Photovoltaic action spectra of metal–phthalocyanine Schottky barrier cells

Abstract

We have measured the direct current (dc) action spectra of Al and In/phthalocyanine (α, β, and x-H2Pc and VOPc) photovoltaic cells in the wavelength range 400–900 nm. The data were analyzed in terms of both the local carrier generation and exciton diffusion models. According to the local carrier generation model, photoactive barrier widths w of 390, 475, 310, and 950 Å for In/α, β, x-H2Pc, and VOPc, respectively, were obtained. The depletion region width of In–phthalocyanine Schottky junctions were independently measured using a dc discharge capacitance technique. In all cases, the depletion region widths (capacitance) were consistently smaller than the photoactive collection region widths (action spectra). These results suggest that excitons produced within a diffusion length of the barrier can diffuse into the barrier zone and dissociate into collectable carriers. Using a combined local carrier generation and exciton diffusion model, a barrier width of the order of 200–300 Å and an exciton diffusion length of 300–500 Å was estimated for In/x-H2Pc cells.