Investigation of p-dopant diffusion in polymer films and bulk heterojunctions: Stable spatially-confined doping for all-solution processed solar cells

The spatial stability of the soluble p-dopant molybdenum tris[1-(methoxycarbonyl)-2-(trifluoromethyl)-ethane-1,2-dithiolene] in polymer and polymer blend films is investigated via secondary ion mass spectrometry and current-voltage measurements. Bi-layer and tri-layer model structures, P3HT/doped P3HT and P3HT:ICBA/doped P3HT/P3HT:ICBA respectively, are fabricated using soft-contact transfer lamination to study the diffusion of the dopant. While the dopant is very mobile in pure P3HT, it is far more stable at the interface with the P3HT:ICBA bulk heterojunction. Our findings suggest a promising route to achieve spatially-confined doping with long-term stability, leading to hole-collection/injection contacts for all-solution processed polymer devices.