Chemically derived graphene oxide (GO) possesses a unique set of properties arising from oxygen functional groups that are introduced during chemical exfoliation of graphite. Large‐area thin‐film ...deposition of GO, enabled by its solubility in a variety of solvents, offers a route towards GO‐based thin‐film electronics and optoelectronics. The electrical and optical properties of GO are strongly dependent on its chemical and atomic structure and are tunable over a wide range via chemical engineering. In this Review, the fundamental structure and properties of GO‐based thin films are discussed in relation to their potential applications in electronics and optoelectronics.
For over 150 years, oxidation of graphite has been known to result in water‐soluble graphite oxide. However, it has been only recently recognized that graphite oxide splits into atomically thin graphene oxide (GO) upon dissolution. GO can be produced on a large scale, handled in solution, assembled into thin films, and deposited on arbitrary substrates. This Review introduces fundamental properties of GO and summarizes recent achievements in device applications.
The electrical properties of solution-processed composite thin films consisting of functionalized graphene sheets (FGS) as the filler and polystyrene (PS) as the host material are described. We ...demonstrate that transistors from graphene-based composite thin films exhibit ambipolar field effect characteristics, suggesting transport via percolation among FGS in the insulating PS matrix. Device characteristics as a function of the FGS size are also reported. The results indicate that devices fabricated using the largest size FGS yield the highest mobility values. This simple and scaleable fabrication scheme based on a commodity plastic could be useful for low-cost, macro-scale electronics.
Two-dimensional (2D) van der Waals transition metal dichalcogenides (TMDs) are a new class of electronic materials offering tremendous opportunities for advanced technologies and fundamental studies. ...Similar to conventional semiconductors, substitutional doping is key to tailoring their electronic properties and enabling their device applications. Here, we review recent progress in doping methods and understanding of doping effects in group 6 TMDs (MX
2
, M = Mo, W; X = S, Se, Te), which are the most widely studied model 2D semiconductor system. Experimental and theoretical studies have shown that a number of different elements can substitute either M or X atoms in these materials and act as n- or p-type dopants. This review will survey the impact of substitutional doping on the electrical and optical properties of these materials, discuss open questions, and provide an outlook for further studies.
Semiconducting two-dimensional (2D) crystals such as MoS2 and WSe2 exhibit unusual optical properties that can be exploited for novel optoelectronics ranging from flexible photovoltaic cells to ...harmonic generation and electro-optical modulation devices. Rapid progress of the field, particularly in the growth area, is beginning to enable ways to implement 2D crystals into devices with tailored functionalities. For practical device performance, a key challenge is to maximize light–matter interactions in the material, which is inherently weak due to its atomically thin nature. Light management around the 2D layers with the use of plasmonic nanostructures can provide a compelling solution.
2D organic–inorganic hybrid perovskites (OIHPs) represent a unique class of materials with a natural quantum‐well structure and quasi‐2D electronic properties. Here, a versatile direct solution‐based ...synthesis of mono‐ and few‐layer OIHP nanosheets and a systematic study of their electronic structure as a function of the number of monolayers by photoluminescence and absorption spectroscopy are reported. The monolayers of various OIHPs are found to exhibit high electronic quality as evidenced by high quantum yield and negligible Stokes shift. It is shown that the ground exciton peak blueshifts by ≈40 meV when the layer thickness reduces from bulk to monolayer. It is also shown that the exciton binding energy remains effectively unchanged for (C6H5(CH2)2NH3)2PbI4 with the number of layers. Similar trends are observed for (C4H9NH3)2PbI4 in contrast to the previous report. Further, the photoluminescence lifetime is found to decrease with the number of monolayers, indicating the dominant role of surface trap states in nonradiative recombination of the electron–hole pairs.
Large ultrathin crystals of (C4H9NH3)2PbI4 (C4PI) and (C6H5(CH2)2NH3)2PbI4 (PEPI) with thickness ranging from a single monolayer to tens of monolayers are synthesized from solution phase. Photoluminescence spectroscopy of individual nanosheets reveals that the electronic gap and exciton binding energy of PEPI are nearly independent of the number of layers, indicating the absence of interlayer screening effects.
Ultrathin layers of van der Waals inorganic semiconductors represent a new class of excitonic materials with attractive light‐emitting properties. Recent observation of valley polarization, optically ...pumped lasing, exciton–polaritons, and single‐photon emission highlights the exciting prospects for two‐dimensional (2D) semiconductors for applications in novel photonic devices. Development of efficient and reliable light sources based on excitonic electroluminescence in 2D semiconductors is of fundamental importance toward the practical implementation of photonic devices. Achieving electroluminescence in these atomically thin layers requires unconventional device designs and in‐depth understanding of the carrier injection and transport mechanisms. Herein, various strategies for electrically generating excitons in 2D semiconducting transition metal dichalcogenides such as monolayer MoS2 are reviewed and challenges and opportunities are outlined. Furthermore, novel device concepts such as tunable chiral emission, electrically driven quantum emission, and high‐frequency modulation are highlighted.
Excitonic van der Waals semiconductors are an attractive building block for constructing on‐chip nanophotonic devices with unconventional functionalities. The recent advances in the understanding and fabrication of excitonic electroluminescent devices based on atomically thin transition metal dichalcogenides such as monolayer MoS2 and WSe2 are reviewed. Various strategies for realizing efficient excitonic emission are discussed.
The integration of novel materials such as single-walled carbon nanotubes and nanowires into devices has been challenging, but developments in transfer printing and solution-based methods now allow ...these materials to be incorporated into large-area electronics. Similar efforts are now being devoted to making the integration of graphene into devices technologically feasible. Here, we report a solution-based method that allows uniform and controllable deposition of reduced graphene oxide thin films with thicknesses ranging from a single monolayer to several layers over large areas. The opto-electronic properties can thus be tuned over several orders of magnitude, making them potentially useful for flexible and transparent semiconductors or semi-metals. The thinnest films exhibit graphene-like ambipolar transistor characteristics, whereas thicker films behave as graphite-like semi-metals. Collectively, our deposition method could represent a route for translating the interesting fundamental properties of graphene into technologically viable devices.
Chemically derived graphene oxide (GO) is an atomically thin sheet of graphite that has traditionally served as a precursor for graphene, but is increasingly attracting chemists for its own ...characteristics. It is covalently decorated with oxygen-containing functional groups - either on the basal plane or at the edges - so that it contains a mixture of sp(2)- and sp(3)-hybridized carbon atoms. In particular, manipulation of the size, shape and relative fraction of the sp(2)-hybridized domains of GO by reduction chemistry provides opportunities for tailoring its optoelectronic properties. For example, as-synthesized GO is insulating but controlled deoxidation leads to an electrically and optically active material that is transparent and conducting. Furthermore, in contrast to pure graphene, GO is fluorescent over a broad range of wavelengths, owing to its heterogeneous electronic structure. In this Review, we highlight the recent advances in optical properties of chemically derived GO, as well as new physical and biological applications.
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