Performance analysis of different top metal electrodes in inverted polymer solar cells

In recent years, since the introduction of bulk heterojunction concept in an organic solar cell, the efficiency is increased to ∼6%. The benefits of bulk heterojunction (BHJ) organic solar cells are drawing interest for applications in next-generation solar cells. In this study, we analyze the optimal top electrode for practical polymer solar cells (PSC) fabrication by utilizing the optical properties of the electrode material and study their performance of PSC devices. The high work function metal electrodes having enhanced optical properties such as aluminum (Al), silver (Ag) and gold (Au) are considered in fabricating inverted PSC devices. It comprises of a blended polymer of poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM). Among the key photovoltaic parameters, the open circuit voltages (Voc) were strongly affected by the optical properties of the top electrode. From the experimental evidence, the increase in Voc of the Al and Ag electrode devices were found to be approximately 11.32% and 26.42% respectively. These values were significantly higher when compared to the Au electrode, as the parasitic absorption of incident photons were below 600 nm. Ag electrodes have excellent stability to ambient exposure which is comparable to Au. These investigations directed to conclude that, Ag is the optimal top electrode material for use in inverted devices. Also, in this study we investigated the incorporation of monodispersed ZnO as an n-type buffer layer to effectively transport electrons from active layer to the cathode electrode.