Challenges facing copper‐plated metallisation for silicon photovoltaics: Insights from integrated circuit technology development

Abstract

Copper‐plated interconnects were widely adopted for volume manufacture of integrated circuits after more than a decade of intensive research to demonstrate that use of Cu would not impact device reliability. However, although Cu‐plated metallisation promises significantly reduced costs for Si photovoltaics, its adoption in manufacturing has not gained the same traction. This review identifies some key challenges facing the introduction of Cu‐plated metallisation for Si photovoltaics. These include the following: (1) increased carrier recombination due to the use of Cu for metal contact formation; (2) reduced module reliability due to adhesion or contact integrity failures; and (3) limited availability of cost‐effective processes and equipment for metal plating. For integrated circuits, Cu's low electrical resistance and high resistance to electromigration provided an impetus for the large investment in process development that was required to realise Cu‐plated interconnects. However, the technical advantages of using Cu for Si solar cell contacts are not as compelling, as solar cells can tolerate larger feature sizes thus reducing the criticality of the contact metal's conductivity and electromigration properties. Additionally, for Si photovoltaics, low cost is paramount, and new challenges arise from the need for modules to absorb light and operate in the field for 25+ years in diverse outdoor climates. However, with the scale of Si photovoltaic manufacturing expected to increase dramatically in the next decade, the use of large quantities of silver for cell metallisation will provide an incentive to address reliability concerns regarding the use of Cu for Si photovoltaic metallisation.

Degradation of copper‐plated silicon solar cells with damp heat stress

“…However, as the global PV industry matures and grows, there continues to be a need to pursue new materials and processes that may reduce manufacturing costs and/or improve performance. Screenprinted Ag is the second largest material cost component in typical crystalline silicon (c‐Si) solar cell manufacturing processes, behind only the light‐absorbing c‐Si wafer 1 . Reducing or eliminating costly and scarce Ag from PV has both near‐term financial and long‐term sustainability advantages.…”

“…A long‐proposed alternative is electroplated copper (Cu). The price of Cu is 1%–2% the price of Ag by weight, plated Cu is a better electrical conductor than screenprinted Ag paste, and plated Cu has a history of successful use as a conductor in integrated circuits 1 . Despite these advantages, industry projections at increased market share for Cu‐plated contacts have not materialized, and successive projections tend to be revised downward and pushed back in time 2…”

Selective seed layer patterning of PVD metal stacks by electrochemical screen printing for solar cell applications

“…After the successful structuring of Al/Cu stack using ESP, a further metal layer in the Al/Cu stack will be necessary in the next step. This layer would act as a diffusion barrier to guarantee the long‐term functionality of IBC solar cells …”

Effect of co-sensitization of InSb quantum dots on enhancing the photoconversion efficiency of CdS based quantum dot sensitized solar cells

“…Dye sensitized solar cells (DSSCs) (Gratzel cells) and quantum dot sensitized solar cells (QDSSCs) are promising solar cell technologies as they utilize dye and quantum dots (QDs) as light sensitizing materials. [1][2][3][4][5][6][7] DSSCs have several limitations such as poor stability of the dye molecules, high cost of dyes, and single wavelength absorption which restricts their applications, 8 whereas QDs exhibit excellent properties like tunable bandgap, multiple carrier generation and high absorption coefficient. Therefore, QDs based sensitized solar cells are more promising compared to DSSCs.…”