Photovoltaic Effect in a Composite Involving Nonconjugated Conductive Polymer and C60

Abstract

In this thesis, photovoltaic effect in a composite involving nonconjugated conducting polymer and C60 is reported. There has been an intensive research effort in the area of organic photovoltaic cells using conjugated polymers. Here, use of nonconjugated conductive polymers in the photovoltaic cells is being reported for the first time. Composite involving a nonconjugated conductive polymer such as poly(ß-pinene), cis-1,4-poly(isoprene) and SBR, and C60 was formed for use in a photovoltaic cell. The optical absorption and photoluminescence spectra of the films of these composites were studied. When the composites were formed, it was observed that the photoluminescence was totally quenched for the composite involving poly(ß-pinene) and C60 and considerably decreased for the composite involving cis-1,4-poly(isoprene) and C60. The composite involving SBR and C60 did not show as much quenching of photoluminescence. The photovoltaic cell was fabricated using ITO coated glass as one electrode and aluminum as the other, with a nonconjugated polymer-C60 composite film sandwiched between the electrodes. Nitrogen laser (325 nm) and illuminant white light bulbs (200-700nm) were used as the light sources and the photovoltage produced was recorded for different light intensities. The composite involving poly(ß-pinene) and C60 produced better photovoltaic characteristics when compared to the other composites. Among the composites formed by poly(ß-pinene) and C60, the one having 4% of C60 by weight showed the best performance. This can be attributed to the excellent homogeneity of the composite film at this concentration. The photovoltage produced for the composite involving poly(ß-pinene) and 4% C60 by weight was linearly dependent on light intensity. About 280 mV was generated for an intensity of ~ 6mW/sq.cm. Pristine poly(ß-pinene) has a photoluminescence peak at 360 nm for excitation at 280 nm. This photoluminescence is quenched when C60 is added to form the composite with poly(ß-pinene). Therefore, the photovoltaic effect appears to be a result of excited state electron transfer from poly(ß-pinene) to C60. The photovoltaic measurements of the composite involving poly(ß-pinene) and C60 show that these are highly promising for application in low cost photodetectors and photo-sensors when compared to traditional photodetectors. Additional applications will include low cost solar cells.