Stoichiometry dependence of charge transport in polymer/methanofullerene and polymer/C70 derivative based solar cells

Artikel i vetenskaplig tidskrift, 2006

Charge transport in a near IR absorbing polyfluorene copolymer (APFO-Green1) and its blends with methanofullerene [6,6]-Ph C61-butyric acid Me ester (PCBM), and 3'-(3,5-bis-trifluoromethylphenyl)-1'-(4-nitrophenyl)pyrazolino[70]fullerene (BTPF70) is reported. PCBM and BTPF70 are electron acceptor and transporting mols. in polymer based solar cells. The BTPF70 has emerged as a new electron acceptor mol. that provides adequate exciton dissocn. when blended with the low band gap polyfluorene copolymer APFO-Green1. Electron transport in both net PCBM and BTPF70 films are subjected to positional and energetic disorder, with the degree of disorder being more pronounced in BTPF70. On the other hand, mixing PCBM with conjugated polymers usually leads to increased hole mobility. We have investigated and compared the acceptor concn. dependence of charge transport in APFO-Green1/PCBM and APFO-Green1/BTPF70 blend films. For better understanding of the charge transport in the heterojunction films, the field and temp. dependence of hole transport in pure APFO-Green1 films has also been studied. It is obsd. that the behavior of hole mobility in the blend layer is sensitive to the acceptor type. For APFO-Green1/PCBM hole only devices, the hole mobility attains a local max. at 67 wt.% of PCBM, while on the contrary mixing any amt. of BTPF70 with APFO-Green1 results into degrdn. of hole transport. Electron transport in both blends, however, increases monotonically as a function of acceptor loading. [on SciFinder (R)]