Investigation on the Performance of an Organic Solar Cell by the Modification of Cathode with Lanthanum Fluoride Thin Layer

Abstract

Performance of organic solar cell (OSC) using the modification of cathode has been investigated in this research. OSC has been fabricated using the blend of P3HT (poly (3-hexylthiophene)) and PCBM (Phenyl C61 butyric acid methylester) at 1:1 ratio. E-beam evaporated indium tin oxide (ITO) has been used as the anode. A novel bi-layer of e-beam-evaporated LaF₃ and Al (LaF₃/Al) has been used as the cathode. The morphology of the ITO, P3HT: PCBM and LaF₃ layer has been investigated by Atomic Force Microscope (AFM). LaF₃ layer between P3HT: PCBM and Al layer was found to influence the reverse current, open-circuit voltage and efficiency of OSC. Various thicknesses of LaF₃ layer have been investigated, and 3nm thick LaF₃ layer was found to be the optimum thickness for the enhancement of the various solar-cell parameters of our fabricated OSC. The effect of annealing on the performance of the cell has been also investigated. The post-fabrication annealed devices, with or without the LaF₃ layer, exhibited higher values of short-circuit current, open-circuit voltage than those of similar devices annealed before depositing the Al metal. It was found that annealing at 150°C for 20 minutes provided the best result. The overall power conversion efficiency was found to enhance several times than that of the conventional structure of OSC having only Al as the cathode. Altogether the experimental results show that bi-layer of LaF₃/Al cathode could enhance the overall performance of OSC.