Abstract

In recent years, the search for more efficient and environmentally friendly materials to be employed in the next generation of thin film solar cell devices has seen a shift towards hybrid halide perovskites and chalcogenide materials crystallising in the kesterite crystal structure. Prime examples for the latter are Cu2ZnSnS4, Cu2ZnSnSe4, and their solid solution Cu2ZnSn(SxSe1−x)4, where actual devices already demonstrated power conversion efficiencies of about 13 %. However, in their naturally occurring kesterite crystal structure, the so-called Cu-Zn disorder plays an important role and impacts the structural, electronic, and optical properties. To understand the influence of Cu-Zn disorder, we perform first-principles calculations based on density functional theory combined with special quasirandom structures to accurately model the cation disorder. Since the electronic band gaps and derived optical properties are severely underestimated by (semi)local exchange and correlation functionals, supplementary hybrid functional calculations have been performed. Concerning the latter, we additionally employ a recently devised technique to speed up structural relaxations for hybrid functional calculations. Our calculations show that the Cu-Zn disorder leads to a slight increase in the unit cell volume compared to the conventional kesterite structure showing full cation order, and that the band gap gets reduced by about 0.2 eV, which is in very good agreement with earlier experimental and theoretical findings. Our detailed results on structural, electronic, and optical properties will be discussed with respect to available experimental data, and will provide further insights into the atomistic origin of the disorder-induced band gap lowering in these promising kesterite type materials.

Highlights

  • The ongoing quest to identify more efficient and environmentally friendly materials to be employed in solar cell devices has shifted the focus in recent years towards quaternary chalcogenides and hybrid halide perovskites

  • In recent years, the search for more efficient and environmentally friendly materials to be employed in the generation of thin film solar cell devices has seen a shift towards hybrid halide perovskites and chalcogenide materials crystallising in the kesterite crystal structure

  • Our calculations show that the Cu-Zn disorder leads to a slight increase in the unit cell volume compared to the conventional kesterite structure showing full cation order, and that the band gap gets reduced by about 0.2 eV, which is in very good agreement with earlier experimental and theoretical findings

Read more

Summary

Introduction

The ongoing quest to identify more efficient and environmentally friendly materials to be employed in solar cell devices has shifted the focus in recent years towards quaternary chalcogenides and hybrid halide perovskites. While hybrid halide perovskites face stability issues due to their admixed organic molecules, chalcogenide materials exhibit intrinsic structural properties, which have prevented their large-scale application in solar cell devices so far. Concerning the latter, Cu2 ZnSnS4 (CZTS) and Cu2 ZnSnSe4 (CZTSe) are prominent examples, and with band gaps of about 1.0 eV (CZTSe) [1,2] and 1.53 eV . A recently devised technique to speed up hybrid functional calculations for materials science investigations [19] provided the motivation for the current work, namely the reevaluation of Cu-Zn disorder in CZTSe employing first-principles calculations based on DFT and special quasirandom structures to model the structural disorder.

Kesterites and the Cu-Zn Disorder
How to Speed Up Hybrid Functional Calculations
Other Computational Details
Bulk Structural Properties
Disordered Structural Properties
Electronic and Optical Properties
Summary and Outlook
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call