Determining the Effect of Different Heat Treatments on the Electrical and Morphological Characteristics of Polymer Solar Cells

Abstract

The device characteristics of polymer solar cells can be improved through an annealing process. This is especially true of the carrier mobility and the light absorption of P3HT:PCBM, which improves considerably after the annealing process. In the standard structure using indium-tin-oxide (ITO) as an anode, most studies have focused on the post-annealing process, where thermal annealing is performed after device fabrication. This work reports the effects of different annealing methods for inverted polymer solar cells, using ITO as a cathode. Similar levels of light absorption and P3HT crystallinity were obtained regardless of the annealing procedure in the inverted structure. However, compared with the post-annealed device, the pre-annealed device, which was thermally annealed after deposition of the P3HT:PCBM film, exhibited better charge extraction, owing to the superior device resistances and larger MoO3 grain size. Therefore, the pre-annealing method yields better performance than the post-annealing method.