REPORTERS: SEPTIA KHOLIMATUSSA’DIAHCO-WORKER: CHENG-YING CHEN

Appl. Phys. Lett. 104, 051105 (2014)

Enhancing the Cu2ZnSnS4 solar cell efficiency by back contact modification: inserting a

thin TiB2 intermediate layer at Cu2ZnSnS4/Mo interface

+ Earth abundant and non-toxic elements

+ Low cost+ Direct tunable

band gap of 1.0 ~ 1.5 eV

+ Large absorption coefficient of 104 cm-1

+ Work function of 4.6 eV

Cu2ZnSn(S,Se)4 (CZTS)

Cu Zn Sn S

TiB2 (Titanium Diboride)

+ Refractory intermetallic compound

+ High melting point of 3225 °C

+ High electrical conductivity of ~105 S/cm

+ High work function of 5.08 eV

+ Chemical stability

EXPERIMENT

TiB2 layer: RF sputteringCZTS layer: sol-gel route then sulfurization

CdS (80 nm): CBD

ZnO (60 nm): RF sputteringZnO:Al (500 nm): DC sputtering

Ni-Al: thermal evaporation

SEM RESULTS

(a) Without the TiB2 layer; (b) with 30 nm TiB2 layer

(c) Without the TiB2 intermediate layer, inset: EDS line scan taken along the arrow direction

TEM RESULTS

(d) With 30 nm TiB2 intermediate layer, inset: EDS line scan taken along the arrow direction

Note: due to the overlap of S-Kα and Mo-Lα peaks in EDS, the S distribution actually is the combination of Mo and S while Mo-Kα peak only belongs to Mo.

RAMAN RESULTS

MoS2

XRD patterns and Raman spectra of CZTS on Mo back contact with TiB2

layers.

CZTS

CZTSMoS2

J-V CHARACTERISTICS

1. The efficiency raises from 3.06% to 4.40% by inserting 30 nm TiB2 layer.

2. The Jsc and FF of 70 nm TiB2 layer decreases from 13.21 to 13.08 and 0.56 to 0.54 in compared with 30 nm TiB2 layer.

3. TiB2 layer can inhibit the formation of MoS2 layer, so the device efficiency can be improved. But it would degrade the CZTS crystallinity.

SUMMARY

Material

Ф(eV)

CZTS/CIGS

Eff.(%)

Jsc(mA/cm2)

Voc(mV)

FF(%)

Rs(Ω.cm2)

Thickness

(nm)Function Ref.

TiB2 5.08 CZTS‡ 4.40 13.21 598 56 10.3 30† DB 1

ZnO 4.71

CZTS† 4.3 15.97 641 42 15.1 10† DB 2

CZTSe† 6.0 28.6 364 57.5 <0.1 10† DB 3

CIGSe* 10.04 31.16 500 64 - 3000† DB 4

TiN 4.7CZTSe* 8.9 42.6 385 54.2 1.8 20* DB 5

CZTS† 5.5 18.7 621 47.1 6.9 20† DB 6

ZrN 4.6 CIGSe* 10.4 25.4 580 70.5 0.69 1000† R 7

Ag 4.26 CZTS† 4.42 15.05 597.7 49.2 12.8 20* DB 8

PERFORMANCE OF CZTS/CIGS SOLAR CELL WITH VARIOUS BACK CONTACT MATERIALS MODIFICATION

Reference:1. Appl. Phys. Lett. 104, 051105 (2014)2. Phys. Status Solidi RRL, 1-5 (2014)3. J. Mater. Chem. A, 2013, 1, 8338-83434. Solar Erg. Mater. & Solar Cells 93 (2009) 654-656

5. Appl. Phys. Lett. 101, 053903 (2012)6. Chem. Mater. 2013, 25, 3162-31717. Appl. Phys. Lett. 85, 2634 (2004)8. Appl. Phys. Lett. 104, 041115 (2014)

DB=diffusion barrier R=back reflectorDeposition method: † sputtering * thermal evaporation ‡ solution process

Potential Materials for Back Contact Modification as Diffusion Barrier: Pt, Au, V(S/Se), Ta(S/Se), Nb(S/Se), Sn(S/Se), W(S/Se), Zr(S/Se), Ti(S/Se), Hf(S/Se),

Ga(S/Se), In(S/Se), Al(S/Se)

Future Work1. TiSe2, Ф = 5.6 eV

ref.: Thin Solid Films 431-432 (2003) 382-3862. HfSe2, Ф = 5.9 eV

ref.: Appl. Phys. Lett. 103, 053513 (2013)

THANK YOU