Thermal Annealing Study on P3HT:PCBM Based Bulk Heterojunction Organic Solar Cells Using Impedance Spectroscopy

摘要

Recently, Thermal annealing is an important process for bulk heterojunction organic solar cells (BHJ OSCs) to improve the device efficiency and performance of the organic solar cells. Here in, we have examined the changes in the efficiency and morphology of P3HT:PCBM film according to the thermal annealing temperature to find the changes during the annealing process by measuring the optical absorption, atomic force microscope and X-ray diffraction. We also investigated the effect of different annealing process conditions (without, pre- and post-annealing) on the device performance of the inverted bulk heterojunction organic solar cells consist the structure of ITO/ ZnO / P3HT:PCBM / MoO_3/ Al by measuring AC impedance characteristics. Particularly, the power conversion efficiency (PCE), crystalline nature of the polymer, light absorption and the surface smoothness of P3HT:PCBM films are significantly improved after the annealing process. These results indicated the improvement in terms of PCE, interface smoothness between the P3HT:PCBM and MoO_3 layers of the post annealed device originated from the decrease of series resistance between P3HT:PCBM layer and Al electrodes, which could be due to decrease in the effective life time of charge carriers.