Increasing the Solubility Limit for Tetrahedral Aluminium in ZnO:Al Nanorods by Variation in Synthesis Parameters

Anke Kelchtermans,Ken Elen,Joke Hadermann,Daniel Slocombe,Peter Adriaensens,Marlies K. Van Bael,Alexander Riskin,Vladimir L. Kuznetsov,An Hardy,Peter P. Edwards

doi:10.1155/2015/546041

Anke Kelchtermans, Ken Elen + Show 8 more

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https://doi.org/10.1155/2015/546041

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Abstract

Nanocrystalline ZnO:Al nanoparticles are suitable building blocks for transparent conductive layers. As the concentration of substitutional tetrahedral Al is an important factor for improving conductivity, here we aim to increase the fraction of substitutional Al. To this end, synthesis parameters of a solvothermal reaction yielding ZnO:Al nanorods were varied. A unique set of complementary techniques was combined to reveal the exact position of the aluminium ions in the ZnO lattice and demonstrated its importance in order to evaluate the potential of ZnO:Al nanocrystals as optimal building blocks for solution deposited transparent conductive oxide layers. Both an extension of the solvothermal reaction time and stirring during solvothermal treatment result in a higher total tetrahedral aluminium content in the ZnO lattice. However, only the longer solvothermal treatment effectively results in an increase of the substitutional positions aimed for.

Highlights

Because of the coexistence of high conductivity and high transparency in the visible region, the realization of transparent conductive oxides (TCOs) has attracted much interest for optoelectronic device applications, such as solar cells and displays [1,2,3]
The spectra of the ZnO:Al nanorods obtained after longer solvothermal reaction times (48 h and 96 h) on the other hand exhibit a broad additional absorption band between 600 and 3000 cm−1 which can be attributed to surface plasmon IR absorptions originating from free charge carriers
It is assumed that only substitutional Al contributes to the formation of charge carriers. This leads to the conclusion that a longer solvothermal reaction time leads to a higher content of substitutional aluminium, which should be beneficial for the conductivity [20, 21]

Summary

Introduction

Because of the coexistence of high conductivity and high transparency in the visible region, the realization of transparent conductive oxides (TCOs) has attracted much interest for optoelectronic device applications, such as solar cells and displays [1,2,3]. While the synthesis of ZnO:Al nanocrystals and films has recently advanced markedly, it still remains a challenge to control dopant incorporation in zinc oxide based TCO NCs [8,9,10,11,12,13,14,15,16]. Besides the substitutional tetrahedral position, the aluminium ions can occupy empty interstitial tetrahedral and octahedral sites in the hexagonal wurtzite structure of ZnO. In these positions they will act as an acceptor, decreasing the conductivity [18, 20, 22]

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