Enhanced photovoltaic performance of bulk heterojunction based on ZnS quantum dots-grafted graphene

ZnS quantum dots (QDs) and ZnS:graphene QDs were synthesized successfully via simple sonochemical method. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) analysis revealed the average size of ZnS and ZnS:graphene QDs of the order of 3.7 nm and 8.4 nm, respectively. The band gap of ZnS:graphene QDs was tuned to 4.9 eV. Fourier transform infrared (FTIR) analysis confirms the formation of single phase ZnS QDs. The significant increase in conductivity of the order of 104 S/cm was observed in ZnS:graphene QDs. The bulk heterojunction devices ITO/PEDOT:PSS/P3HT:ZnSQDs/Al and ITO/PEDOT:PSS/P3HT:(ZnS:graphene)QDs/Al were fabricated. Here we demonstrate the increase in current density (from 2.44 μA/cm2 to 98.4 μA/cm2), alongwith the lower turn on voltage (decrease from 0.40 V to 0.12 V) by using the ZnS:graphene QDs as compared to pristine ZnS QDs in the active layer. Furthermore, this enhancement in current density shows that the ZnS:graphene QDs have a great potential for active layer in photovoltaic devices.