Solar Cell Operation, Performance and Design Rules Light Trapping - PowerPoint PPT Presentation

Solar Cell Operation, Performance and Design Rules Light Trapping II - Anti-Reflection and Trapping Methods Week 3.3.5 Arno Smets

Parasitic losses = outside absorbing layers 2 Al Al Reflection 2 n+ N+ p-type 4 Transmission C-Si 4 P++ P++ Al

Parasitic losses = outside absorbing layers 2 Al Al Reflection 2 n+ N+ p-type C-Si P++ P++ Al

Snell’s Law n 1 n 2  i    n sin n sin 1 i 2 t  t     r i r

The Fresnel equation n 1 n 2     i n sin n sin 1 i 2 t     t  r i r

P- and S- polarization P-polarization S-polarization

Fresnel coefficients S-polarization P-polarization 2   2         n cos( ) n cos( ) n cos( ) n cos( )       1 t 2 i R 1 i 2 t   R      p    S   n cos( ) n cos( )   n cos( ) n cos( ) 1 t 2 i 1 i 2 t     T 1 R T 1 R S s p p

Reflection coefficient (n 1 < n 2 ) Brewster Angle 100 n 1 =1.0 80 n 2 =1.5 P-polarization R s , R p (%) S-polarization 60 40 20 0 0 20 40 60 80 Angle of Incidence  i ( o )

Reflection coefficient (n 1 > n 2 ) 100 n 1 =1.5 Total internal 80 n 2 =1.0 P-polarization R s , R p (%) reflection S-polarization 60 40 20 0 0 20 40 60 80 Angle of Incidence  i ( o )

Reflection coefficient (n 1 > n 2 ) 100 n 1 =1.5 Total internal 80 n 2 =1.0 P-polarization R s , R p (%) reflection  crit = 41.8 o S-polarization 60 40 20 0 0 20 40 60 80 Angle of Incidence  i ( o )

Reduction Front Reflection: n 0 n s  4 n n 2 ( n n )  0 s  T 0 s   R  0 s 2  0 s n n 2 ( n n ) 0 s 0 s

Reduction Front Reflection: n 0 n s R 0 s = 0.388 T 0 s = 0.612

Rayleigh film N 0 N 1 N s First order 4 n n 4 n n   0 s approximation 0 1 T T      0 s 01  2 2 n n n n 0 s 0 1  2 ( n n )  0 1 R  01 2 ( n n ) 0 1  2 ( n n )  1 s R  1 s 2 ( n n ) 1 s

10 Lower reflection coeff @ 500 nm For siliconand air: 0.8 Total Reflection  n n n 1 0 S 0.6    1 4 . 3 2 . 1 0.4 0.2 0.0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Refractive Index n 1 N 0 N s

N 0 =1 N s =4.3 air silicon 0  R s 0 . 388 0  T s 0 . 612 silicon Anti-reflection air N 1 =2.07 R eff  0 . 229 eff = 0.771 T

Interference:

Interference: constructive destructive Interference Interference =0 =

Interference: the anti-reflection coating  Destructive interference  d  =  4 n E i E r1 E r2 2

Macroscopic roughness (d>>  ) Path of light rays Incident light Are determined Reflected 36 By refraction. Reflected

Parasitic losses = outside absorbing layers Al Al n+ N+ p-type 4 Transmission C-Si 4 P++ P++ Al

Enhancement of Absorption path length in Thin Film Solar cells  i <  critical 0 i 0 i 0 i 0 i 0 i 0 i 0 i

100 80 Total internal Rs , Rp ( % ) 60 reflection 40 20 0 0 20 40 60 80 Angle of Incidence 0 i ( o )

Enhancement of Absorption path length in Thin Film Solar cells  i <  critical

Enhancement of Absorption path length in Thin Film Solar cells n 2 =1.5 SiO 2 n 1 =4.3 silicon SiO 2 n 2 =1.5

Enhancement of Absorption path length in Thin Film Solar cells N 2 =2.2 ZnO n 1 =4.3 silicon ZnO n 2 =2.2

Light management in solar cells L d Increasing the absorption path length

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Enhancement absorption pathlength textured surface ` a p-type