2D Colloidal Nanocrystal for Optoelectronic and Solar Cell

2D Colloidal Nanocrystal for Optoelectronic and solar CellNovel 2D colloidal nanocrystal for optoelectronic and solar cell applicationsRecently, 2D material has attracted tremendous attention due to their fascinating physicochemical properties. Particularly, the discovery of graphene, a single layer of carbon atoms arranged in a 2D honeycomb lattice has ignited the research on this separate of 2D materials due to extraordinary mechanical, electric and optical properties not spy in their bulk counterparts. Considering graphene is a simple material composed of lonesome(prenominal) carbon element, it cannot satisfy the increasing requirements of diverse applications due to limitations in the versatility and the tunability of composition, organize and functionality in addition to the paradox between the high-mobility FermiDirac electronic grammatical construction and the need for a size-dependent band gap for traditional semiconductor devices. As a result, of paramount importance and interest is to search alternative 2D materials which possess much more than than flexibility and diversity of composition, body complex body part, and functionality. Layered metal dichalcogenides much(prenominal) as WS2 and MoS2 have been extensively investigated. Like graphite, the atoms within the innkeeper layers form strong covalent bonding with relatively weaker interactions between layers such as van der Waals force. Consequently, micromechanical cleavage by Scotch-tape is the some straightforward method to obtain an individual layer while retaining their intrinsic host structure. though it is crucial to evaluate their physical properties, this approach is time-consuming and the yield is too low. More recently, a direct liquid exfoliation where a capable solvent is selected to stabilize cleaved crystallites was proposed to produce nanosheets. This process, comprised of ion-exchange, osmotic swelling, and exfoliation, is useful, but the concentration of unilamella r nanosheet in the firmness of purpose is still very low with the yield no more than a few tens of percentage and the properties of the resulting nanosheets atomic occur 18 dictated by their lift 3D materials, which loses the opportunities to stick out and control over chemical composition and structure. In order to meet the demand for fabrication of functional nanostructured electronic and optoelectronic devices, a facile process to produce large amount of 2D nanocrystal (NC) with supposition of tuning the properties is really imperative.Colloidal chemical synthetic route has been exhibit highly attractive and powerful for their low-cost synthesis to obtain NCs from solution in excellent yield with a good uniformity in terms of chemical composition, surface properties, construct, and size. The complete control over size, shape and structure of the colloidal NCs via tuning reaction chemistry come throughs new-fashioned pathways to design material where size or shape depend ent properties can be exploited. In this get a line, the metal dichalcogenides such as MoS2 and WS2, typically with a trilayer structure of covalently interconnected layers of S, M, and S atoms, go away be the main candidates. High transaction solar cells built from them in 2D NC form is the final goal. As such, colloidal synthetic route leave behind require balance of the reagent excerpt and reaction chemistry to accurately control the growth in the NC. all(prenominal) the advantages of 2D colloidal NCs will be exploited to fabricate solar cells in low cost while retaining efficiencies towards 10%. The objectives of this proposal are as followsDevelop colloidal synthetic routes for 2D colloidal NCs. counterweight the reagent choice and ligand chemistry to achieve NC growth with controllable size, shape, and particularly thickness. cooperate 2D colloidal NCs to device scale area and perform reciprocal material studies with electronic properties ( attack aircraft carrier lifet ime, photoluminescence, carrier mobility).Fabricate all-inorganic NC solar cells and optimize in the device parameter space towards high power conversion efficiency.The project will be divided into three work packages (WPs) with a number of lines in each WP structured to achieve the aims and objectives.Work software product 1 Controllable synthesis delegate 1.1 Develop colloidal synthetic routes to 2D semiconductor NCs.Hot-injection method which involves the injection of a cold solution of precursor molecules into hot liquid will be employed due to the fast formation of nuclei with slow growth of the existing nuclei but not to new nucleation for well controlled size and thickness. The product will be separated by centrifuging and washed up for characterization and analysis by XRD, electron diffraction and HRTEM for structure, and explosive detection system and Raman for chemical composition.Task 1.2 Monitor and control the thickness, doping and their issuance on the optical p roperties.Unlike 0D and 1D NC, in addition to control over composition and structure of 2D NCs, of particular interest is to rationally design and aviation the thickness-dependent optical and electronic properties. For example, few-layer MoS2 has an indirect bandgap, but when it is thinned to single-layer, it becomes direct bandgap leading to compound photoluminesence. In this task we will monitor the effects of the thickness statistical distribution particularly on absorption and photoluminescence (lifetime and QY). The latter will also be used as a metric to decide on the more promising routes for device fabrication, foc employ on highly PL materials as the most promising candidates. In addition, substitutional or interstitial doping of metal sites within 2D NC may be employed to engineer optical characteristics.Work Package 2 Optoelectronic Properties of NC solidsThe presence of covalently bound ligands on the surface of colloidal NC provide a versatile synthetic handle for tail oring the structure, stability, and importantly electronic and optical properties. The deviation of composition and atom arrangement along the terminating boundary and corner sites of 2D colloidal NCs also offers another way to tune their properties. One of the key determinant factors of the performance of solar cells is the carrier mobility. In this task we will investigate ligand exchange strategies utilize ligands that are shorter than 0.3 nm and contain functional head groups such as di-thiol groups and carboxyl-acid based groups. At the same time those functional groups should serve to passivate dangling bonds and therefore their electron-donating closeness will be chosen accordingly. We will monitor the effect of those ligands on carrier mobility by performing CELIV measurements in diode structures resembling an actual solar cell device architecture as well as using FET mobility measurements.In addition to high carrier mobilities NC solids for efficient solar cells call for long carrier lifetimes. Such long lifetimes can be achieved by suppressing trap states and recombination centers typically caused at grain boundaries and interfaces. The role of this task is to monitor the degree of passivation of the ligands utilized with Photoluminescence and PL-lifetime measurements.Work Package 3 photovoltaic device fabrication, testing and optimizingTask 3.1 We will develop simple Schottky and bilayer heterostructures in which the sole photoactive layer is the 2D NC which can be achieved by using a transparent n-type high bandgap semiconductor to form a junction. We will then perform carrier lifetime and recombination-rate characterization employing transient photovoltage and photocurrent measurements.Task 3.2 Optimization of heterojunctions based on 2D NCs.We will perform a device optimization study in which we will study the effect of layer thickness and contact selection to maximize efficiency. The optimized thickness will be sought as a combination of the expected carrier diffusion length and achievable depletion widths based on the mobility, lifetime and carrier density of the semiconductor. Appropriate contacts will be investigated based either on inorganic (MoOx) or organic hole transport layers (electron blocking layers).