In this study, some crucial parameters were determined of flexible polymer–organic solar cells prepared from an active layer blend of poly(3-hexylthiophene) (P3HT) and the fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) mixed in 1:1 mass ratio and deposited from chlorobenzene solution by spin-coating on poly(ethylene terephthalate) (PET)/ITO substrates. Additionally, the positive effect of an electron transport layer (ETL) prepared from zinc oxide nanoparticles (ZnO np) on flexible photovoltaic elements’ performance and stability was investigated. Test devices with above normal architecture and silver back electrodes deposed by magnetron sputtering were constructed under environmental conditions. They were characterized by current-voltage (I–V) measurements, quantum efficiency, impedance spectroscopy, surface morphology, and time–degradation experiments. The control over morphology of active layer thin film was achieved by post-deposition thermal treatment at temperatures of 110–120 °C, which led to optimization of device morphology and electrical parameters. The impedance spectroscopy results of flexible photovoltaic elements were fitted using two R||CPE circuits in series. Polymer–organic solar cells prepared on plastic substrates showed comparable current–voltage characteristics and structural properties but need further device stability improvement according to traditionally constructed cells on glass substrates.
ZnO has been widely used as electron selective material in P3HT:PCBM organic solar cells with either conventional or inverted architecture in order to enhance the extraction of electrons and block the collection of holes at one electrode. In this work we investigate the influence of ZnO nanoparticles electron transport layer (ETL) on the performance and stability of P3HT:PCBM based organic solar cells with conventional architecture and magnetron sputtered back Ag contacts. Their stability in the dark and under real outdoor conditions was monitored by current-voltage measurements and impedance spectroscopy. The impedance spectra were taken as a function of applied bias under illumination in order to reveal more information about the degradation mechanisms taking place in the device.
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