Tunable photogating in a molecular aggregate coupled graphene phototransistor

TL;DR

This study demonstrates a tunable graphene-based photodetector enhanced by a controllably aggregated organic molecular layer, revealing how molecular order influences charge transfer and photodoping mechanisms.

Contribution

It introduces a method to control molecular aggregation on graphene, significantly boosting photodetector response and providing insights into molecular order effects on charge transfer.

Findings

Aggregation level affects photodetector response.

Photodoping mechanisms differ between monomers and aggregates.

Enhanced response due to molecular aggregation control.

Abstract

We present a graphene photodetector coupled to a layer of aggregated organic semiconductor. A graphene phototransistor is covered with a thin film of merocyanine molecules. The aggregation of the molecular layer can be controlled by the deposition parameters and post-deposition annealing to obtain films ranging from amorphous to a highly aggregated state. The molecular layer has a uniaxial structure with excitonic transitions whose transition dipole moments are well defined. The presence of the molecular layer results in an enormous increase in the response of the phototransistor. We further demonstrate that the signal-enhancement is due to p-photodoping of the graphene. The spectroscopic photoresponse suggests that the photodoping via monomers and molecular aggregates takes place differently. Our photodetector is a platform to study the influence of molecular aggregation and order on charge transport processes between aggregated organic semiconductors and two-dimensional materials.