Photovoltaic properties of metal-free phthalocyanines. I. Al/H2Pc Schottky barrier solar cells

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Abstract
The photovoltaic properties of Schottky barier solar cells, made by dispersing particles of the x form of mental‐free phthalocyanine in a binder polymer and sandwiching between NESA (SnO2/Sb) and aluminum electrodes, have been studied. A power conversion efficiency of over 6% for transmitted light at low power densities (0.06 W/m2) has been obtained for monochromatic irradiation at 670 nm. At peak solar power density (1400 W/m2) the extrapolated power conversion efficiency (η) for transmitted 670 nm irradiation decreases to 0.01%. The decrease in η with intensity was attributed to a space charge limitation due to nonlinear resistance. The devices exhibit Voc’s as high as 1.1 V, but are still limited by a field dependent quantum efficiency. Analysis of the action spectra of these devices revealed the formation of a thin photoactive depletion region (∼400 Å) at the semiconductor/metal interface. These devices are capable of capturing 30% of the solar spectrum within the photoactive region. The effect of pigment loading, cell thickness, light intensity, binder materials, doping and dye sensitization has been studied. Based upon sunlight absorption, theoretical efficiencies for these devices appear high.