Photovoltaic and rectification properties of Al/Mg phthalocyanine/Ag Schottky-barrier cells

Abstract

The photovoltaic and rectification properties of Al/Mg phthalocyanine/Ag sandwich cells are reported. At low voltages, the current in the forward direction varies exponentially with voltage. A charge density of [inverted lazy s]1018/cm3 is estimated from C-V measurements. The short-circuit photocurrent JscαFm (m [inverted lazy s]0.5), where F is the incident light intensity. The open-circuit photovoltage Vocα logF as expected for a Schottky barrier or p-n junction. The J-V curve in the photovoltaic mode is characteristic of a cell with large series resistance. From the photovoltaic action spectra, the electron diffusion length is estimated to be [inverted lazy s]1.5×10−6 cm. The action spectrum is dependent on the direction of the incident radiation. A theory is presented which explains the results. The junction is attributed to a Schottky barrier of Vd ∼ 0.6 eV and width ∼ 2.5 × 10−6 cm estimated from C-V measurement. The values determined from photovoltaic measurements are in agreement. The lifetime of electrons is estimated to be ∼ 10−9 sec and the mobility ∼ 0.1 cm2 /V sec. The quantum efficiency for carrier generation is ∼ 1.5 × 10−3. At 690 nm, with light incident on the Al side, the photovoltaic efficiency is about 0.01%, one of the highest ever reported for organic photovoltaic cells.