Interfacial processes in small molecule organic solar cells

This paper presents an overview of the recent progress of small molecule organic solar cells mainly based on the previous works of our group. We will mainly focus on the interfacial processes in the cells. The dissociation of excitons at electrode/organic and organic/organic interfaces can be directly observed by transient photovoltage measurements. A simple model including dissociation of excitons at the interface and drift of free carriers in the built-in field is proposed to explain the observed signals of transient photovoltage. Besides exciton-blocking and preventing damage due to cathode evaporation, blocking permeation of oxygen and/or water molecules and modulating the built-in field are proposed as functions of the buffer layer between C60 and Al. By the use of the inverted structure, a shelf lifetime of over 1500 h is achieved for unencapsulated small-molecule organic solar cells.