The realization of very high efficiency, stable perovskite solar cells fabricated on a large scale at low cost, has the potential to further lower the cost of photovoltaics. This necessitates an understanding of the properties required of the perovskite material, including the carrier mobility. Perovskite cells also feature mobile ionic species, and the impact of these ions on cell performance – and in particular, to what extent and under what circumstances they may limit device performance – is not well understood. Here, we employ an advanced numerical model that allows for the presence of mobile ionic species to probe the relationship between carrier mobility, the presence of ionic species as well as different possible recombination mechanisms within the cell. We show that a high electron and hole conductivity throughout the device is key to avoiding transport losses. For devices operating significantly below their radiative limit, achieving a sufficiently high conductivity requires high carrier mobilities of at least 10cm2/V-s. It is shown that the presence of a single mobile ionic species can lead to effective doping of the perovskite bulk, which is detrimental to cell performance by lowering the conductivity of one type of carrier. The results also indicate that increasing cell VOC closer to its radiative limit is also beneficial for reducing transport losses and pushing cell performance closer to its theoretical limit.
With commercial silicon solar cells approaching both practical and theoretical efficiency limits, there is growing research effort to develop new low-cost technologies capable of reaching efficiencies of 30% and beyond. Silicon-based tandems that combine current industrial technology with emerging thin-film PV materials are considered the most cost-effective option for achieving this, with the latest edition of the International Technology Roadmap for Photovoltaics (ITRPV) predicting Si-based tandems to appear in mass production after 2019. The rapid rise of perovskite solar cell performance in the past few years has made perovskites the material of choice as a top cell for such tandems due to their high efficiency and simple, low-cost fabrication.
Optimization of tandems requires detailed knowledge and characterization of the optical and electrical properties of every layer, as well as practical constraints imposed by processing sequences and chemical incompatibilities. This presentation will review the latest progress in perovskite-silicon tandems, including our recent demonstration of a 26.4% 4-terminal tandem, and a 22.8% monolithic tandem based on a diffused-junction silicon homojunction cell. Key challenges and potential pathways for reaching efficiencies of 30% and beyond will be identified and discussed.
Sliver solar cells are thin, mono-crystalline silicon solar cells, fabricated using micro-machining techniques combined
with standard solar cell fabrication technology. Sliver solar modules can be efficient, low cost, bifacial, transparent,
flexible, shadow-tolerant, and lightweight. Sliver modules require only 5 to 10% of the pure silicon and less than 5% of
the wafer starts per MWp of factory output when compared with conventional photovoltaic modules. At ANU, we have
produced 20% efficient Sliver solar cells using a robust, optimised cell fabrication process described in this paper. We
have devised a rapid, reliable and simple method for extracting Sliver cells from a Sliver wafer, and methods for
assembling modularised Sliver cell sub-modules. The method for forming these Sliver sub-modules, along with a low-cost
method for rapidly forming reliable electrical interconnections, are presented. Using the sub-module approach, we
describe low-cost methods for assembling and encapsulating Sliver cells into a range of module designs.
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