Metrology for III-V materials based high efficiency multi-junction solar cells

Silicon solar photovoltaic (PV) generation capacity has grown rapidly, supported by subsidies that boosted take-up, and cost reductions from competition and manufacturing economies of scale. Another cost reduction strategy is to improve PV module efficiency, that has the added promise of compactness. Multi-junction solar cells (MJSC) are a promising technology, made of several layers of various semiconductors designed to absorb greater proportions of sunlight frequencies than silicon alone. MJSCs already offer much higher efficiencies than silicon PV cells. In time, advances in manufacturing processes and materials may result in even higher efficiencies, perhaps enabling PV to compete directly on cost with more conventional energy sources. However, development breakthroughs will require more reliable methods to measure important parameters, including light conversion efficiency.

This project developed a range of measurement techniques that support the development of more efficient MJSC solar cells.

The project:

• Developed traceable, reliable, cost-effective calibration methods, and measurement standards, to measure MJSC device efficiency and other parameters to equivalent levels of confidence as for silicon.
• Produced Good Practice Guides for MJSC calibration procedures.
• Designed, fabricated and characterised new types of connectors between cells.
• Developed modelling methods to understand the movement of electrons across these connectors, capable of providing insights for other areas of electronics and photonics.
• Developed methods to accurately measure electrical properties of MJSCs at the nanoscale, and developed a gallium arsenide reference sample.

Delivering impact
During the project, the Spanish space agency Instituto Nacional de Técnica Aeroespacial helped the Finnish solar simulator manufacturer Endeas Oy solve measurement issues for its single and multi-source solar simulators used to calibrate component cells and triple junction MJSCs.

Project outputs contributed to the standard IEC 60904-8-1 Measurement of spectral responsivity of multijunction photovoltaic devices, published in May 2017. Applicability for testing to this standard was promoted by a UK-based SME instrument manufacturer in publicity for a photovoltaic characterisation system. This company stated that IEC 60904-8-1 provides important new information on specific test requirements for multi-junction PV devices.

The project established the measurement infrastructure needed to accelerate the development and adoption of more efficient multi-junction solar cells, that could lead to cell modules capable of generating electricity at a cost-competitive basis.

EMPIR project 20IND12 Elena builds on this work.