Stable polymer solar cells using conjugated polymer as solvent barrier for organic electron transport layer

Abstract

Redissolusion of an organic film by the subsequent processing solvent is a critical issue for the fabrication of organic multilayer structures and this can limit the advanced development of organic devices for flexible/stretchable application. In this study, we present a simple, doable, and straightforward approach to overcome this problem through introducing a solvent barrier. As a demonstration, we have successfully deposited an organic photoactive material on top of an organic electron transport layer (ETL) by pre-depositing a solvent barrier layer on the ETL for fabricating inverted polymer solar cells (PSCs). Water-/alcohol-soluble and thermally cross-linkable poly[9,9-bis(6’-(N,N-diethylamino)propyl)-fluorene-alt-9,9-bis-(3-ethyl(oxetane-3-ethyloxy)-hexyl)-fluorene] (PFN-OX) is selected as the solvent barrier material. PSCs fabricated with organic-ETL/PFN-OX bilayer show improved performance in comparison with those using conventional ZnO as ETL due to the enhanced interface compatibility as well as improved charge extraction, hole blocking, and interfacial recombination properties. In addition, those devices also exhibit longer lifetime and better light-soaking stability. Therefore, the approach of introducing solvent barrier is facile to stack organic films of similar solvent preference together and the resulting structure carries enhanced interfacial electrical properties, which can have positive effects on the device performance. We believe that our proposed idea is very useful and can advance the development of flexible/stretchable devices to be applied in wearable technology.