4 Solar Cells: Optical and Recombination Losses
85
a
b
Fig. 4.9 Surface of a monocrystalline wafer after texturing a side view; b top view. Courtesy Meyer
Burger Technology AG
pyramids with a size of 1–7 μm can be etched out at an angle of ∼35° to the vertical
axis. Figure 4.9 shows the surface of a monocrystalline, textured wafer.
With a refractive index for the ARC layer of 2, we obtain a refraction angle of
24°, if we solve (4.9) for β 2
n 1 × sin(β 1 ) = n 2 × sin(β 2 ) → β 2 = arcsin(n 1 /n 2 × sin(β 2 ))
= arcsin(0.5 sin(55
◦
)) = 24
◦
(4.11)
with:
n 1 Refractive index of air ≈ 1
n 2 Refractive index of ARC ≈ 2
β 1 Angles of the pyramids in the textured layers to the vertical:
70.5
◦
/2 ≈ 35
◦
β 1 = 90
◦
− 35
◦
= 55
◦
β 2 Refraction angle of ARC
Vertically incident light strikes the pyramidal texture at an angle of 35° (resp 55°)
(see Fig. 4.10). The first part 1 namely about 30%, is reflected, also at 35° (angle
of incidence = angle of reflection) and impinges on an adjacent pyramid, whereas
the second part 2, namely 70%, is refracted into the antireflexion coating (ARC) at
an angle of ~24° and then enters the solar cell at an angle of ~12°. The light that is
refracted is, in the ideal case, thrown back into the solar cell from the back side and
hits the texture from below. In this way, the optical length of the light is increased
and with it, the probability of generating electron-hole pairs.
For multicrystalline wafers, pyramids cannot be etched because the crystal structure is not aligned, as in a monocrystal. Attacking and roughening the surface with
85
a
b
Fig. 4.9 Surface of a monocrystalline wafer after texturing a side view; b top view. Courtesy Meyer
Burger Technology AG
pyramids with a size of 1–7 μm can be etched out at an angle of ∼35° to the vertical
axis. Figure 4.9 shows the surface of a monocrystalline, textured wafer.
With a refractive index for the ARC layer of 2, we obtain a refraction angle of
24°, if we solve (4.9) for β 2
n 1 × sin(β 1 ) = n 2 × sin(β 2 ) → β 2 = arcsin(n 1 /n 2 × sin(β 2 ))
= arcsin(0.5 sin(55
◦
)) = 24
◦
(4.11)
with:
n 1 Refractive index of air ≈ 1
n 2 Refractive index of ARC ≈ 2
β 1 Angles of the pyramids in the textured layers to the vertical:
70.5
◦
/2 ≈ 35
◦
β 1 = 90
◦
− 35
◦
= 55
◦
β 2 Refraction angle of ARC
Vertically incident light strikes the pyramidal texture at an angle of 35° (resp 55°)
(see Fig. 4.10). The first part 1 namely about 30%, is reflected, also at 35° (angle
of incidence = angle of reflection) and impinges on an adjacent pyramid, whereas
the second part 2, namely 70%, is refracted into the antireflexion coating (ARC) at
an angle of ~24° and then enters the solar cell at an angle of ~12°. The light that is
refracted is, in the ideal case, thrown back into the solar cell from the back side and
hits the texture from below. In this way, the optical length of the light is increased
and with it, the probability of generating electron-hole pairs.
For multicrystalline wafers, pyramids cannot be etched because the crystal structure is not aligned, as in a monocrystal. Attacking and roughening the surface with