Imaging physical parameters of pre‐breakdown Sites by lock‐in thermography techniques

Self Cite

We study the emission of light from industrial multicrystalline silicon solar cells under forward and reverse biases. Camera-based luminescence imaging techniques and dark lock-in thermography are used to gain information about the spatial distribution and the energy dissipation at pre-breakdown sites frequently found in multicrystalline silicon solar cells. The pre-breakdown occurs at specific sites and is associated with an increase in temperature and the emission of visible light under reverse bias. Moreover, additional light emission is found in some regions in the subband-gap range between 1400 and 1700 nm under forward bias. Investigations of multicrystalline silicon solar cells with different interstitial oxygen concentrations and with an electron microscopic analysis suggest that the local light emission in these areas is directly related to clusters of oxygen.

Section: Figmentioning

confidence: 94%

Luminescence emission from forward- and reverse-biased multicrystalline silicon solar cells

Bothe

Ramspeck

Hinken

et al. 2009

Self Cite

“…Note that both the early breakdown (type 1) and the defect-induced breakdown (type 2) show a negative or close to zero TC in TC-DLIT images. 12,22 However, in addition to breakdown types 1, 2, and 3, there are other current contributions which have not been discussed yet. One is the edge current, which flows at the edge of the cells where the p-n junction plane reaches the surface.…”

Section: Discussionmentioning

confidence: 99%

“…For the investigation of breakdown phenomena in solar cells, special LIT techniques have been developed for imaging different physical properties of breakdown sites quantitatively. 12 By evaluating LIT images taken in the dark (DLIT) at different temperatures and biases, images of the temperature coefficient (TC, given in % current change per K) of the local currents and of the relative slope of the local I-V characteristics (given in % current change per V) may be obtained. Since these parameters are normalized to the total current values, they are not influenced by the magnitude of the individual local breakdown currents but generally characterize the underlying breakdown mechanism.…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Understanding junction breakdown in multicrystalline solar cells

Breitenstein

Bauer

Bothe

et al. 2011

123

Extensive investigations on industrial multicrystalline silicon solar cells have shown that, for standard 1 X cm material, acid-etched texturization, and in absence of strong ohmic shunts, there are three different types of breakdown appearing in different reverse bias ranges. Between À4 and À9 V there is early breakdown (type 1), which is due to Al contamination of the surface. Between À9 and À13 V defect-induced breakdown (type 2) dominates, which is due to metal-containing precipitates lying within recombination-active grain boundaries. Beyond À13 V we may find in addition avalanche breakdown (type 3) at etch pits, which is characterized by a steep slope of the I-V characteristic, avalanche carrier multiplication by impact ionization, and a negative temperature coefficient of the reverse current. If instead of acid-etching alkaline-etching is used, all these breakdown classes also appear, but their onset voltage is enlarged by several volts. Also for cells made from upgraded metallurgical grade material these classes can be distinguished. However, due to the higher net doping concentration of this material, their onset voltage is considerably reduced here.

“…Therefore, intense research into the reasons and the physical understanding of breakdown were undertaken, especially for (multi-) crystalline silicon solar cells. [1][2][3][4][5][6][7][8] Like in other silicon-based electronic devices, breakdown causes the emission of visible light, the reverse biased electroluminescence (ReBEL). 9,10 It is therefore possible to investigate and locate the occurring high currents not only with (Lock-in) thermography 2 (LIT) but also with CCD cameras offering higher spatial resolution.…”

mentioning

confidence: 99%

Electric properties and carrier multiplication in breakdown sites in multi-crystalline silicon solar cells

Schneemann

Kirchartz

Carius

et al. 2015

This paper studies the effective electrical size and carrier multiplication of breakdown sites in multi-crystalline silicon solar cells. The local series resistance limits the current of each breakdown site and is thereby linearizing the current-voltage characteristic. This fact allows the estimation of the effective electrical diameters to be as low as 100 nm. Using a laser beam induced current (LBIC) measurement with a high spatial resolution, we find carrier multiplication factors on the order of 30 (Zener-type breakdown) and 100 (avalanche breakdown) as new lower limits. Hence, we prove that also the so-called Zener-type breakdown is followed by avalanche multiplication. We explain that previous measurements of the carrier multiplication using thermography yield results higher than unity, only if the spatial defect density is high enough, and the illumination intensity is lower than what was used for the LBIC method. The individual series resistances of the breakdown sites limit the current through these breakdown sites. Therefore, the measured multiplication factors depend on the applied voltage as well as on the injected photocurrent. Both dependencies are successfully simulated using a series-resistance-limited diode model.