Quantum-engineered lattice-matched III-V-on-Si multijunction solar cells

Introduction

Photovoltaics is called to be a main player in the global transformation of the energy sector the world is facing to fight climate change. Multijunction solar cells, based on classical III-V compound semiconductors, are the most advanced photovoltaic cells holding a record photoconversion efficiency of 38.8%.

Challenges of Current Technologies

However, the high cost associated with their manufacturing process has typically relegated this technology to non-terrestrial applications in favour of Si cells. On the contrary, single-junction Si cells are cost-effective, but there is almost no room left to further improve their efficiency, which already approaches its theoretical limit of 29.4%.

Objectives of MIRACLE

MIRACLE is created to make true a dream of decades: combining the unbeatable efficiency of multijunction solar cells with the cost-effectiveness of Si technology. The ultimate objective of MIRACLE is the demonstration of both double- and triple-junction solar cells based on III-V materials pseudomorphically grown on top of a Si cell, configurations that promise photoconversion efficiencies of up to 43% and 47%, respectively.

Use of Quaternary Dilute-Nitride Alloys

Quaternary dilute-nitride alloys are the only III-V compounds that can be grown lattice-matched to Si with ideal band gaps for the fabrication of multijunction solar cells in combination with a bottom Si cell.

Fabrication Challenges

Nevertheless, despite their well-known potential, reports on dilute-nitride solar cells are rather scarce yet due to their challenging fabrication with the high structural perfection demanded in photovoltaics.

Revolutionary Approach

The revolutionary idea of MIRACLE is to make use of quantum engineering to fabricate dilute-nitride compounds lattice matched to Si not as thick layers, as attempted so far, but as short-period superlattices by periodically alternating simpler compounds on an atomic-layer scale.

Conclusion

Hence, MIRACLE does not only aim to push the efficiency of cost-effective Si-based tandem solar cells to their theoretical limits, but also to unveil the physical properties of unexplored quantum heterostructures.