Cyclobutadiene-C60 Adducts: N-Type Materials for Organic Photovoltaic Cells with High Voc

Publication Type:

Journal Article

Source:

Adv. Funct. Mater., Wiley Online Library, Volume 23, Issue 24, p.3061-3069 (2013)

ISBN:

1616-301X

Keywords:

2013, 2013 and earlier

Abstract:

New tetraalkylcyclobutadiene–C60 adducts are developed via Diels–Alder cycloaddition of C60 with in situ generated cyclobutadienes. The cofacial
π-orbital interactions between the fullerene orbitals and the cyclobutene
are shown to decrease the electron affinity and thereby increase the
lowest unoccupied molecular orbital (LUMO) energy level of C60
significantly (ca. 100 and 300 meV for mono- and bisadducts,
respectively). These variations in LUMO levels of fullerene can be used to
generate higher open-circuit voltages (VOC) in bulk heterojunction polymer
solar cells. The tetramethylcyclobutadiene–C60 monoadduct displays an
open-circuit voltage (0.61 V) and a power conversion efficiency (2.49%)
comparable to the widely used P3HT/PCBM
(poly(3-hexylthiophene/([6,6]-phenyl-C61-butyric acid methyl ester)
composite (0.58 V and 2.57%, respectively). The role of the cofacial
π-orbital interactions between C60 and the attached cyclobutene group was
probed chemically by epoxidation of the cyclobutene moiety and
theoretically through density functional theory calculations. The
electrochemical, photophysical, and thermal properties of the newly
synthesized fullerene derivatives support the proposed effect of
functionalization on electron affinities and photovoltaic performance.