METACELLS · Advanced epitaxy of metamorphic semiconductor structures for multijunction solar cells
FP7 — People (Marie Curie Actions)
- Duration
- 2013-03-01 → 2016-02-29
- EU contribution
- €256,206
- Participants
- 1
- Scheme
- MC-IOF
Lines connect the coordinator with its partners.
Results in brief
Advanced epitaxy of metamorphic semiconductor structures for multijunction solar cells
The global objective of METACELLS project is “to develop the epitaxial technique for the growth of metamorphic semiconductor structures that allow realizing the full efficiency potential of multijunction solar cells, paying special attention to the subsequent manufacturability and cost effectiveness of the solar cells developed”. During the first period (outgoing phase) of METACELLS project, the work towards this objective has led to outstanding results, which have advanced the technique and have enabled the attainment of world record efficiencies of photovoltaic conversion with quadruple-junction solar cells. Lattice-mismatched subcells for 3-junction and 4-junction solar cells have been developed. The focus was put on developing the epitaxy process for the 1eV Ga0.76In0.24As metamorphic junction, which has a large lattice mismatch of ~2% with respect to the GaAs substrate. In summary, high quality ordered GaInP-based CGBs for Ga0.75In0.25As grown on GaAs substrates have been achieved, with threading dislocation densities < 5·105 cm-2. This has enabled the implementation of high quality 1eV Ga0.76In0.24As metamorphic subcells with carrier collection efficiencies nearing 100%, internal luminescence efficiencies of ~ 90% and Eg/q-Voc < 0.35 V (see Figure 1). This result debunks the traditional belief that metamorphic semiconductor structures have necessarily poorer electronic characteristics than latticematched structures, and opens the way to further developments of metamorphic structures for solar cells or any other semiconductor device. Both triple and quadruplejunction metamorphic solar cells structures have been implemented successfully by tackling challenges such as the development of a high performance Ga0.76In0.24As/GaAs0.75Sb0.25 metamorphic tunnel junction and studying and minimizing the influence of the metamorphic growth on these complex solar cell structures. This work has enabled the implementation of both triple and quadruple-junction metamorphic solar cells structures, achieving world record efficiencies for photovoltaic conversion. The potential for future advancement in the performance of these devices has been analyzed, concluding that the metamorphic multijunction solar cell technology will allow surpassing the 50% photovoltaic conversion efficiency for concentrator terrestrial applications in the medium term. Moreover, metamorphic structures offer also the benefit of an easily tunable bandgap combination to maximize the energy output of concentrator or 1-sun systems at sites with different spectral variations due to different climatic conditions. All in all, this technology will contribute decisively towards the goal of achieving a cost-competitive clean energy source.
Data: CORDIS, © European Union
Project objective
The objective of METACELLS project is to develop the epitaxy technique for the growth of metamorphic semiconductor structures that allow to realize the full efficiency potential of concentrator multijunction solar cells, paying special attention to the subsequent manufacturability and cost-effectiveness of the solar cells developed.Eventually, this growth technique will allow to fabricate a monolithic multijunction (3 - 4 junctions) solar cell exhibiting ~75% of the maximum theoretical efficiency calculated for the standard direct terrestrial spectrum (i.e. approaching 50%) at 1000 suns, using only one growth step and minimizing costly post-processing.The implementation of the optimum subcells bandgap combination, using materials with the required photovoltaic quality will be pursued. The metamorphic MOVPE growth technique will be revisited by in-depth understanding of strain and relaxation dynamics during growth of lattice-mismatched layers, using in-situ monitoring, which will be the central research topic. Development and functional multijunction cell structures, including the tunnel junctions, optimized for operation at 1000 suns, is aimed.The epitaxy routines for the growth of the step-graded buffer layers will be cost-optimized so that the process time and gases consumption are reduced while keeping the material quality unaffected. A decrease around 10% is projected to be attained, resulting in a similar reduction in fabrication cost.The accomplishment of METACELLS project objectives will contribute to widen current European excellence in high efficiency concentrator cells development and industrialization, allowing the many companies involved in this business to lead the market with the best performing product. This will enable Europe’s involvement in further research for solar cell development and will pave the way for the attainment of a photovoltaic technology suitable for mass production of electricity at competitive cost.
Original text from CORDIS.
Participants
- UNIVERSIDAD POLITECNICA DE MADRID · MadridCoordinatorSpain
Links
Data: CORDIS, © European Union