Rahul Dewan - Jacobs University

6.2. Results and Discussion
mA/cm 2
(a)
(b)
(c)
Figure 6.5: Short circuit current for a 1-µm-thick microcrystalline silicon solar cell as a
function of the grating period and height illuminated under (a) blue light (wavelength
300 – 500 nm), (b) red and infrared light (wavelength 700 – 1100 nm), and (c) entire
sun spectrum (wavelength 300 – 1100 nm). The set of figures show the behavior of
solar cells with triangular grating.
of around 1 mA/cm 2 is observed. This enhancement of the short circuit current is
observed for grating periods smaller than 300 nm. Since the period of the grating is
smaller than the incident wavelength, the grating acts as an effective refractive index
gradient. The graded refractive index acts as a matching layer between the refractive
index of zinc oxide and microcrystalline silicon. For grating periods larger than the
incident wavelengths (period > 1 µm), the short circuit current drops as well. Light
is only diffracted at small diffraction angles, which can be explained using the grating
equation (Eq. 4.7 on page 55). Henceforth, the diffracted light does not interfere with
diffracted light from neighboring unit cells. The intensity profile essentially becomes
a superposition of absorption pattern arising from a flat solar cell and that from the
grating of the unit cell. Thus, the short circuit current for such large grating periods
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