Effect of organic solar cells using various sheet resistances of indium tin oxide and different cathodes: Aluminum, silver

The effect of different electrodes on organic solar cells (OSCs) performance was studied. Various sheet resistances of indium tin oxide (ITO) were used as an anode to find out which is suitable for OSCs application. The efficiency of OSCs based on small molecule material using different ITO substrates is almost the same due to the low absorption efficiency of active layer. In contrast, the efficiency of device based on polymer material using ITO (15 Ω/sq) has a better efficiency, which is attributed to reaching the optimal balance between the light transmittance and the carrier extraction. In cathode, the commonly used for OSCs are aluminum (Al) and silver (Ag), respectively. When substituting Ag for Al as a cathode, the efficiency of device based on copper phthalocyanine and C₆₀ increased from 0.71% to 0.86% and the efficiency of device based on boron subphthalocyanine chloride and C₆₀ increased from 2.61% to 2.96%. The performance enhancement is mainly ascribed to the current density (J_sc) improvement which is resulted from the difference of optical characteristic between the Al and Ag. The reflectance of Ag is higher than that of Al above wavelength of 405 nm, indicating that the light reflected from the Ag is more than that of Al. As a result, the more light can be absorbed in the active layer, leading to the efficiency of device using Ag as a cathode have above 10% improvement. However, the most commonly used cathode in OSCs is Al rather than Ag, which is also investigated.