CZTSe solar cells prepared by co-evaporation of multilayer Cu–Sn/Cu,Zn,Sn,Se/ZnSe/Cu,Zn,Sn,Se stacks

Lwitiko P Mwakyusa,Thomas Schnabel,Ulrich W Paetzold,Markus Neuwirth,Willi Kogler,Erik Ahlswede,Michael Hetterich,Bryce S Richards

doi:10.1088/1402-4896/ab2b16

Abstract

In this work, thin-film kesterite Cu2ZnSnSe4 (CZTSe) solar cells were prepared using a novel precursor configuration employing co-evaporated layer stacks of Mo/Cu–Sn/Cu,Zn,Sn,Se/ZnSe/Cu,Zn,Sn,Se. It is found that this sequential deposition of the constituants leads to the formation of large CZTSe grains on the surface and fine grains at the Mo interface of the absorber, respectively. Prototype CZTSe solar cells using this stacked approach achieve power conversion efficiencies of up to 7.9% at an open-circuit voltage of 430 mV and a fill-factor of 62%. The analysis of temperature-dependent current density–voltage characteristics indicates that bulk Schottky–Read–Hall recombination is the dominant recombination mechanism for the devices fabricated from the proposed stack. In addition, the influence of pre-annealing of each stacked layer on the absorber growth and device performance is examined and discussed.

Highlights

As a result of the United Nations climate summit in Paris, an agreement to decrease CO2 emission, the main contributor to global warming, was approved in 2016
Prototype CZTSe solar cells using this stacked approach achieve power conversion efficiencies of up to 7.9% at an open-circuit voltage of 430 mV and a fill-factor of 62%
In this study we introduced a precursor stack utilizing a configuration of Mo/Cu–Sn/Cu, Zn, Sn, Se/ZnSe/Cu, Zn, Sn, Se with the motivation of: (i) allowing formation of CZTSe via a ternary path due to the presence of a Cu–Sn alloy at the back interface; and (ii) a delayed formation of CZTSe at the Mo back contact to mitigate an early interaction of CZTSe and Mo, possibly reducing the decomposition of CZTSe at the rear interface

Summary

Introduction

As a result of the United Nations climate summit in Paris, an agreement to decrease CO2 emission, the main contributor to global warming, was approved in 2016. The latter provides more than 1% of the global energy, with around 7%–8% in some of the developed countries [1]. Despite the highly optimized fabrication process of Si-based devices with laboratory efficiencies (h) up to 26.9% for monocrystalline Si and 22.3% for multicrystalline Si, respectively [3], this approach suffers from poor light absorption due to the indirect bandgap of the Si absorber. A high absorber thickness is required in order to achieve good efficiencies, limiting the utilization of Si technology for flexible applications. Thin-film technologies such as cadmium telluride (CdTe), Cu(In,Ga)(S,Se) (CIGS), and more recently

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Conclusion