Anomalous photovoltaic behavior under illumination of γ - In2Se3 nanostructures used as hole transport layer in organic solar cell

Abstract

Indium selenide is currently receiving tremendous attention in device application and studies related to two dimensional nanostructured technologies. Non-layered γ-In2Se3, which is a stable phase at room temperature, was successfully synthesized in oleylamine after 10 min at 240 °C from InCl3 and elemental selenium. Prolonged reaction time resulted in structural transformation thereby producing layered nanostructures and mixed phases and stoichiometries. X-ray diffraction patterns and Raman studies confirmed that the nanostructures synthesized were predominantly γ-In2Se3. Absorption and photoluminescence studies established the existence of trap levels 1.52 eV, 1.94 eV, 2.30 eV and 2.9 eV situated above the valence band possibly due to defects from cationic vacancies. Negative photoconductivity and negative shift on the open circuit potential (Voc) were exhibited in organic bulk heterojunction solar cell device when γ-In2Se3 was used as hole transport layer. Under illumination, the short circuit current density (Jsc) dropped below the dark current. This decrease in Jsc was observed to increase with increasing light intensity. The trap levels captured the conduction band electrons, aided in the destruction of minority carriers and enhanced recombination thus resulting in the NPC and the negative shift in the Voc exhibited by the device.