental comparisons between SPV and absorption spectra reveal that the two are often similar, but never identical [102,409,410]. Let us consider the sources of this discrepancy: ®rst, the SPV is proportional to the excess carrier density only for a low enough injection of excess carriers, n (see Eq.…”

“…Sign reversals of the same feature should therefore be treated with caution. Distinction between surface and bulk states has also been performed by means of treating the bulk, e.g., by changing the bulk dopant [296,340,351,395], or sample fabrication procedures [305,333,393,409].…”

Photoélectrochimie des phtalocyanines sans métal, de cuivre et de fer

“…Ces dopants agissent cornme pikges h Clectrons, entrainant la creation d'un plus grand nombre de trous mobiles. ~t a n t donnC que les phtalocyanines absorbent fortement dans la region visible du spectre solaire, avec une bande interdite de l'ordre de 1,8-2,l eV (3), il a CtC suggere de les utiliser dans des cellules photovoltai'ques (9)(10)(11)(12)(13)(14)(15)(16). Bien que le rendement de conversion de 1'Cnergie solaire en Cnergie Clectrique soit trks faible (< 1 %), a cause principalement du faible rendernent quantique, certaines phtalocyanines (H,Pc, CuPc, NiPc, MgPc) ont manifest6 des activitCs intkressantes.…”

[5]Helicene-Fused Phthalocyanine Derivatives. New Members of the Phthalocyanine Family

“…Organic materials with linear optical absorptions in the near-IR to far-red (700−1500 nm) region have the potential for numerous applications, such as IR sensing and display devices. − Phthalocyanine (Pc) derivatives, by virtue of their unique highly delocalized cyclic π-electron system, absorb strongly in the near-IR region and exhibit a number of outstanding physical properties, such as semiconductive, , nonlinear optical, , electrochromic, photovoltaic, − liquid crystalline, , and catalytic , properties. These properties offer a wide range of applications, namely, electrooptical devices (e.g., optical limiter), electronic sensors, optical data storage, , electrochromic displays for laser address storage systems, and heterogeneous catalysis …”