Electrode de-wetting as a failure mechanism in thermally-aged OPV devices

Organic photovoltaic (OPV) solar cells are a promising solar energy technology that could greatly increase the number of ways that solar cells can be utilised. Many of these applications involve the use of thin silver electrodes, however little attention has been paid to the role that electrode thickness plays in the operational stability of the device. This study found that inverted OPV devices with thin silver electrodes exhibited a catastrophic failure with only modest amounts of thermal ageing – primarily driven by substantial increases in the series resistance and decreases in the fill factor of the devices. Subsequent analysis by atomic force microscopy and Rutherford backscattering spectrometry showed that as the devices aged, gaps in thin silver electrodes appeared, showing that the electrode was de-wetting from the device, which would explain the rise in series resistance. This represents an intrinsic vulnerability in inverted OPV devices that can avoided if the silver electrode is sufficiently thick (> 60 nm). This problem can be overcome with the addition of a thin metal-oxide layer on top of the electrode which greatly slowed the electrode de-wetting with little variation in device performance – representing a potential solution for applications where a thin silver electrode is required.