Photoelectric Properties of Heterostructures Based on PEPC and MEH-PPV Films Doped with Zinc Octabutylphthalocyanine

Abstract

Abstract. Planar organic heterostructures have been prepared using poly-N-epoxypropylcarbazole fi lms and poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] by the method of successive deposition adding 2,3,9,10,16,17,23,24-zinc octabutylphthalocyanine. Photoelectric, photodielectric and photovoltaic properties of the heterostructures have been studied. It has been found that the structure photosensitivity in the red part of spectrum is remarkably enhanced by adding the metal complex into the -conjugate polymer. It has also been established that metal sensitizers are capable of slowing down the photovoltaic rise and decay transients exhibited after the illuminating light is switched on and off, respectively. The likely origin of these effects is suggested, relating to deep traps generated by the metal complex.Keywords: organic heterostructures, MEH-PPV, metal complexes, photovoltaic effect. IntroductionOver the last decades, the considerable effort has been devoted to the development of low-cost and fl exible organic photonic devices based on molecular composition of aromatic and heteroaromatic compounds absorbing light within the solar range. Quite recently, the superior photovoltaic performance has been demonstrated employing phthalocyanines, and the new class of conjugate polymers containing para-phenylenevinylene (PPV), porphyrin and fullerene fragments have been reported [1][2][3][4]. One of the most popular material of this type is poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) with the long-wavelength absorption edge occurred at about 600 nm.It has been previously reported that MEH-PPV-based fi lm structures reveal the photoelectric effect, and the photovoltage (PV) have been observed in these structures [5]. In order to shift the photosensitivity spectrum of this material to the near infrared, the polymer composite fi lms (PCF) doped by organic dyes or metal complexes have been usually employed [6][7][8][9][10][11]. The occurrence of the light absorbing centres and the resulting generation of electron-hole (e-h) pairs provide the pathways for the inner photoeffect sensitizing observed in PCF. The effectiveness of the lightelectricity transformation is mainly determined by the e-h pair lifetime. The lifetime can be considerably enhanced by introducing the hetero-interface, consisting of two PCF with different electronic properties. In this case, the transport probability for carriers, moving from one PCF to the other one, depends upon the energy barriers occurring at the interface and can reduce the geminate recombination probability of the carriers.This type of heterostructures can be designed using, e.g. MEH-PPV and carbazolyl-containing polymers or oligomers (for example, poly-N-epoxypropyl-carbazole, PEPС). The fi rst structure possesses both the electron and whole conductivity, whereas the second one is solely of p-type. Despite the large number of papers regarding the photovoltaic devices with carbazolyl groups [12], there is a lack of experimental studies aimed to in...