Marked Enhancement of Photoconductivity and Quenching of Luminescence in Poly(2,5-dialkoxy-p-phenylene vinylene) upon C₆₀ Doping

Abstract

Surface acoustic wave (SAW) properties of z -cut LiNbO 3 waveguides fabricated by proton exchange using octanoic acid are investigated. The phase velocity V p and electromechanical coupling coefficient K 2 of SAWs are significantly decreased by the increase of kd , where k is the wavenumber (2π/λ) and d is the waveguide depth. The insertion loss IL of a SAW is increased by the increase of kd and becomes nearly constant at kd ≥ 0.13. The temperature coefficient of delay TCD of a SAW calculated from the frequency change shows an apparent increase with kd , reaching a maximum at kd = 0.213, then slightly decreasing at higher kd . On the other hand, the effects of annealing on V p and IL are also investigated. The results show that post-annealing can result in a restoration of the decreased V p and an improvement of IL.

Loading Fullerene into a Conjugated Polymer Without Chemical Modification

“…Although the photoluminescence from the MEH-PPV colloids was weakened by the introduction of the C 60 colloids, as shown in Figure 4a, the emission from MEH-PPV was only weakened by a factor of 10 %, even when the suspension contained 50 mol-% of C 60 . As reported by Yoshino et al, [6] C 60 doping of 5 mol-% is enough to almost completely quench the photoluminescence from this type of poly(p-phenylenevinylene) derivative. Thus, it can be concluded that the C 60 in these suspensions is a less effective luminescence quencher.…”

“…A few years after the theoretical proposal of this strategy, [4] the fullerene C 60 was the first suitable acceptor material found for conjugated polymers, [5±8] leading to an almost complete quenching of photoluminescence as well as a dramatic enhancement of the photon±electron conversion efficiency (more than two orders of magnitude above that of the polymer itself upon doping with a few mol-%). [5,6] In this case, the electrons in the conjugated polymer were transferred to the fullerene, and the remaining holes became photocarriers migrating along the polymer chains. Because of the low fullerene concentration in the composite, the fullerene electrons do not play a role as photocarriers.…”

Exciton dissociation, charge transport, and recombination in ultrathin, conjugated polymer-TiO2nanocrystal intermixed composites

“…In related work, a PPV derivative with C 60 molecules blended in at high weight fractions forms the active medium of photovoltaic devices with high quantum yields. [10][11][12] In a previous study, we showed directly, using a microwave conductivity technique, that excitons generated in PPV will dissociate at a TiO 2 nanocrystal interface with electrons transferred to the nanocrystals. 13 We are also able to time resolve the dynamics of the recombination process using the same technique, a complex process which occurs on a time scale of hundreds of nanoseconds to microseconds.…”

On the Importance of Morphology Control in Polymer Solar Cells

“…[21] The typical exciton diffusion length in most organic semiconductors is, however, limited to 5-20 nm. [22][23][24][25] Consequently, acceptor/donor interfaces have to be within this diffusion range for efficient exciton dissociation into free charges; however, efficient light absorption only can be guaranteed for photoactive layers with thickness larger than 200 nm. Independently, Yu and Heeger [26] and Halls et al [27] have addressed the problem of limited exciton diffusion length by intermixing two conjugated polymers with different electron affinities or a conjugated polymer with C 60 molecules or their methanofullerene derivatives.…”