Modelling the effects of future improvements in metallization of solar cells

The proposed modelling of the series resistance constitutes a powerful tool to know how industrial solar cells can evolve thanks to the improvement of metallic pastes, or new passivation processing for bulk and surface. With this purpose the modelling will be used to evaluate the efficiency of a solar cell (with an optimal H-pattern grid design) when it
happens a change in the technological parameters related to the metallic contact (resistivity of metal and contact resistance) or in the Voc (parameter that is related to the passivation of volume and surfaces). All the rest of parameters of the modelling have been kept constant for this analysis with the values referred in Table 7.

L

156 mm

Jsc(without grid shadow)

36.5 mA/cm2

Number of bus-bars

2 and 3

Number of contacts per bus-bar

8

wbase

200 pm

Pbase

1 Qcm

wbus

2.45 mm (2 bus-bars) 1.85 mm (3 bus-bars)

wf

100 pm

hbus

25 pm

hf

12 pm

Re

45 Q/sqr

Table 7. Model parameters used in the analysis of the evolution of the cell behaviour when the technological parameters associated to the screen-printing technology are modified

Results of the modelling are plotted in Fig. 13 for two different situations, with a Voc of 616 mV and for a Voc of 630 mV.

image691

Fig. 13. Modelling results for the efficiency as a function of the finger resistivity and contact resistance for cells of two and three bus-bars with the optimal design of grid in each case, when generated current are kept constant and two different Voc are considered. Rest of parameters for the modelling are taken from Table 7

As it is shown in the figure a jump in Voc of 14mV has an stronger impact in cell efficiencies than any possible improvement in the material of the front metallic grid; even when it is use the resistivity of the pure silver (1.63 pQcm (Lide, 1974)) for the optimal grid.

When an increase in generated current is studied, as it is shown in the Fig. 14, a similar result is obtained, showing that although it is possible to improve the solar cell performance thanks to the pattern optimization and enhancement of the materials properties for the front grid contact, the improvement of the device design and materials under the front contact have a bigger importance in the road to the industrial solar cells improvement.

image692

Fig. 14. Modelling results for the efficiency as a function of the finger resistivity and contact resistance for cells of two and three bus-bars with the optimal design of grid in each case, when Voc are kept constant and two different generated current are considered (36.5 and 37.5 mA/cm2 without grid shadowing). Rest of parameters for the modelling are taken from Table 7

Updated: August 22, 2015 — 3:58 pm