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EL inspection for different PV technologies.

D. Martinez Biro

The following report shows the results of the imaging taken on the 31/07/14 in the TUDelft. The amount

of defects that was possible to identify was higher than the previous measurement day. Also a wider

variety of technologies was available.

Crystalline Silicon

Single Crystalline Silicon

12 cells panel (30W).

A small panel with a capacity of 30W was used to perform EL imaging. The results presented below where

obtained when applying two different current levels. Note that the top left cell from the panel that was

under a lower current was covered with a cardboard at the moment of the measurement. It can also be

noted that noise is more present in the image where a lower current was being used.

Defects found:

-

Broken fingers

-

Furnace belt burn.

-

Crack: Partial and full interruption.

-

Unequal cell quality.

-

Possible short circuit

Figure 1 21V / 0.48A Figure 2 23.4V / 2.01A

88 cells panel, back contacts only (327W).

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When doing the measurements for this panel it could be observed that it was the brightest. The camera

sensitivity was higher for the photon wavelength emitted by this panel. If a normal exposure of 30 seconds

was used, as in the rest of the panels, the image would appear almost completely white. Exposure time

was reduced to 2 seconds to be able to obtain images visible enough to analyze.

Unequal cell quality.

Defects found:

-

Micro crack.

-

Short circuit.

-

Unidentified darker line.

-

One cell not working.

Figure 3 sc-Si, 6A / 71 V. Back contacts only.

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Figure 4 sc-Si, 3A / 67 V. Back contacts only, no tent.

Figure 5 sc-Si, 3A / 67 V. Back contacts only, no tent.

The last two images were taken without using the tent and a clear enough image was obtained. This same

set was not tried with the rest of the panels but it will be considered for further measurements. In figure

5 it can be seen one dark cell, this can be caused by a connection interruption.

Poly Crystalline Silicon

Metal Web Through

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Defects found:

-

Uneven cell quality.

-

Micro cracks.

Figure 6 MWT, 2A.

Figure 7 MWT, 4A.

Thin Film

CdTe

Low currents forward biased to the panel were used (~0.05A), no results were obtained. A darker section

on the panel was identified, this section was also present in the previous EL imaging done in this type of

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panel. As this panel has been under more aging factors, this dark area cis bigger. It could also be seen that

low currents allow shunt resistances to show higher effect because of higher contrast in comparison with

the rest of the panel, even though, in order to obtain a more punctual location of the shunt path, it is

better to apply a higher current. This can be seen in the images below.

Defects found:

-

Uneven cell quality distribution.

-

Shunt resistances.

Figure 8 CdTe, 60.0V/0.5A, 90V/1A, and 97V/2A, respectively from left to right.

CIS

The defects found in the CIS panel were very similar to the ones in the CdTe panel, the effect of the current

on the shunt resistances was repeated. A more even cell quality can be observed in this panel compared

to the CdTe.

Defects found:

-

Shunt resistances.

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Figure 90.62A/43V, 1.25A/46V, and 2.5A/49.3V, respectively from left to right.