Three potential manufacturing concepts have been identified for the Nano-Tandem cell, each with its specific advantages and challenges:

 

  1. Direct growth of III–V nanowire array on (100) silicon.
  2. Growth of nanowires on InP or GaAs, embedding in polymer and transfer to silicon.
  3. Aerotaxy of nanowires, array formation, embedding in polymer and transfer to silicon.

Direct growth of III–V nanowire array on (100) silicon

 

Directly grown nanowires. Reprinted with permission from M.Borg et al.: Vertical III–V Nanowire Device Integration on Si(100). Nano Lett., 2014, 14 (4), pp 1914–1920. Copyright 2014 American Chemical Society
Directly gronw nanowires. Reprinted with permission from M.Borg et al.: Vertical III–V Nanowire Device Integration on Si(100). Nano Lett., 2014, 14 (4), pp 1914–1920. Copyright 2014 American Chemical Society

Advantages

  • Monolithic approach
  • No III–V substrate needed
  • Direct epitaxial contact between Si and the III–V nanowires
  • Tunnel diode in nanowire has been demonstrated

 Challenges

  • Large area patterning of growth template
  • Reliable growth >200 nm of nanowires on Si solar cells
  • Epitaxy growth cost

 

Growth of nanowires on InP or GaAs, embedding in polymer and transfer to silicon

Transfer of nanowires
Transfer of nanowires

Advantages

  • High quality nanowire solar cells have been demonstrated on InP
  • Large growth parameter window
  • Nanowire arrays embedded and peeled off from substrate by use of polymer has been demonstrated 

Challenges

  • Large area pattern of metal seed particles
  • InP or GaAs substrate re-use necessary for low cost
  • Transfer and transparent electrical contact between nanowire array and Si cell (current matching)
  • Transfer and transparent insulating layer between nanowire array and Si cell (non-current-matched)
  • Epitaxy growth cost

 

 Aerotaxy of nanowires, array formation, embedding in polymer and transfer to silicon

 

Advantages

  • No III–V substrate needed
  • Fast, low cost gas-phase growth of nanowires demonstrated
  • Nanowire arrays embedded and peeled off from substrate by use of polymer has been demonstrated

Challenges

  • Alignment and embedding of Aerotaxy nanowires
  • Transfer and transparent electrical contact between nanowire array and Si cell (current matching)
  • Transfer and transparent insulating layer between nanowire array and Si cell (non-current-matched)

Next generation photovoltaics was among the topics in the Summer School on “Nanoscale Energy Converters”. The Summer School was held from 15-19 August 2016 in Falsterbo, Sweden.

The school featured outstanding international and local lecturers.

Some impressions from the Summer School can be found here.