Hybrid PCDTBT:PCBM:Graphene-Nanoplatelet Photoabsorbers

Abstract

We study the photoactive properties of poly [N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT): [6,6]-Phenyl-C71-butyric acid methyl ester (PCBM) thin films under ultraviolet irradiation as well as their photo-oxidation, thermal and electrical properties. We compare their stability and performance with composites obtained by integrating graphene nanoplatelets (GNPs). Compared to the pristine polymer, an increase in light absorption and photoluminescence quenching were observed in PCDTBT:PCBM:GNPs. This indicates the occurrence of electron transfer from the conjugated polymer to the empty state of the GNP, through the interfacial bonding based on CH-π and ππ interactions, thereby reducing the photodegradation of the active layer. This is manifested by a significant decline in photo-oxidation, followed by improved thermal stability and suppressed phase separation and aggregation of the PCBM molecules. Atomic force microscopy imaging of the PCDTBT:PCBM:GNPs nanocomposite revealed that graphene flakes enhance the order of the polymeric structures. Finally, we discuss the effect of the GNPs content on the electrical conductivity and electron mobility of the photoactive layer. Our findings offer significant insights into the PV properties and photo physics of hybrid organic bulk-heterojunction solar cells, paving the way towards enhancing their durability and long term performance.