Metal Domain Size Dependent Electrical Transport in Pt-CdSe Hybrid Nanoparticle Monolayers

Abstract

Thin films prepared of semiconductor nanoparticles are promising for low-cost electronic applications such as transistors and solar cells. One hurdle for their breakthrough is their notoriously low conductivity. To address this, we precisely decorate CdSe nanoparticles with platinum domains of one to three nanometers in diameter by a facile and robust seeded growth method. We demonstrate the transition from semiconductor to metal dominated conduction in monolayered films. By adjusting the platinum content in such solutionprocessable hybrid, oligomeric nanoparticles the dark currents through deposited arrays become tunable while maintaining electronic confinement and photoconductivity.Comprehensive electrical measurements allow determining the reigning charge transport mechanisms.Keywords: Colloidal hybrid nanoparticles, electrical transport, photoconductivity, size effects, Langmuir-Blodgett deposition 2 Continuous progress in the control of nanoparticle (NP) size, composition, and shape has led to unprecedented possibilities in material design targeting applications as diverse as medical therapy and diagnostics and solid state devices. 1 Nanoparticle thin-film devices are studied and applied in various contexts, especially with regard to their optoelectronic and electronic properties. 2 The solution processability of nanoparticle building blocks makes them particularly attractive for applications such as photovoltaics, 3-6 light emitting diodes, 7-9 as well as chemical sensing and photodetection. [10][11][12][13][14] The fundamental electrical properties of single material systems consisting of either semiconductor or metal nanoparticles have been studied especially with respect to quantum-mechanical coupling phenomena, [15][16][17][18][19][20] Coulombblockade behavior, 21,22 transistor characteristics, [23][24][25] and photo conductivity. 20,26,27 Nanoparticles prepared by colloidal chemistry can be arranged into ordered arrays by a variety of methods. Among them are the widely applied spin-coating, self-assembly, 28,29 and the Langmuir-Blodgett technique. 30 In particular, the latter relies on a stabilizing layer of organic surfactants that enables the dispersion and assembly of nanoparticles on a liquid sub-phase. While highly ordered films can be achieved, a big drawback of this method is the creation of spatial and energetic barriers between adjacent nanoparticles by the organic stabilizers. This usually leads to a high resistivity of the arrays. 31 (CZTS) and Au were recently reported to improve the photoresponse and -stability compared to pure CZTS multi-layered photodetectors. 51 Increasing the current in a semiconductor nanoparticle array by deposition of metallic domains seems intuitive. Anyhow, it is less clear how the metal domain size and thus the degree of coupling between the domains influences the dark and especially the photocurrents. In the following, we report on the synthesis of well-defined oligomeric Pt-CdSe HNPs by a simple seeded-growth approach and the effect of Pt domain size ...

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