Effect of Aluminum in Metallization Paste on the Electrical Losses in Bifacial N-type Crystalline Silicon Solar Cells

Transcription

1 6 th Metallization Workshop, Konstanz, Germany, 2016 Effect of Aluminum in Metallization Paste on the Electrical Losses in Bifacial N-type Crystalline Silicon Solar Cells Takayuki Aoyama 1, 2, Mari Aoki 3, Isao Sumita 3, Yasushi Yoshino 1, Yoshio Ohshita 3, Atsushi Ogura 2 1 Noritake Co., Limited 2 Meiji University 3 Toyota technological Institute Corresponding author: takayuki_aoyama@n.noritake.co.jp

2 Motivation - Problems in metallization with paste - In the case of Ag/Al metallization for n-type solar cells - Conventional evaluation for pastes Evaluation method - Floating contact method Test pastes - Homemade three test pastes Aluminum effects on n-type solar cells - Electrical losses V oc, R sh, J 02 - Interface morphology between contact and Si wafer Conclusion Outline 6 th Metallization Workshop, Konstanz, Germany, /16

3 Problems in metallization with paste Screen-printing with conductive paste -simple process and cheaper cost Metallization with paste glass Ag Ag glass frit emitter c-si recombination shunting Significant effect Loss in V oc Severe limit of cell efficiency! 6 th Metallization Workshop, Konstanz, Germany, /16

4 Problems in Ag/Al metallization Ag/Al paste : Al addition Good contact to p + -emitter p + -emitter Ag/Al paste glass Ag n-si large spike - Shunting? - Recombination?? Al Complex composition glass Al? It s still a big question how glass frit and aluminum affect? The purpose of our study To elucidate the specific effects of Al 6 th Metallization Workshop, Konstanz, Germany, /16

5 Conventional evaluation for pastes Changing paste composition glass Ag Al - Ag - Glass frit - Aluminum Cell parameters = Complex system Indirect method to evaluate respective effects of materials in paste The conventional method cannot divide effects of glass frit and Al on cell parameters, accurately. How can we elucidate specific effects of Al? 6 th Metallization Workshop, Konstanz, Germany, /16

6 Floating contact method Standard H-pattern grid-contact detected emitter Floating contacts electrically and geometrically isolated from grid-contact Floating contact fraction 0% 5% 11% 16% busbar - Shunting - Carrier recombination effects on an emitter Advantages - Conductive - Nonconductive - Non-contact Al less Ag past to p + -emitter 6 th Metallization Workshop, Konstanz, Germany, 2016 R. Hoenig, Ph. D. dissertation, /16

7 SiN x /SiO 2 H-pattern grid contact: Ag/Al paste Test pastes - To elucidate specific effects of aluminum on p + -emitter Floating contacts: Three test pastes Only-Ag Ag Boron doped p + emitter 70Ω/sq. 156mmx156mm n-type c-si Phosphorus doped n + BSF 40Ω/sq. Effect of glass frit Ag/glass Effect of Al glass Ag Standard Ag paste Ag/glass/Al glass Ag Al Glass frit: PbO-SiO 2 -B 2 O 3 -ZnO 6 th Metallization Workshop, Konstanz, Germany, /16

8 Current density (ma/cm 2 ) Cell properties without floating contact No floating contacts Voc (V) Jsc (ma/cm 2 ) FF (%) Voltage 6 th Metallization Workshop, Konstanz, Germany, /16 Eff. (%) The cell parameters are good enough to evaluate the effects of floating contacts.

9 Open circuit voltage V oc (V) Open circuit voltage, V oc Same tendency Floating contact fraction (%) Conductive paste causes loss in V oc in n-type solar cells even if the paste does not contain aluminum 6 th Metallization Workshop, Konstanz, Germany, /16

10 Interface morphology underneath contact SiN x /SiO 2 contact p-si mirror HNO 3 /HCl HF HNO 3 /HCl Imprints of Ag/Al spike Imprints of Ag-crystallites fewer shallower Shunting?, Recombination? Shunting? Al mitigates generation of Ag-crystallites and their growth Adding Al causes forming the large spike 1µm 6 th Metallization Workshop, Konstanz, Germany, /16

11 Dark IV curves 10 2 Current density (ma/cm 2 ) hump Fraction:16% Voltage (V) Al mitigates the current increase at low voltage range. Numerical fitting with the two-diode model R sh, J 02 6 th Metallization Workshop, Konstanz, Germany, /16

12 Shunt resistance, R sh Shunt resistance R sh (Ωcm 2 ) mitigated Floating contact fraction (%) Al in Ag/Al paste does not induce significant shunting 6 th Metallization Workshop, Konstanz, Germany, /16

13 Recombination current, J 02 Recombination current density J 02 (10-9 A/cm 2 ) mitigated Floating contact fraction (%) Al mitigates the increase of recombination current 6 th Metallization Workshop, Konstanz, Germany, /16

14 Al effects on p + -emitter glass Al R sh, J 02 degraded R sh, J 02 mitigated Ag-crystallite fewer shallower 2.0µm The Al effects on Ag-crystallite mitigates the decrease of R sh and the increase of J 02 The large spikes do not induce the significant electrical losses 6 th Metallization Workshop, Konstanz, Germany, /16

15 Conclusion Specific effects of Al on p + -emitter can be elucidated by using the floating contact method with the homemade test pastes. Conductive paste causes loss in V oc in n-type solar cells even if the paste does not contain Al Al in Ag/Al paste mitigates shunting of pn junction and carrier recombination on p + -emitter by mitigating generation of Ag-crystallite and their growth The big metallic spikes underneath Ag/Al paste do not induce significant shunting of pn junction and carrier recombination The floating contact method have big advantages for elucidating respective effects of paste component on cell parameters. 6 th Metallization Workshop, Konstanz, Germany, /16

16 Thank you for your attention! Effect of Glass Frit in Metallization Paste on the Electrical Losses in Bifacial N-type Crystalline Silicon Solar Cells Takayuki Aoyama, Mari Aoki, Isao Sumita, Yasushi Yoshino, Yoshio Ohshita, Atsushi Ogura A Study on the Evaluation Method of Glass Frit Paste for Crystalline Silicon Solar Cells Mari Aoki, Takayuki Aoyama, Isao Sumita, Yasushi Yoshino, Atsushi Ogura, Yoshio Ohshita 6 th Metallization Workshop, Konstanz, Germany, 2016