Facilitating electron collection of organic photovoltaics by passivating trap states and tailoring work function

Abstract

The low-temperature solution-processed ZnO normally has intrinsic oxygen vacancies and various surface defects such as organic residues and surface adsorbates. When ZnO film is used in organic solar cells as electron selective layer, these defects will serve as bimolecular recombination centers for light induced charge carriers and trap electrons, leading to an unsatisfied device performance. Herein, we demonstrate an effective way to employ a simple combination of UV-ozone (UVO) and dipole treatment to passivate the ZnO layer, and the electronic property of ZnO layer is great improved upon eliminating the residual hydrocarbons and passivating surface traps. The reengineered uniform ZnO films play a major role on the facilitated charge transfer and decreased contact resistance, resulting in an enhanced device efficiency. The optimized ZnO transport layer also regulates the upper active layer depositing and morphology, and consequently increases the dissociation of photo-excitons and suppresses charge recombination.