Roughness characterization of silver oxide anodes for use in efficient top-illuminated organic solar cells

In this study, we optimize the process of treating the surface of Ag anodes through exposure to UV–ozone, for the efficient planar heterojuction top-illuminated organic solar cells (OSCs). Several characteristics of Ag anodes such as work function (ФAnode), surface roughness (Ra) and sheet resistance are increased proportionally to exposure time following the formation of AgOx on the surface. Two factors, ФAnode and Ra, dominated the performance of the device due to their opposite contributions of power conversion efficiency (PCE). An increase in ФAnode flattened the energy barrier level between the anode and copper phthalocyanine, thereby benefiting hole injection and increasing open circuit voltage (VOC). An increase in Ra led to an increase in the density of localized traps, which obstructed hole injection and degraded the VOC. It also reduced reflectivity, thereby diminishing the short circuit current density (JSC). The top-illuminated OSCs in this study were optimized following surface treatment of the anode for 45 s to achieve a maximum PCE of 1.04%, VOC of 0.48 V, and JSC of 3.56 mA/cm2 with a fill factor of 60.7%.

Graphical abstractCharacteristics of Ag films treated by UV–ozone from 0 to 150 s such as work function, sheet resistance and reflectance spectra, surface morphological photos, roughness and average reflectance.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlightsEfficient top-illuminated organic solar cells use a low work function Ag anode.► AgOx formation increases work function and surface roughness of Ag anode. ► Work function and surface roughness dominate the performance of the device.