Tetrafullerene conjugates for all-organic photovoltaics.
The synthesis of two new tetrafullerene nanoconjugates in which four C60 units are covalently connected through different pi-conjugated oligomers (oligo(p-phenylene ethynylene) and oligo(p-phenylene vinylene)) is described. The photovoltaic (PV) response of these C60-based conjugates was evaluated by using them as the only active material in organic solar cells, showing a low PV performance. Photophysical studies in solution demonstrated a very fast ( approximately 10 ps) deactivation of the singlet excited state of the central core unit to produce both charge-separated species (i.e., C60*--oligomer+*-(C60)3 and C60 centered singlet excited states). The charge-separated state recombines partly to the C60 centered singlet state that undergoes subsequent intersystem crossing. Photophysical studies carried out in films support these data, exhibiting long-lived triplet excited states. For both tetrafullerene arrays, the low yield of long-lived charge carriers in thin films accounts for the limited PV response. On the contrary, utilizing the oligo(p-phenylene vinylene) centered precursor aldehyde as an electron donor and antennae unit and mixing with the well-known C60 derivative PCBM, the photophysical studies in films show the formation of long-lived charges. The PV devices constructed from these mixtures showed a relatively high photocurrent of 2 mA cm(-2). The sharp contrast between the nanoconjugates and the physical blends tentatively was attributed to improved charge dissociation and the collection of more favorable energy levels in the blends as a result of partial aggregation of both of the components.
Fernandez
Gustavo
G
Departamento de Química OrgAnica, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, Ciudad Universitaria s/n, 28040-Madrid, Spain.
Sanchez
Luis
L
Veldman
Dirk
D
Wienk
Martijn M
MM
Atienza
Carmen
C
Guldi
Dirk M
DM
Janssen
René A J
RA
Martín
Nazario
N
D037741:Fullerenes / Q000737:chemistry*; D015394:Molecular Structure; D009930:Organic Chemicals / Q000737:chemistry*; D010084:Oxidation-Reduction; D010777:Photochemistry; D012996:Solutions; D013053:Spectrophotometry; D013696:Temperature
D037741:Fullerenes; D009930:Organic Chemicals; D012996:Solutions