Charge formation and transport in bulk-heterojunction solar cells based on alternating polyfluorene copolymers blended with fullerenes

• Published in: Organic electronics Vol. 7; no. 4; pp. 235 - 242
• Main Authors: Jespersen, Kim G., Zhang, Fengling, Gadisa, Abay, Sundström, Villy, Yartsev, Arkady, Inganäs, Olle
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 2006; Elsevier
• Subjects: Applied sciences; Atom and Molecular Physics and Optics; Atom- och molekylfysik och optik; Bulk-heterojunction solar cells; Charge transport; Electronics; Exact sciences and technology; Fysik; NATURAL SCIENCES; NATURVETENSKAP; Optoelectronic devices; Physical Sciences; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Transient absorption spectroscopy; Bulk-heterojunction solar cells; 78.47.+p; Charge transport; 73.61.ph; 73.50.Pz; Transient absorption spectroscopy; Solar cell; Transport process; Conjugated polymer; Absorption spectrometry; 73.50.Pz; 73.61.ph; 78.47.+p; Fullerenes; Charge carrier generation; Transient absorption spectroscopy; Charge transport; Bulk-heterojunction solar cells; Heterojunction
• ISSN: 1566-1199; 1878-5530; 1878-5530
• DOI: 10.1016/j.orgel.2006.03.001

We investigate charge formation in bulk-heterojunction solar cells based on conjugated polymers in the form of alternating polyfluorene copolymers and the methanofullerene PCBM. Using transient absorption spectroscopy we show that optimal charge formation is obtained with 20–50
wt% PCBM. This is in contrast to the maximum short circuit current density obtained at ∼80
wt% PCBM as determined by steady state current density–voltage characterization. Hence, we show explicitly that the solar cell performance of these interpenetrating polymer networks containing PCBM is limited by charge transport rather than by formation of charges.