Comparing strategies for improving efficiencies in vacuum processed Cu2ZnSnSe4 solar cells

Louis Grenet,Fabrice Emieux,Frédéric Roux,Md Abdul Aziz Suzon

doi:10.1063/1.5034526

Abstract

In this study, we detail a Cu2ZnSnSe4 based solar cell fabrication process based on the selenization of metallic precursor stacks with elemental Se. 9.4% efficient devices without antireflection coating have been obtained. First, reproducibility issues of the process are carefully shown and discussed. It is demonstrated that device performances are strongly impacted by the precise control of the precursor composition. Then, starting from this robust process, a review of existing strategies to improve kesterite efficiencies is conducted. A significant increase in efficiency (+1.4% absolute efficiency and +50 mV VOC) is obtained with absorber surface treatment and post-annealing, while no effect of Ge incorporation in the precursor stack is observed. This contradictory result to most of the recent publications raises the question of the universality of this strategy to improve kesterite solar cell performance. Finding a universal activation step to boost kesterite efficiencies and bring it to the market remains a crucial need for the community.

Highlights

In the past decade, the Cu2ZnSn(S,Se)4 (CZTSSe) absorber has attracted a lot of attention in the thin film photovoltaic (PV) community because of its potential to replace the1941-7012/2018/10(4)/043503/10/$30.00Published by AIP Publishing.043503-2 Grenet et al.J
we detail a Cu2ZnSnSe4 based solar cell fabrication process based on the selenization of metallic precursor stacks
It is demonstrated that device performances are strongly impacted by the precise control

Summary

INTRODUCTION

The Cu2ZnSn(S,Se) (CZTSSe) absorber has attracted a lot of attention in the thin film photovoltaic (PV) community because of its potential to replace the. To this purpose, a very precise description of our reference CZTSe solar cell fabrication process with particular attention paid to the reproducibility issues is first given before the implementation of the aforementioned strategies to improve efficiencies of our devices. We described a CZTSSe synthesis process based on the selenization of ZnS/Cu/Sn stacks of precursors deposited by radio-frequency sputtering and e-beam evaporation, leading to devices with power conversion efficiencies of 6.0%12 and 7.0%.13. Despite these promising results, precursor stacks have been recently replaced by pure metallic (Cu, Zn, and Sn) stacks fully deposited by direct-current sputtering in order to make the process more compatible with industrialization (deposition time and homogeneity).

Sample preparation

Characterization

Baseline process and alternative routes

Surface etching and post-treatment annealing

Best devices

CONCLUSION