Crystalline silicon solar cells dominate the global photovoltaic market with module efficiencies of around 20-22%. However, the field of solar energy wants innovative materials and approaches that yield even higher efficiencies in support of global renewable energy goals. Tandem solar cells combining silicon and perovskite sub-cells are widely regarded as a very promising, high-performing and viable alternative to conventional crystalline solar cells, and King Abdullah University of Science and Technology (KAUST) is leading the charge in the field of research. Researchers in the KAUST Photovoltaics Laboratory (KPV-Lab) of the KAUST Solar Center have produced a perovskite/silicon tandem solar cell with a power conversion efficiency (PCE) of 33.2% — the highest tandem device efficiency in the world to date, surpassing that of Helmholtz- Zentrum Berlin's (HZB) record at 32.5% PCE. The European Solar Test Installation (ESTI) certified the tandem device and listed it at the top of the National Renewable Energy Laboratory's (NREL) Best Research-cell Efficiency Chart. Led by Dr Stefaan De Wolf, Professor of Material Science and Engineering and Interim Associate Director of the KAUST Solar Center, the team has steadily been perfecting the perovskite/silicon tandem cell concept since 2016 — developing new materials, methods and device structures, and tackling fundamental challenges, such as how to uniformly cover the micrometer-sized pyramidal surface of silicon cells with perovskite material. The resulting tandem solar cell combines perovskite top cells with industrially compatible, two-sided textured silicon bottom cells. The perovskite top layer absorbs blue light best, while the silicon foundation absorbs red light best. The combination of these materials maximizes the capture and conversion of sunlight into electricity more efficiently than the conventional single-junction silicon analogues. The innovation is a significant breakthrough in the field of solar energy at a time when market predictions estimate that tandem perovskite/silicon technologies will comprise more than $10 billion of the global photovoltaic market share by 2032. "This new record is the highest PCE of any two-junction solar cell under non-concentrated light, attesting the tremendous promise of perovskite/silicon tandems to deliver ultra-high performance photovoltaic modules, which is critical to rapidly achieve renewable energy goals towards combatting climate change," De Wolf said. The collective knowledge and skills of several lead researchers have contributed to the recent achievement, in particular, Dr Esma Ugur, who specializes in optical spectroscopy and the analysis and visualization of cell defects; Dr Erkan Aydin, an expert in the scalability and stability of ultra-efficient tandem solar cells; and Dr Thomas Allen, who focuses on c-Si bottom cell development. The team is currently exploring scalable methods to produce industrial-scale perovskite/silicon tandem cells with areas exceeding 240 square centimeters, as well as strategies to obtain highly stable tandem devices that will pass the critical industrial stability protocols.
