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Suppressing lossy-film-induced angular mismatches between reflectance and transmittance extrema: optimum optical designs of interlayers and AR coating for maximum transmittance into active layers of CIGS solar cells

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Abstract

The investigation of optimum optical designs of interlayers and antireflection (AR) coating for achieving maximum average transmittance (Tave) into the CuIn1−xGaxSe2 (CIGS) absorber of a typical CIGS solar cell through the suppression of lossy-film-induced angular mismatches is described. Simulated-annealing algorithm incorporated with rigorous electromagnetic transmission-line network approach is applied with criteria of minimum average reflectance (Rave) from the cell surface or maximum Tave into the CIGS absorber. In the presence of one MgF2 coating, difference in Rave associated with optimum designs based upon the two distinct criteria is only 0.3% under broadband and nearly omnidirectional incidence; however, their corresponding Tave values could be up to 14.34% apart. Significant Tave improvements associated with the maximum-Tave-based design are found mainly in the mid to longer wavelengths and are attributed to the largest suppression of lossy-film-induced angular mismatches over the entire CIGS absorption spectrum. Maximum-Tave-based designs with a MgF2 coating optimized under extreme deficiency of angular information is shown, as opposed to their minimum-Rave-based counterparts, to be highly robust to omnidirectional incidence.

© 2014 Optical Society of America

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Figures (6)

Fig. 1
Fig. 1 The structure considered in this work: (a) a typical CIGS solar cell with a MgF2 AR coating on soda-lime glass and (b) the associated rigorous transmission-line network representation of two adjacent layers within the cell, where κ = α + and Z0 represent the complex propagation constant and the characteristic impedance, respectively.
Fig. 2
Fig. 2 Polarization-averaged reflectance R(λ, θ) obtained based on criteria of minimum average reflectance (a) and maximum average transmittance (b) for a typical CIGS solar cell.
Fig. 3
Fig. 3 Polarization-averaged transmittance T(λ, θ) obtained based on criteria of minimum average reflectance (a) and maximum average transmittance (b) for a typical CIGS solar cell.
Fig. 4
Fig. 4 Comparisons between the angle-averaged reflectance (a) and transmittance (b) associated with SA-optimized MgF2/interlayer thicknesses based on minimum average reflectance CR() and maximum average transmittance CT () criteria.
Fig. 5
Fig. 5 Comparisons in angular mismatch spectra among some CIGS solar cell designs: (a) based on minimum average reflectance, CR(), (b) based on maximum average transmittance, CT (), and (c) by setting the interlayer thicknesses to their respective minima [(t AZO, t ZnO, t CdS) = (150, 40, 40) nm].
Fig. 6
Fig. 6 Robustness studies of the structure to broadband and nearly-omnidirectional incidence when it was optimized at a single incident angle based on cost function CT () or CR(): (a) the average reflectance Rave, and (b) the average transmittance Tave. Quantities Rave and Tave were averaged over the TE/TM, λ = [350, 1200] nm, and θ = [0°, 80°]. The horizontal axis represents the incident angle at which the optimization is conducted.

Tables (3)

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Table 1 Domains of Variables of the Cost Function Ci(), i = {R, T}, Used in Simulated-Annealing Optimizations.

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Table 2 Performance and Layer Thickness (in nm) Comparisons between SA-Optimized Results Based on Minimum Average Reflectance [CR(), Eq. (3)] and Maximum Average Transmittance [CT (), Eq. (4)] Criteria, All without Solar Spectrum Weighting (SSW), for a Typical CIGS Solar Cell.

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Table 3 Performance and Layer Thickness (in nm) Comparisons between SA-Optimized Results Obtained Based on Minimum Average Reflectance [CR(), Eq. (3)] and Maximum Average Transmittance [CT (), Eq. (4)] Criteria, All without Solar Spectrum Weighting (SSW), for a Typical CIGS Solar Cell under Normal Incidence.

Equations (4)

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V 0 , i + 1 + = { 2 ( R 0 , i 2 + X 0 , i 2 ) 1 / 2 P in , i [ R 0 , i ( e + 2 α i t i | Γ i + 1 | 2 e 2 α i t i ) 2 X 0 , i | Γ i + 1 | sin ( ϕ i + 1 2 β i t i ) ] } 1 / 2 ,
P in , i + 1 ( z = 0 ) = 1 2 Re [ | V 0 , i + 1 + | 2 Z 0 , i * ( 1 Γ i + 1 * + Γ i + 1 | Γ i + 1 | 2 ) ]
C R ( X _ ) = Δ θ Δ λ [ | Γ TE ( X _ , λ , θ ) | 2 + | Γ TM ( X _ , λ , θ ) | 2 ] I ( λ ) d λ d θ 2 Δ θ Δ λ I ( λ ) d λ d θ ,
C T ( X _ ) = 1 Δ θ Δ λ [ T TE ( X _ , λ , θ ) + T TM ( X _ , λ , θ ) ] I ( λ ) d λ d θ 2 Δ θ Δ λ I ( λ ) d λ d θ ,
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