Supporting Information
Solution processed high band-gap CuInGaS2 thin film for
solar cell applications
Se Jin Park, Jin Woo Cho, Joong Kee Lee, Keeshik Shin, Ji-Hyun Kim and Byoung Koun Min*
Calculation of band-gap
The optical property of the CIGS film was also investigated by UV-Vis absorption
spectroscopy. As can be seen in Figure 2b, absorption showed below 900 nm. Since the
absorption coefficient α is related to the direct band-gap according to the below Equation (1),
the optical band-gap (Eg) can be determined by extrapolating the linear region of the plot
(αhv)2 versus hv and taking the intercept [1].
(ahv) 2  hv  Eg
(1)
In Equation (1) h is the Planck constant, and v is the radiation frequency. In this calculation
the absorption coefficient α was determined from Equation (2).
2


1  (1  R) 2
 (1  R) 2 
2 
  ln 
 

R


d  2T
 2T 



(2)
In this equation T is transmittance, R is reflectance, and d is sample thickness. The estimated
direct optical band-gap of the film is found to be 1.57±0.02 eV (Figure 2b).
The band-gap can be also calculated from the IPCE data using Equation (1) through the
evaluation of the absorption coefficient α from Equation (3), given by [2]
   ln(1  IPCE )
(3)
A band-gap of 1.53±0.01 eV was obtained (the inset of Figure 4b).
Figure S1. Thermal gravimetric analysis (TGA) of polyvinyl acetate and CIG paste film
Figure S2. Top-view SEM images of Cu, In, and Ga mixed oxide films prepared by the
pastes with PVA (a) and ethyl cellulose (b) as a binder material
Figure S3. Photoluminescence (PL) spectra of the CIGS film measured at 300 K (excitation
source of 355 nm). PL band maximum appears at 810 nm which corresponds to the band-gap
of 1.55 eV.
Table S1. Electrical properties of the CIGS film
Sample
Type
Carrier
concentration
(cm-3)
CIGS
p
9.4×1016
Mobility
(cm2/V·s)
Resistivity
(Ω·cm)
6.63
10
Figure S4. (a) Top-view SEM image of the CIGS film prepared by the pastes with ethyl
cellulose as a binder material and (b) the current density-voltage characteristics of the solar
cell device with the CIGS film shown in (a)
Reference
[1] Woo K, Kim Y, Moon J. A non-toxic, solution-processed, earth abundant absorbing layer
for thin-film solar cells. Energy & Environmental Science 2012; 5:5340-5345.
[2] Hegedus SS, Shafarman WN. Thin-film solar cells: Device measurements and analysis.
Progress in Photovoltaics: Research and Applications 2004; 12(2-3):155-176.