Study of the opto-electronic properties of Cu2ZnXS4 (X=Sn,Ge,Si) kesterites as input data for solar cell efficiency modelling

(1)

thomas.ratz@uliege.be

Study of the opto-electronic properties of Cu

₂

ZnXS

₄

(X=Sn,Ge,Si)

kesterites as input data for solar cell efficiency modelling

Thomas Ratz1,2_{, Jean-Yves Raty}1,3_{, Guy Brammertz}4_{, Bart Vermang}2,4,5_{, Ngoc Duy Nguyen}1

1. CESAM | Q-MAT | Solid State Physics, Interfaces and Nanostructures, Physics Institute B5a, Allée du Six Août 19, B-4000 Liège, Belgium 2. Institute for Material Research (IMO), Hasselt University, Agoralaan gebouw H, B-3590 Diepenbeek, Belgium

3. University of Grenoble Alpes | CEA-LETI | MINATEC Campus | Rue des Martyrs 17, F-38054 Cedex 9 Grenobles, France 4. IMEC division IMOMEC | partner in Solliance, Wetenschapspark 1, B-3590 Diepenbeek, Belgium

5. Energyville, Thor Park 8320, B-3600 Genk, Belgium

!!↘ S-3p Cu-3d S-3p Cu-3d Sn-5s S-3p Sn-5p S-3p S-3p Cu-3d S-3p Cu-3d Si-3p S-3p S-3p Cu-3d S-3p Cu-3d Ge-4s S-3p Ge-4p S-3p

Cu

2

ZnSnS

4

Cu

2

ZnGeS

4

Cu

2

ZnSiS

4

In a nutshell

Insights of Sn substitution by Ge and Si in S-kesterite compounds

using DFT approach

Solar cell modelling

Correlation between non-radiative recombination rate and

solar cell characteristics

𝑅_!"#$ = 𝑅_"#$(1 − 𝑄%) 𝑄_%

Fig. 1: Cell efficiency with respect to the absorber layer thickness

Fig. 2: Cell efficiency with respect to 𝑄! for

an optimal absorber thickness value

à

_{Structural properties}

:

Materials 𝑬𝑮 [𝒆𝑽] 𝑸𝒊 𝑱_𝑺𝑪 [𝒎𝑨𝒄𝒎+𝟐] 𝑽_𝑶𝑪 [𝑽] 𝜼 [%] CZTS 1.32 1 27.68 1.06 25.88 10-4 _27.19 _0.70 _15.88 CZGS 1.89 1 13.54 1.58 19.94 10-4 _13.45 _1.22 _14.98 CZSS 3.06 1 1.24 2.67 3.11 10-4 _1.23 _2.31 _2.66 !!↘ !!↘ !!↘

à

_{Electronic properties}

:

à

_{Optical properties:}

Kesterite lattice contraction

Significant bandgap increase and slight increase of 𝑚∗

Absorption coefficients of the order of 104 _cm-1

𝛼 𝐸

, 𝑛(𝐸),

𝑅 𝐸

𝐴 𝐸 = 1 − 𝑅 exp(−2𝛼𝑑)

𝑅

_!"#

(𝑛), 𝑅

_$!"#

(𝑄

_%

, 𝑅

_!"#

)

𝜂, 𝐽

_&'

, 𝑉

_('

, 𝐹𝐹

Improved Shockley-Queisser model[1]

DFT input data: Model param.:

𝑇 = 300𝐾,

𝑑

[1] Blank et al., Phys. Rev. App., 8(2), 024032 (2017)

𝜂(𝑑, 𝑄

_%

)

Fig.1

𝑑

)*+

(𝑄

%

)

𝜂 𝑄

_%

:

#!"#

Fig.2

Modelling of the non-radiative recombination rate via an external parameter: 𝑄%

• _{Optimal absorber layer thicknesses} between 1.15 and 2.68 𝜇𝑚

• _{Disparity between the Si and the two other compounds in the reported cell} efficiencies due to 𝐽/0 limitations

• _{Distinguishable behaviour between 𝑅}_!"#$ = 0 𝑄_% = 1 _{and 𝑅}_!"#$ > 0 (𝑄_% < 1) _with respect to the absorber thickness 𝑑

• _{Decrease of the cell efficiency taking into account the} materials reflectivity

• _{The kesterite absorptance fixes the absolute efficiency loss} with respect to 𝑄% (Fig. 2)

• From Sn to Si kesterite, 𝜂 _{decreases explained by the 𝐽}/0 drop

not compensated by the increase of 𝑉10 (Fig. 3)

Fig. 3: JV cruves for 𝑑 = 1.5 𝜇𝑚 with respect to 𝑄!

Methodology:

• _{Possible efficiency imrpovement of 10% (CZTS) and 4.96%} (CZGS) via the reduction of 𝑅!"#$

• _{With higher bandgap and interesting efficiencies, CZGS} could be used in tandem approach

• _{CZSS might be implemented for PW windows} Submitted to Solar Energy Materials