Pentacene homojunctions: Electron and hole transport properties and related photovoltaic responses

We report on organic $p\text{\ensuremath{-}}i\text{\ensuremath{-}}n$ homojunctions composed of differently doped vacuum-deposited pentacene layers. We observe a remarkably high built-in voltage of 1.65 V. An analysis of the current-voltage characteristics under dark and illuminated conditions reveals that the open-circuit voltage is directly related to the built-in voltage and that the recombination process is influenced by the distinct charge transport properties of electrons and holes in the pentacene film. By a comparison with $p\text{\ensuremath{-}}i\text{\ensuremath{-}}p$ and $n\text{\ensuremath{-}}i\text{\ensuremath{-}}n$ single-carrier homojunctions, deep trap states located around 0.63 eV below the electron transport level are shown to influence the properties.