We report measurements of the photovoltaic response of two-layer photocells formed with layers of the conjugated polymer poly(phenylenevinylene), PPV and fullerene, C60, formed between indium-tin oxide and aluminum electrodes. Peak quantum efficiencies of up to ∼9% (electrons collected per incident photon) were measured under short-circuit conditions. We model the photovoltaic response as arising from excitons photogenerated in the PPV layer which are able to diffuse to the interface with the C60 layer where they are ionized. We obtain a value for the exciton diffusion range of 7±1 nm, both from the spectral response and from the absolute efficiency. We demonstrate that the branching ratio for the creation of singlet excitons from absorbed photons is close to unity.
We &pon a stlidy of the photophysical pro$nies of poly(p-phenylene vinylene), PPV, prepared in a way ihai gives an especially high degree of intrachaln order. optical absorption. photoluminescence. photoinduced absorption. and photoconductivity excimion spectra are presented and compared to data reported for leu well ordered wv. SpecM red shib, sharpening of spectral lines, and a msfer of oscillator strength into the vibronic p u n d slates of the electronic transitions are observe$ Photoinduced absorption due to long-lived charged excilations. previously reponed for Less ordered PPV. could not be detected in this material. Photoconductivity excitation specoa show a steep rise at the absorption edge with no appreciable offset between the onsets for photoconductio? and absorption, A very slow photocurrent component is observed, which we associate with lhe trapping and subsequent thermal release of Dhotocarriers.
We have developed modified poly(p-phenylene vinylene) (PPV) to improve its performance in organic electroluminescent devices. Encapsulated single-layer devices with this PPV on indium–tin oxide and a calcium cathode have been operated in air for >7000 h at 20 °C and >1100 h at 80 °C without noticeable degradation. Devices fabricated with this PPV, a conducting polymer layer as anode, and a sputtered low work-function alloy as cathode have efficiencies of over 2 lm/W, brightnesses of >600 Cd/m2 at 4 V, and lifetimes of >1400 h driven at ∼100 Cd/m2 initial brightness.
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