Influence of thermal annealing on the deformation of a lithium fluoride nanolayer in polymer : fullerene solar cells

¹  Organic Nanoelectronics Laboratory, Department of Chemical Engineering, Kyungpook National University Daegu 702-701, Republic of Korea
²  Institute of Biomedical Engineering, Imperial College London - Exhibition Road, London SW7 2AZ, UK, EU

Corresponding authors: ykimm@knu.ac.kr y.kim@imperial.ac.uk

Received: 21 July 2008
Accepted: 28 October 2008

Abstract

In this letter we attempted to examine the possible deformation of a lithium fluoride (LiF) nanolayer inserted in between a light-absorbing polymeric layer (a mix of poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6) C₆₁ (PCBM)) and a metal (Al) electrode in polymer : fullerene solar cells. The direct annealing of devices with the LiF nanolayer resulted in a gradual decay in device performances with annealing time at an optimum temperature, after exhibiting a maximum efficiency by very short-time annealing (3 min). In contrast, the study of film annealing and post-deposition of the LiF nanolayer showed that a longer-time (120 min) annealing led to a maximum efficiency. These results indicate that the LiF nanolayer in devices is vulnerable to the deformation upon thermal annealing.