The photovoltaic behavior of vacuum deposited diphenyl-diketo-pyrrolopyrrole polymer

Diphenyl-diketo-pyrrolopyrroles (DPP) are low molecular weight materials with promising luminescence and photovoltaic properties which are suitable for thin layer fabrication by a variety of methods like solution processed spin coating and physical vapour deposition (PVD). In this paper we investigate two types of Indium tin oxide (ITO)|Active material|Al structures: one with DPP derivative as active polymer layer with thicknesses of about 150nm and a second type of heterojunction solar cell based on DPP-C60 composite films (ratio 60:40 mass %) with thicknesses of about 100nm. The samples in this study have been prepared by the means of PVD which has the capability to produce the whole multilayered structure in one vacuum cycle after which the samples were processed and encapsulated within inert atmosphere in a glove box. The surface morphology of the films was studied by Scanning Electron Microscope (SEM) imaging which revealed formations of grains with size of about 200-500nm in the DPP layers and spheres with size of about 100-200nm in the composite layer. The photovoltaic behavior was evaluated through the results of spectral sweep of the generated photocurrent and I-V characteristics in dark and under illumination with specific wavelength. The photovoltaic behavior was successfully demonstrated and directions toward performance improvements have been given.