We present the effects of a concentration graded Li:Al cathode when it is made by one-step evaporation method using single alloy sources on the performance of organic solar cells. The concentration profile of the Li:Al cathode and related interface energy levels were investigated by means of secondary ion mass spectroscopy and ultraviolet photoelectron spectroscopy, in comparison with those of a common Al cathode. The results indicate that interfacial lithium accumulation introduces a cascade decrease of the work function (WF) of the cathode. The WF graded cathode applied to bulk heterojunction solar cells resulted in increased short circuit current and power conversion efficiency. Furthermore, the Li:Al cathode avoids the formation of interface AlC complex, which may cause disruption of electron transport.
Bibliographical noteFunding Information:
This research was supported by a WCU Grant (R32-2008-000-10142-0) and ERC Program ( R11-2007-045-01002-0(2009 )) from MEST. J. H. Park acknowledges Research Programs through the NRF Grant funded by MEST ( 2011-0006268 and Future-based Technology Development Program (Nano Fields) ( 2010-0029321 )).
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films