Ultra‐small CuO nanoparticles with tailored energy‐band diagram synthesized by a hybrid plasma‐liquid process

Abstract

CuO is a versatile p-type material for energy applications capable of imparting diverse functionalities by manipulating its band-energy diagram. We present ultrasmall quantum confined cupric oxide nanoparticles (CuO NPs) synthesized via a simple one-step environmentally friendly atmospheric pressure microplasma synthesis process. The proposed method, based on the use of a hybrid plasma-liquid cell, enables the synthesis of CuO NPs directly from solid metal copper in ethanol with neither surfactants nor reducing agents. CuO NPs films are then used for the first time in all-inorganic third generation solar cell devices demonstrating highly effective functionalities as blocking layer. K E Y W O R D Sband structure, cupric oxide quantum dots, one step-green synthesis, quantum dots/inorganic solar cells | INTRODUCTIONTransition metal oxides, due to their inertness, stability, raw material abundance, and low-cost, are highly desirable materials for many applications, for example, solar cells, supercapacitors, light emitting diodes, photodetectors, field effect transistors, batteries and bio and gas sensors, among others. [1][2][3][4][5][6][7][8][9][10] Furthermore, as with other materials, at the nanoscale, metal-oxides can present interesting, important and tunable size-dependent optoelectronic properties. [7,11,12] Metal-oxides are generally characterized by very wide bandgaps, whereas CuO is a p-type low bandgap (∼1.2 eV in bulk form) and nontoxic material. [13][14][15][16][17][18] The possibility of manipulating the CuO bandgap, through quantum confinement, from 1.2 (bulk) to >2 eV [13,[16][17][18][19][20][21][22] is an exciting opportunity as it would make CuO a highly versatile and attractive material for a range ofThe copyright line for this article was changed on 20 April, 2017 after original online publication.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. applications; for instance, it would be possible to use CuO nanoparticles with tunable properties as absorber or transport/ blocking layers in photovoltaic devices.Various physical, chemical, and physicochemical techniques have been employed for synthesizing CuO nanostructures with varying size and shape. [16,18,20,23,24] However, these techniques suffer from numerous disadvantages including complex and time consuming steps, high temperatures, inert atmosphere, expensive source materials, toxic organic solvents, and surfactants. [23,25,26] Furthermore, the control of the resulting morphology, crystallinity, and agglomeration of the nanostructures is a significant challenge which demands additional cleaning steps to remove undesired by-products and chemical impurities or residues. [23,[26][27][28][29] The presence of surfactant or ligand chemistries is essential for minimizing particle coalescence and agglomeration during standard colloid synthesis; however, such chemistries impact significantly on the res...

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