Organic Thin-Films by Wet-Processes for Flexible Bulk-Heterojunction Organic Solar Cells

In this work, poly(3, 4-ethylenedioxythiophene) blended to polystyrene sulfonate (PEDOT:PSS) and poly(3-hexylthiophene) composite with 1-(3-methoxycarbonyl)propyl-1-phenyl[6], [6]C61 (P3HT: PCBM) deposited by spin and blade coating were thoroughly investigated by optical, morphological, and structural characterization techniques targeting the improvement of organic solar cells (OSCs). Processing parameters as surface treatment, filtration, concentration, additives, and deposition speed were studied in order to optimize OSC performance. The hole transport layer by spin coating featured a thickness of ca. 50 nm, a roughness of 2 nm, and absorbance lower than 0.03. Deposition by blade coating reduced film thickness and roughness to approx. 20 nm and 1.5 nm, respectively. It also brought further down thin-film absorption in the visible spectrum. P3HT: PCBM thickness could be easily varied from 100 to 200 nm by both deposition techniques. Absorbance (maximum of 0.4) and XRD data demonstrated enhanced thin-film crystallinity for P3HT: PCBM spun from 26 mg/mL solutions. Semiconducting films by blade coating provided thicker films
${(> 140\ \text{nm})}$
and an even higher absorption (0.5 - 0.8) due to the p-type molecule. The next step is to integrate these films to flexible OSCs.