Wednesday morning’s Plenary Lecture in Area 3 was given by Dr. Ryan France from NREL who presented recent record efficiencies in III-V MJSCs incorporating inverted metamorphic strain- balanced GaInAs/GaAsP QWs. The innovations required to produce such high performance was to optimize the quality and number of QW layers by careful control of the strain surface in the QW sub-cell. The final structure included as many as 300 balanced and defect free QWs with both high voltage (low recombination losses) and high current. Additional improvements included optimization of the GaInP top cell via implementation of a post-growth annealing processes in a structure protected by a tunnel junction, and better control of the defect density and propagation in the metamorphic layer.
The Area 6 Plenary was given by Professor Jinsong Huang from UNC Chapel Hill who discussed the origin and role of point defects in metal halide perovskites. Dr Huang showed recent perovskite research based on Drive Level Capacitance Profiling (DLCP) to determine trap distributions in perovskite solar cells. It was shown that interface traps dominate the defect distribution and performance of perovskite solar cells. The origin of defects was discussed with both negative and positive traps observed in these materials and the chemical nature of the defects discussed. Iodine interstitials were shown to produce negative defect complexes, while MAI rich regions were shown to result in positive charge defects. While triple cation systems are known to be more stable, they still show significant defects but of a new type. Hole traps (iodine interstitials) at the PTAA interface were shown to dominate device degradation and losses though it was suggested these can be inhibited by excess AX3 incorporation (FAI3, MAI3).
The Area 11 plenary was given by Professor Annick Anctil from Michigan State University who discussed Anticipatory Sustainability Assessments of PV Deployment. Environmental concerns include (for example) effects on drinking water, solar farm noise, and solar waste. Professor Anctil described how genuinely sustainable implementation involves the nexus between economic, environmental, and social aspects of PV implementation; how will PV work with the rest of the power system, how is it disposed of, and what are the impacts of replacing “old” technology. An example of sustainability was discussed with respect to silicon solar cells and the availability of silica, which is often shipped to high producing countries increasing the carbon footprint of these systems. Large scale manufacturing of PV is also a significant contributor to their carbon footprint and will be so at the levels of implementation envisaged unless the grid is significantly decarbonized. The sustainability of PV was discussed in terms of consideration of the materials used and how these are produced, disposed of, and over what period. High efficiency and longer lifetime systems are required. The effects of land use and upon agriculture were also suggested to be important considerations, which require more careful impact assessments.
Wednesday morning’s session in Area 1 on “Ultrathin Photovoltaics” started with a presentation from Uwe Rau from Forschungszentrum Julich who discussed the difference in the thermodynamic and electrical description of the diode equation, while Elisa Antolin from Universidad Politecnica de Madrid described the need to control surface states in MoS2 solar cells and in doing so presented encouraging performance of 3.8 % PCE under AM 1.5G. Eduardo Camarillo Abad from the University of Cambridge presented comprehensive work on light trapping using transparent quasi random structures describing the flexibility of such layers and
the potential to improve ultrathin GaAs solar cells to 20% PCE. Hoon Jeong Lee from Johns Hopkins University described a machine learning protocol developed to assess materials and device characteristics driven my large data sets from a simultaneous suite of experimental measurements.
Highlights in Wednesday morning’s Area 4 session on “Passivated, Carrier-Selective, and Heterojunction Contacts” included a presentation from Felix Komoll (Forschungszentrum Julich) who provided a new approach to describe the fundamental operation of silicon solar cells in terms of thermodynamics, and Anh Huy Tuan Le from UNSW who demonstrated a high resistivity wafer that does not impact solar cell performance but is very tolerant to high voltage operation. Further highlights also included a presentation from Yifeng Zhao from Delft who described a two- step hydrogenated a-Si layer that improves solar cells performance.
Wednesday’s Area 6 session on “High Efficiency Perovskite Solar Cells and Tandems” included several impressive high-performance results including a presentation from Antonio Agresti from the University of Rome Tor Vergata who described interface engineering using graphene and MXenes layers to increase the stability of 2T mechanically stacked tandems achieving PCE > 28.7%. Silvia Mariotti from H-Z Berlin reported the first experimental demonstration of a perovskite/POLO/PERC tandem cell with and initial PCE of 21.3 % on a p-type c-silicon bottom cell which increased to 27 % when implemented on a n-type c-Si bottom cell. Christian Wolff from EPFL presented a 29 % perovskite/silicon tandem realized via a fluorinated additive in the hybrid perovskite to improve the morphology and suppress recombination at the ETL interface.
In Wednesday afternoon’s Area 8 session on the “Effects and Mitigation of soiling on PV systems,” Luke Jones from Loughborough University compared fluorinated and non-fluorinated hydrophobic coatings in accelerated lifetime tests, which indicated that the loss of fluorine and hydrophobicity occurs after > 750 hours of UV exposure. Bennet Meyers from SLAC proposed a novel soiling extraction model based on signal decomposition, a machine learning technique. It was suggested that this method can be applied to any system and can also work if no irradiance data or metadata are available.
Wednesday lunchtime saw the Special Session: “Towards 100 % Renewable Energy” in which several speakers across Industry, National laboratories, and the Federal Agencies emphasized the size of the task of decarbonization and the challenges this presents. Highlights included Teresa Barnes from NREL who emphasized the need for reliable and long-life PV modules and that these systems should be implemented fast and moreover, that the community should work together and focus on removing fossil fuels not alternative PV systems. Vasilis Fthenakis from Columbia University suggested that there is a strong need to implement affordable PV with the lowest environmental impact and that despite reservations of others that there are sufficient materials and land resources for large scale PV implementation that can be improved further with innovations from the community. Nicole Steele from the Department of Energy described the proposed expansion of community solar and the need for more equity in solar, which is a major objective of the current US administration.