Thinned Germanium Substrates for III-V Multijunction Solar Cells

TL;DR

This paper investigates the effects of thinning germanium substrates on multijunction solar cells, demonstrating that reducing substrate thickness to 115μm can improve performance and manufacturing feasibility.

Contribution

It introduces a substrate thinning approach for Ge-based multijunction solar cells and validates its effectiveness through simulation and experimental fabrication.

Findings

Thinning Ge substrates to 115μm is feasible.

Back surface recombination is critical for performance.

Limited degradation observed in thinned solar cells.

Abstract

Multijunction solar cells are usually grown on Ge substrates. This implies several disadvantages that hinder the performance of the whole multijunction and limit their possible applications. The drawbacks caused by the substrate are: heavier devices, higher operation temperatures, lower performance and lack of photon confinement. In this work we propose thinning the substrate as a valid solution to the aforementioned challenges. The influence of the substrate thickness on the Ge subcell performance inside a multijunction is simulated using 2D TCAD tools. Simulation results point to the back surface recombination as the key parameter to enhance the development of thinned Ge subcells. Ge substrates have been thinned down, achieving 115{\mu}m thick samples. Finally, solar cells have been manufactured out of the thinned substrates proving a limited degradation and showing the feasibility of this process to manufacture Ge subcells thinned down up to 115{\mu}m.