4 - Nanoheterostructured materials based on conjugated polymer and two-dimensional materials: synthesis and applications

Abstract

The heterostructured materials from different semiconductors play a crucial role in semiconductor industry and widely used as building block for electronic and optoelectronic devices. A heterojunction can be made by interfacing two different semiconductors where the electronic band structure near the interface will change according to electrostatics. The semiconductor heterojunctions have been widely used in solid state devices like solar cell, light emitting diode (LED), photo detector, and semiconductor laser. Two-dimensional nanomaterials (2DNMs), typically derived from bulk phase of layered structured materials, have rapidly engrossed as promising materials due to their intriguing physicochemical properties like unique optical band gap structure, good semiconducting ability, extremely strong light–matter interactions, high mechanical strength, and high surface area. Therefore these materials show wide range of potential applications like chemical sensor, biosensor, batteries, supercapacitors, electronic, and optoelectronic devices. With tremendous progress in the discovery and isolation of 2D materials, there exists a wide library of 2DNMs which includes graphene, silicene, germanene, layered transition metal oxides, phosphorene, hexagonal boron nitride (h-BN), graphitic carbon nitride (g-C3N4), layered double hydroxides, transition metal halides, and transition metal chalcogenides. However, one of the main challenges with the 2D materials is their easy restacking possibility resulting from strong interlayer interactions and high surface energy and thereby decreases available active sites. Whereas, there is an urgent need for new and scalable strategies to control the doping and improve the chemical stability of the 2D semiconductors before realizing their promising and fascinating applications. To overcome the above mentioned challenges, 2D materials (2DMs) are functionalized with small molecules, metal nanoparticles, ionic liquids, self-assembled monolayers, and polymers. The advantages of polymers over other functionalization include wide processability in organic solvent or water, ability of patterning using photolithographic techniques. Therefore the hybridization of 2DMs with polymer is one of the elegant approaches to generate new heterostructures with new functionality that can overcome the disadvantages of individual components and boost the activities of both with effectively upgraded properties. There are mainly two approaches (1) covalent and (2) noncovalent methods for interfacing or attaching the polymer on the 2D surface to generate novel polymer/2DM nanoheterostructured materials. Conjugated polymers (CPs) which have delocalized unsaturated π backbone is considered as organic semiconductor in their undoped state and studied enormously for organic electronic, optoelectronic device and supercapacitor applications. Besides good solubility and intrinsic electronic and optoelectronic features of CPs, theoretical molecular dynamics studies reveal that the strength of π-π interactions between conjugated block and 2DM like graphene surface is much stronger and can effectively tailor the band gap of 2DMs. By tuning the intrinsic electronic properties of both 2D semiconductor and CPs attached to 2D surface, it is expected to control the carrier properties at the heterojunctions that lead to generation of new hybrid materials with fascinating and exciting properties. In principle, these heterostructured materials can combine the advantages of 2DMs with that of CPs and provide platform for different applications like electronic devices, sensor, and energy storage. In this chapter, we will focus on the recent advances on synthesis of CP/2DM heterostructures and their applications. Different types of CPs including poly(thiophene)s (PTs) and poly(3-hexylthiophene) (P3HT), polyaniline (PANI), polypyrroles (PPys) were widely used to make hybrid materials with 2DMs through noncovalent π-π interaction. Whereas, CPs with suitable end-functionalized reactive groups were covalently attached with 2DM surface to form heterostructured materials based on CP and 2DNMs.