An Evaluation of Constituents in Paste for Silicon Solar Cells with Floating Contact Method: A Case Study of Tellurium Oxide

Transcription

1 7 th Metallization Workshop, Konstanz, Germany, 2017 An Evaluation of Constituents in Paste for Silicon Solar Cells with Floating Contact Method: A Case Study of Tellurium Oxide Takayuki Aoyama 1, 2, Mari Aoki 3, 4, Isao Sumita 3,4, Yasushi Yoshino 1, Atsushi Ogura 2 1 Noritake Co., Limited 2 Meiji University 3 Asada Mesh Co., Ltd. 4 Toyota technological Institute Corresponding author: takayuki_aoyama@n.noritake.co.jp

2 Outline Motivation - Problems in contacts Evaluation method - Floating contact method Case study 1 - Effects of paste constituents on n-type solar cells Case study2 - Impacts of TeO 2 on Ag paste in conventional p-type solar cells Conclusion 7 th Metallization Workshop, Konstanz, Germany, / 22

3 Problems in contacts Recombination Shunting Severe limit of cell efficiency! High V oc Loss in V oc Cell V oc implied V oc Smaller contact area (e.g., PERC, PERL) M. Green et al., (1986, May, 20), US Patent Lower shunting and recombination Paste contacts Ag metal Glass frit Additives??? Shunting Recombination Metallization area fraction A. Edler et al., Prog. Photovolt., 23, 620, Effects of each constituent on cell performance should be clarified. 7 th Metallization Workshop, Konstanz, Germany, / 22

4 Floating contact method Standard H-pattern grid-contact An electrode to measure cell parameters Ag Paste used is fixed through experiments. Floating contacts (F.C.) interpose between adjacent fingers.* Electrically and geometrically isolated from grid-contact Less influences on measuring cell parameters Affecting on carrier behavior: shunting or recombination Test pastes used Conductive Nonconductive Non-contact This method can clearly show paste effects on shunting and recombination. R. Hoenig, Ph. D. dissertation, th Metallization Workshop, Konstanz, Germany, / 22

5 7 th Metallization Workshop, Konstanz, Germany, / 22 Floating contact method Floating contact area fraction Increasing 0% 4% 8% 12% grid One F.C Two F.C. Three F.C. busbar Contact area fraction depending on the number of F.C.

6 7 th Metallization Workshop, Konstanz, Germany, / 22 Case study 1 Effects of paste constituents on n-type solar cells

7 7 th Metallization Workshop, Konstanz, Germany, / 22 Experimental setup SiN x /SiO 2 p + emitter (70Ω/sq.) n + BSF (40Ω/sq.) Ag paste Grid-contact: Ag/Al paste n-type Si (156 x156 mm 2 ) Floating contacts: homemade test pastes Ag-only paste Ag No glass frit Ag/glass paste Ag/glass/Al paste glass Ag glass Ag Al Glass frit: PbO-SiO 2 -B 2 O 3 -ZnO Effects of Al T. Aoyama et al., Energy Procedia, vol. 98, pp.106, 2016

8 Dark I-V curves Current density (ma/cm 2 ) Hump current Ag/glass Ag-only Grid-contact only Applied voltage (V) Glass frit in the Ag paste significantly increases the hump current due to shunt and/or recombination current. 7 th Metallization Workshop, Konstanz, Germany, / 22

9 Dark I-V curves Current density (ma/cm 2 ) Hump current Ag/glass Ag/glass/Al Ag-only Grid-contact only Applied voltage (V) The hump current decreases by adding Al to the Ag/glass paste. This method demonstrates mitigation effect of Al in the Ag/Al paste. 7 th Metallization Workshop, Konstanz, Germany, / 22

10 7 th Metallization Workshop, Konstanz, Germany, / 22 Experimental setup This method can even evaluate insulating materials like glass frit. SiN x /SiO 2 p + emitter (70Ω/sq.) n + BSF (40Ω/sq.) Ag paste Grid-contact: Ag/Al paste n-type Si (156 x156 mm 2 ) Floating contacts: homemade test pastes Glass frit paste glass Effects of glass frit itself * Glass/Al paste glass Al Effects of Al on glass frit Glass frit: PbO-SiO 2 -B 2 O 3 -ZnO *T. Aoyama et al., IEEE J. Photovolt., Vol. 7, No. 5, p. 1313, 2017.

11 Dark I-V curves Current density (ma/cm 2 ) Glass Ag/glass Ag/glass/Al Ag-only Grid-contact only Applied voltage (V) Glass frit itself drastically increases the hump current. 7 th Metallization Workshop, Konstanz, Germany, / 22

12 Dark I-V curves Current density (ma/cm 2 ) Glass Glass/Al Ag/glass Ag/glass/Al Ag-only Grid-contact only Applied voltage (V) The hump current also reduces by adding Al to the glass frit paste, as in the case of the Ag/glass paste. 7 th Metallization Workshop, Konstanz, Germany, / 22

13 7 th Metallization Workshop, Konstanz, Germany, / 22 Analysis results of dark I-V curves; R sh,j 02 Numerical Fitting with the two-diode model Shunt resistance R sh (Ωcm 2 ) Ag-only Ag/glass/Al Glass frit Glass/Al Ag/glass Floating contact fraction (%) Recombination current density J 02 (A/cm 2 ) Glass frit Glass/Al Ag/glass Ag/glass/Al Ag-only Floating contact fraction (%) The Floating contact method clearly shows the dependence of R sh and J 02 on the fraction every pastes. Simplifying these results

14 7 th Metallization Workshop, Konstanz, Germany, / 22 Analysis results of dark I-V curves; R sh,j Ag-only Ag/glass/Al R sh (Ωcm) glass Degradation Mitigation Al Ag/glass Glass/Al Glass-only Al Mitigation Degradation J 02 (A/cm 2 ) Aluminum addition to glass frit paste reduces the J 02 increase Aluminum addition to Ag/glass paste reduces both of the R sh decrease and the J 02 increase.

15 7 th Metallization Workshop, Konstanz, Germany, / 22 Summary Aluminum can mitigate the recombination current increase not only in the silver/aluminum paste, but also in the glass frit paste. The floating contact method can demonstrate the effects of the paste constituents on shunting and recombination in the n-type solar cells.

16 7 th Metallization Workshop, Konstanz, Germany, / 22 Case study 2 Impact of TeO 2 addition on Ag paste in conventional p-type solar cells Background TeO 2 is used as a constituent of glass frit in almost commercially available Ag paste to achieve high-efficiency of silicon solar cells. Detail effects of the TeO 2 on the Ag paste has not been clarified yet.

17 Experimental setup n + emitter (80Ω/sq.) Al BSF SiN x Grid contact: Ag paste p-type Si (156 x156 mm 2 ) Al paste Floating contacts: homemade test pastes Ag-only paste Ag/glass paste Ag/glass/TeO 2 paste Ag glass Ag glass Ag TeO 2 No glass frit Glass frit: PbO-SiO 2 -B 2 O 3 -ZnO Effects of TeO 2 7 th Metallization Workshop, Konstanz, Germany, / 22

18 Effects of TeO 2 on dark I-V curves Current density (ma/cm 2 ) Hump current Ag/glass Ag-only Grid-contact only Applied voltage (V) Glass frit in the Ag/glass paste significantly increases the hump current due to shunt and/or recombination current. 7 th Metallization Workshop, Konstanz, Germany, / 22

19 Effects of TeO 2 on dark I-V curves Current density (ma/cm 2 ) Hump current Ag/glass Ag-only Ag/glass/TeO 2 Grid-contact only Applied voltage (V) Increasing rate of the hump current on the Ag/glass paste is reduced by the TeO 2 addition to the paste. 7 th Metallization Workshop, Konstanz, Germany, / 22

20 Effects of TeO 2 on shunt resistance Shunt resistance R sh (Ωcm 2 ) Ag/glass/TeO 2 Ag-only Grid-contact only Ag/glass Floating contact fraction (%) The R sh decreasing rate of Ag/glass paste reduces by adding TeO 2 to Ag/glass paste. 7 th Metallization Workshop, Konstanz, Germany, / 22

21 Effects of TeO 2 on recombination current Recombination current density J 02 (A/cm 2 ) Ag/glass Ag/glass/TeO 2 Ag-only Grid-contact only Floating contact fraction (%) The J 02 increasing rate of Ag/glass paste drastically reduces by adding TeO 2 to Ag/glass paste. 7 th Metallization Workshop, Konstanz, Germany, / 22

22 Summary TeO 2 in Ag paste reduces R sh decreasing rate and J 02 increasing rate in conventional p-type solar cells. The floating contact method can clarify effects of paste constituents on shunting and recombination not only in n- type solar cells, but also in conventional p-type solar cells. 7 th Metallization Workshop, Konstanz, Germany, / 22

23 Conclusion The effects of paste constituents on shunting and recombination were clarified in the following case studies: Al effects on Ag paste in n-type solar cells Effects of glass frit itself in n-type solar cells Al effects on glass frit itself in n-type solar cells TeO 2 effects on Ag paste in conventional p-type solar cells The floating contact method is a very effective and powerful tool to evaluate paste and/or paste constituents for development of high efficiency solar cells. 7 th Metallization Workshop, Konstanz, Germany, / 22

24 We are looking forward to understanding the mechanism of the effects of paste on shunting and recombination underneath the metallization contacts, and to innovate a new composition of paste for high efficiency cells by using the floating contact method. Thank you for your kind attention! 7 th Metallization Workshop, Konstanz, Germany, 2017