Technological guidelines for the design of tandem III-V nanowire on Si solar cells from opto-electrical simulations

- Comprehensive design rules for tandem III-V nanowire on Silicon cell are reported.
- Guidelines for selecting optimal cell geometry and doping profiles are given.
- Critical doping for the core-shell junction is determined.
- Dominant part of surface recombination is localized at the bottom nanowire surface.
- ITO serves as an antireflection coating for dense nanowire arrays.

Effect of geometrical and structural parameters on the efficiency of the tandem solar cell based on the III-V nanowire array on silicon is studied by the means of coupled opto-electrical simulations. A close to realistic structure, consisting of AlGaAs core-shell nanowire array, connected through a tunnel diode to a Si subcell is modelled, revealing the impact of top contact layer, growth mask and tunnel junction. Optical simulation of the tandem structure under current matching condition determine optimal geometrical parameters of the nanowire array. They are then used in the extensive electrical optimization of the radial junction in the nanowire subcell. Device simulations show the necessity of high doping of the junction in order to avoid full shell depletion. The influence of bulk and surface recombination on the performance of the top subcell is studied, exposing the importance of the good surface passivation near the depleted region of the radial p−n junction. Finally, simulations of the fully optimized tandem structure show that a promising efficiency of η=27.6% with the short-circuit current of JSC=17.1mA/cm2 can be achieved with reasonable bulk and surface carrier lifetime.