TITLE:
Optimizing a CIGS Thin-Film Solar Cell with SILVACO ATLAS: Effects of Optical Bandgap and Absorber Electron Affinity
AUTHORS:
Alioune Ngom, Youssou Gning, Mamadou Lamine Samb, Aly Toure, Moussa Toure, Ahmed Mohamed-Yahya
KEYWORDS:
CIGS Thin-Film Solar Cells, Optical Bandgap, Electron Affinity, Band Alignment (CdS/CIGS), Open-Circuit Voltage, Fill Factor, Power-Conversion Efficiency
JOURNAL NAME:
Journal of Materials Science and Chemical Engineering,
Vol.13 No.10,
October
16,
2025
ABSTRACT: This study uses TCAD numerical simulation to evaluate how key absorber parameters in Cu(In, Ga)Se2 (CIGS) thin-film solar cells influence device performance, with the objective of identifying low-material, cost-effective optimization strategies. While crystalline-silicon (c-Si) still dominates the market despite its indirect bandgap and the thick wafers it requires, the CIGS pathway, featuring a direct, composition-tunable bandgap and a high absorption coefficient, on glass or flexible polymer substrates, offers a compelling alternative. The device investigated adopts the stack Al/ZnO/CdS/CIGS/Mo/PET and is simulated in SILVACO ATLAS (drift-diffusion transport coupled to Poisson and carrier-continuity equations) under conditions close to STC (AM1.5G, 27˚C, 1000 W·m−2). Parameter sweeps cover the absorber optical bandgap
g∈[
1.14, 1.50 ]
eV, electron affinity
χ∈[
4.0, 4.8 ]
eV, and CIGS thickness
d∈[
0.1, 3.0 ]
μm, with p-type doping fixed at 1 × 1016 cm−3. The results show that the short-circuit current density
J
sc
is nearly invariant with respect to
E
g
and
χ
once the absorber is sufficiently thick (
d≥0.3 μm
); a deviation appears at
d=0.1 μm
, attributed to stronger optical losses (residual transmission) and less efficient carrier collection. In contrast, the open-circuit voltage
V
oc
increases markedly with
E
g
over the investigated range (consistent with a reduced effective saturation current), which in turn raises the fill factor
FF
and the power-conversion efficiency η. The electron affinity
χ
has little influence on
J
sc
(except for
d<0.3 μm
), but it systematically impacts
V
oc
,
FF
, and η\etaη via band alignment at the buffer/absorber interface. Within our parameter window, a maximum efficiency of about 27.05% is achieved for
E
g
≈1.50 eV
with
d=3.0 μm
, where gains in
V
oc
and
FF
compensate the near-invariance of
J
sc
. Moreover, electron-affinity windows of
χ≈4.0 - 4.2 eV
and
χ≈4.6 - 4.8 eV
are shown to be favorable across 0.1 - 3.0 μm. These findings suggest that joint engineering of composition (Ga content) to tailor
E
g
and of band alignment (through
χ
and the CdS/CIGS/ZnO interfaces) is a robust route to boost CIGS efficiency while minimizing material usage.