The role of solvent and morphology on miscibility of methanofullerene and poly(3-hexylthiophene)

• Published in: Thin solid films Vol. 520; no. 16; pp. 5466 - 5471
• Main Authors: Gadisa, Abay, Tumbleston, John R., Ko, Doo-Hyun, Aryal, Mukti, Lopez, Rene, Samulski, Edward T.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.06.2012; Elsevier
• Subjects: Applied sciences; Chemical interdiffusion; diffusion barriers; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Diffusion in solids; Energy; Exact sciences and technology; Fullerenes and related materials; diamonds, graphite; Interdiffusion; Materials science; Miscibility; Morphology; Natural energy; P3HT/PCBM bilayer; Photovoltaic; Photovoltaic conversion; Physics; Poly(3-hexylthiophene); Solar cells. Photoelectrochemical cells; Solar energy; Specific materials; Transport properties of condensed matter (nonelectronic); Miscibility; Poly(3-hexylthiophene); Interdiffusion; Photovoltaic; Morphology; P3HT/PCBM bilayer; Organic polymers; Thin film; Photovoltaic cell; Solar cell; Casting; Thiophene derivative polymer; Phase separation; Fullerenes; Butyric derivative polymer; Overlayers; Interface; Bilayers; Heterojunction
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2012.03.117

A bicontinuous, percolating bulk heterojunction morphology is integral to organic polymer solar cells. Understanding the factors affecting the miscibility of photovoltaic polymers with a fullerene electron acceptor molecule is a key to controlling the morphology. Starting from discreet pure phases – a poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) bilayer film – the evolution of the P3HT–PCBM interface was studied with particular attention to the role of residual solvent in P3HT on PCBM interdiffusion. This investigation shows that in the bilayer geometry PCBM can rapidly diffuse into amorphous P3HT, but phase separation is maintained if the P3HT layer is cast from a very volatile solvent or if it is annealed prior to casting the PCBM overlayer to complete the bilayer geometry. ► We examine miscibility of P3HT with a fullerene molecule PCBM. ► Amorphous polymer morphology enhances interdiffusion. ► Annealed bilayer is subjected to large phase-separation if PCBM is cast on dry P3HT. ► Phase-separated PCBM clusters extend throughout the bilayer film.