Effect of Sodium Treatment on the Performance of Electrostatic Spray Assisted Vapour Deposited Copper-poor Cu(In,Ga)(S,Se)2 Solar Cells

Mingqing Wang,Md. Anower Hossain,Kwang-Leong Choy

doi:10.1038/s41598-017-07027-9

Mingqing Wang, Md. Anower Hossain + Show 1 more

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https://doi.org/10.1038/s41598-017-07027-9

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Journal: Scientific Reports	Publication Date: Jul 28, 2017
Citations: 24	License type: open-access

Affiliation: University College London

Abstract

In our work, eco-friendly, non-vacuum and low cost Electrostatic Spray Assisted Vapour Deposition (ESAVD) method has been used to produce Cu(In,Ga)(S,Se)2 (CIGS) solar cells. Copper (Cu) deficient (Cu/In + Ga = 0.76) CIGS films were designed to avoid the rather dangerous KCN treatment step for the removal of conductive minor phases of Cu2S/Cu2Se. A simple sodium (Na) treatment method was used to modify the morphology and electronic properties of the absorber and it clearly improved the solar cell performance. The SEM and XRD results testified a slightly increase of the grain size and (112) crystal orientation in the Na-incorporated CIGS thin films. From the Mott-schottky results, it can be seen that the functions of the Na treatment in our non-vacuum deposited CIGS are mainly used for defect passivation and reduction of charge recombination. Photovoltaic characteristics and j-V curve demonstrated that the dipping of CIGS films in 0.2 M NaCl solution for 20 minutes followed by selenization at 550 °C under selenium vapor resulted in the optimum photovoltaic performance, with jsc, Voc, FF and η of the optimized solar cell of 29.30 mA cm−2, 0.564 V, 65.59% and 10.83%, respectively.

Highlights

Still hazardous in case of contact and are not environmentally friendly
In the Electrostatic Spray Assisted Vapour Deposition (ESAVD) process, the CIGS films were intentionally prepared with slightly Cu-poor condition(Cu/In + Ga = 0.76) than usual(Cu/In + Ga > 0.80) and the Cu content in the precursor solution was adjusted which eliminates the formation of Cu2−xSe and avoids the use of the dangerous KCN post-treatment step
The best solar cell efficiency of 10.83% has been achieved with the optimum Na treatment condition, which will accelerate the industrilization of ESAVD research into fully non-vacuum-based CIGSSe thin film solar cells and our findings will pave the way for dramatic improvements of the efficiency of other non-vacuum deposited chalcogenide films

Summary

Introduction

Still hazardous in case of contact and are not environmentally friendly. Hot injection is one of the popular methods to make CIGS nanoparticles. After the subsequent post-selenization and KCN treatment of the deposited CIGS thin films, solar cells based on hot injection method demonstrate a maximum energy conversion efficiency of 15%19. The use of an electric field during the deposition helps to direct the chemical precursor toward the well-defined area of the heated substrate, enabling high deposition efficiency (e.g., above 90%) at optimum deposition conditions Such high deposition efficiency of the ESAVD process is especially valuable for CIGS films, for which the indium (In) and gallium (Ga) constituents are expensive and the elemental content in the earth is comparatively low. By optimizing deposition conditions and composition in the precursor, CIGS solar cells with efficiency above 8% have been achieved by the ESAVD method[22]. CIGS absorber was characterized by Energy Dispersive X-Ray spectroscopy (EDX)

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