Organic polymer bilayer structures for applications in flexible solar cell devices

Abstract

We report flexible organic solar cells composed of MEH-PPV (poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenyl vinylene]) and PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)) as photoactive layer and hole transport layer, respectively, fabricated using a simple solution processing method on flexible polyethylene terephthalate (PET) substrates. The current–voltage characteristics have been studied in PET based flexible devices having four different kind of structures such as graphene/PEDOT:PSS/PET, graphene/PEDOT:PSS/PEDOT:PSS/PET, graphene/MEH-PPV/PEDOT:PSS/PET and graphene/MEH-PPV/PEDOT:PSS/PEDOT:PSS/PET. Under AM 1.5G solar illumination, the devices with structure graphene/MEH-PPV/PEDOT:PSS/PEDOT:PSS/PET exhibits an open-circuit voltage (Voc) of 2.549 V, a short-circuit current density (Jsc) of 0.11 mAcm−2, and a fill factor (FF) of 56.7%. The device shows an ideality factor of ~35 along with a diode reverse saturation current of 0.067 × 10−6 μA. We propose that incorporation of MEV-PPV into graphene and PEDOT:PSS based Schottky junction forming a double layer polymer structure, responsible for enhanced current conductionby replacing metallic nanoparticle into polymer blend leads to the significant improvement in solar output characteristics of the devices. In these bilayer structures metallic nanoparticles are not embedded into the polymer matrix and therefore it enhances the device stability and lifetime by eliminating the issues of phase separation between nanoparticles and polymers.