Effect of Magnesium Incorporation on Solution-Processed Kesterite Solar Cells.

Raquel Caballero,Victor Izquierdo-Roca,Florian Oliva,Yaroslav E Romanyuk,Stefan G Haass,Laia Arques,Christian Andres

doi:10.3389/fchem.2018.00005

Abstract

The introduction of the alkaline-earth element Magnesium (Mg) into Cu2ZnSn(S,Se)4 (CTZSSe) is explored in view of potential photovoltaic applications. Cu2Zn1−xMgxSn(S,Se)4 absorber layers with variable Mg content x = 0…1 are deposited using the solution approach with dimethyl sulfoxide solvent followed by annealing in selenium atmosphere. For heavy Mg alloying with x = 0.55…1 the phase separation into Cu2SnSe3, MgSe2, MgSe and SnSe2 occurs in agreement with literature predictions. A lower Mg content of x = 0.04 results in the kesterite phase as confirmed by XRD and Raman spectroscopy. A photoluminescence maximum is red-shifted by 0.02 eV as compared to the band-gap and a carrier concentration NCV of 1 × 1016 cm−3 is measured for a Mg-containing kesterite solar cell device. Raman spectroscopy indicates that structural defects can be reduced in Mg-containing absorbers as compared to the Mg-free reference samples, however the best device efficiency of 7.2% for a Mg-containing cell measured in this study is lower than those frequently reported for the conventional Na doping.

Highlights

Kesterite-type material Cu2ZnSn(S,Se)4 (CZTSSe) has been recognized as a promising candidate for low-cost thin-film solar cells due to its large absorption coefficient, tunable band-gap Eg between 1.0 and 1.5 eV adjusted via S/Se-ratio, low toxicity and earth-abundant nature
It was suggested that the substitution of Cu or Zn by other elements as Magnesium (Mg) could suppress the antisite defects CuZn and/or ZnCu formation that limit kesterite solar cells efficiency (Zhong et al, 2016)
The Cu2Zn1−xMgxSn(S,Se)4 thin films absorbers were deposited from the precursor solution with dimethyl sulfoxide (DMSO) as the solvent onto Mo/SiOx/soda-lime glass (SLG) substrates with a subsequent selenization using the methodology described in the previous work (Haass et al, 2015). 1 mm-thick SLG was cleaned in three different supersonic baths at a temperature of 80◦C

Summary

Introduction

Kesterite-type material Cu2ZnSn(S,Se) (CZTSSe) has been recognized as a promising candidate for low-cost thin-film solar cells due to its large absorption coefficient, tunable band-gap Eg between 1.0 and 1.5 eV adjusted via S/Se-ratio, low toxicity and earth-abundant nature. This technology has achieved a 12.6% maximum performance (Wang C. et al, 2014), still far away from that of 22.6% for Cu(In,Ga)Se2 solar cells (Jackson et al, 2016). It was suggested that the substitution of Cu or Zn by other elements as Magnesium (Mg) could suppress the antisite defects CuZn and/or ZnCu formation that limit kesterite solar cells efficiency (Zhong et al, 2016)

Objectives

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Results

Conclusion