Energy band alignment engineering in nanostructured hybrid materials based on PbS QDs and reduced graphene oxide: Enhancing photodetector device performance

Abstract

Hybrid materials based on semiconductor quantum dots (QDs) and reduced-graphene-oxide (rGO) have attracted a lot of attention from the scientific community. RGO is compatible with accessible and affordable solution-process methods; additionally, the reduction process allows to manipulate its energy-levels and electrical properties, including majority charge carrier type. These facts, in combination with the known tunability of Eg and the Highest Occupied Molecular Orbital and Lowest Unoccupied Molecular Orbital levels in semiconductor QDs, open novel pathways to improve optoelectronic performance of such nanostructured-hybrid-materials via band alignment engineering. Based on this concept, the effects of different reduction processes on rGO’s electronic properties were studied by Ultraviolet Photoelectron Spectroscopy and Hall effect measurements; additionally, synthesized PbS QDs’ energy levels were measured using electrochemical techniques. Photodetector devices (PD) were fabricated based on the nanostructured-hybrid-materials that showed an improved energy band alignment between rGO and PbS QD’s energy levels; such energy band alignment allowed to improve charge carrier transfer from PbS QDs to rGO upon light absorption, producing photodetectors with improved performance. The devices based on the nanostructured hybrid material reduced thermally at 400 °C displayed the best energy band alignment between the component materials and the lowest resistivity; consequently, showing the highest photocurrent, responsivity, and specific detectivity from all the samples studied.