Highly Efficient\nSolar Energy Harvesting in Phosphorene–Graphene\nQuantum Dot van der Waals Heterostructures: An Ab Initio Approach

This study delves into the intricacies of creating highly\neffective\npower conversion assemblies from van der Waals heterostructures of\nphosphorene and graphene quantum dots by employing density functional\ntheory calculations. We emphasize the role of individual monomer properties\nand their interlayer interactions in the power conversion ability\nby focusing on visible light absorption, charge carrier generation,\nand their separation. Different edge atom functionalization (H, NH<sub>2</sub>, Cl, OCN, CN) in the phosphorene quantum dots and heteroatom\ndoping (Group IV = Si, Ge, and Group VI = O, S, Se) in the basal plane\nof graphene quantum dots were employed to alter the monomer properties.\nOur results indicate that select combinations of these modification\ntechniques yield staggered frontier molecular orbital alignments (Type\nII) with spatial separation of the highest occupied and lowest unoccupied\nmolecular orbitals. These candidates possess an improved visible light\nabsorption range with reduced intensities owing to the dominance of\ncharge transfer excitations. Edge functionalization of phosphorene\nwas identified as the most significant contributor to interlayer interaction\nstrength, with functional groups that are electron-withdrawing in\nnature forming stronger interactions. Heteroatom doping of graphene\nwas recognized as the most important contributor to improving visible\nlight absorbance owing to the reduction in fundamental gaps. From\nthe candidates considered, systems with relatively weaker interlayer\ninteractions were determined to be better at charge carrier separation\ndue to the potential gradient being concentrated at the interfacial\nregion. These systems possess approximated power conversion efficiencies\nranging between 11 and 29%, among the highest reported for quantum\ndot systems characterized by density functional theory calculations.