37th EU PVSEC, 07 - 11 September 2020

16 July 2019

Let us introduce you to Topic 3 “Perovskites, other Non-Silicon-Based Photovoltaics and Multi-Junction Devices” today

Topic 3 addresses the wide range of technologies beyond crystalline Silicon. Even though the current market share of these technologies only accounts for about 5%, it is not only a driver of low-cost production but also a very active and successful research field. It is continuing due to the surprising progress in efficiency of Perovskites solar cells, which achieved on a laboratory scale already around 20% after only a couple of years. With 21 oral presentations the Perovskites take the lead in the coverage of Topic 3 at EU PVSEC2019, closely followed by CIGS technologies.

The majority of presentations on Perovskites deal with heterostructures like Perovskite-Silicon Tandems. The plenary presentation “Towards Highly Efficient Monolithic Tandem Devices with Perovskite Top Cells” [3CP.1.2] gives guidance on how to boost Perovskite tandem efficiency to values above 30%, by integrating perovskite top-cells monolithically on top of CIGS bottom cells. The authors will show in this presentation how they succeeded to reduce the current mismatch when the device is exposed to the standard AM 1.5 solar spectrum.

In contrast to the previously described results which were achieved using devices with active areas of less than 1 cm2, the results with larger devices are described in the presentation “Processing of Large Area Perovskite-Based Solar Devices: High Efficiency and Stability Assessment” [3CO.6.4]. Amongst other data, this work illustrates results on mini-modules consisting of 8 Perovskite cells with average efficiencies of up to 15.9% for a module active area of 10 cm2.

The title “Perovskite Silicon Photovoltaics: The Joule in the Crown of Low-Cost Electricity” [3CO.8.4] promises an interesting overview about the opportunity for perovskites to increase the efficiency of low-cost Silicon solar cells beyond the single-junction limits. The presentation will discuss the specific challenges to push solar cell efficiency beyond 30% and the already achieved record performance of perovskite silicon tandem solar cells with an efficiency of at least 28 percent. Furthermore, it will explain fundamental loss mechanisms in the perovskite absorber and contact heterojunctions as well as the aspects of optical design and deployment in mono- or bifacial format. The author who is responsible to transfer this technology to a commercial pilot-scale will also report promising reliability data indicating that the cells meet or exceed the cell tests embodied in the IEC61215 protocols.

Whilst on the subtopic of organic and dye-sensitised solar cells’ continuous improvements will be reported at EU PVSEC, you should not miss the presentation “Power Performance and Thermal Operation of Organic Photovoltaic Modules in Real Operating Conditions” [3CO.7.3]. The authors measured and analysed very thoroughly the real-world performance of printed organic cells. In particular the thermal behaviour of the module has been studied in order to show how the performances of organic PV devices are affected by the temperatures they can reach under natural sunlight. Interestingly and in contrast to all other solar cells, there seems to be an optimum operating temperature depending on the irradiance as power decreases both below and above this temperature. The results should allow substantiated forecasting of long-term energy output of such devices and open a level playing field for the commercialisation of this technology.

From the many presentations on CIGS technology one should not miss the invited keynote plenary titled: “Research and Innovation in CIGS and its Alloys - Which are the Next Bottlenecks?” [3CP.1.1]. We expect to hear the most relevant results of the EU-funded ARCGIS-M project, which aims to reduce the use of Indium and Gallium by enabling the use of ultrathin CIGS layers. Whilst it seems that the material-scarceness of Indium and Gallium can be resolved, it will now talk about bottlenecks on the passivation, the substrate (stainless steel foil) and its optical reflection property. The project involves 15 partners from six European countries.

There is a Student-award Finalists presentation which also addresses the challenges of making CIGS cells thinner: “Submicron CIGS Solar Cells: Feasibly towards the Absorption Limit” [3AO.8.2] describes a comprehensive modelling framework for the light-management of the back reflector of such cells. The author proposes to incorporate interdigitated back contacts and claims to improve the optical performance by 38%. Such structure could even be applied to Perovskite/CIGS tandem cells!

In the presentation “Characterization of High Bandgap CIGS Solar Cells and Corresponding Absorber/Buffer Interfaces: Results of the EFFCIS Project” [3AO.9.4] you will be briefed about a significant German project with 14 partners (one of which is from the US) which wants to gain better physical understanding of high band-gap CIGS cells well as their structural features following post-deposition treatment.

Topic 3 also includes the presentation on III-V cells, also known as the “Efficiency Formula One” in photovoltaics. The plenary “Recent Progress of Solar Cell Development for CPV Applications at AZUR SPACE” [3CP.1.3] will give an overview about the technology status of such cells. It will demonstrate the continued demand on very high efficiency devices and looks into the prospects to manufacture now 4-junction or even 5-junction devices. These developments aim to achieve 46% efficiency at high concentration. Adding to the already complex Ge/xxGaAs/xxGaP compounds another fifth active InGaP layer increases significantly voltage and reduces current-induced losses. This is the plenary which explains the technology behind the top-runners of all efficiency charts!

If you want to be informed about another approach to high efficiency in triple-junction device, the presentation “Bragg Reflector within Triple-Junction Solar Cells for Spectrum Splitting Applications” [3BO.8.1] is the place to go. The authors use spectrum splitters, where Bragg reflectors together with a dichroic mirror are used to filter for each of the four spectrally optimised cells the right spectral band out of concentrated sunlight. This concept, which looks at 44.4% efficiency seems to be a choice for direct electricity generation at large central receiver power plants which so far used sunlight only for thermodynamic conversion.

Finally, an application for space flight will be presented in “Photovoltaic Operation in the Low Atmosphere and at the Surface of Venus” [3BO.8.6] which would not be possible with any other technology than double-junction GaInP/GaAs. The operating environment on the planet Venus is in fact very demanding: 465 °C would destroy any conventional semiconductor almost immediately, but for the II-V cells it looks like at least 3 weeks lifetime! Moreover, ground-level irradiance is only 10% of that on earth, so highest efficiency is a must. The presentation will also display how to optimise the chosen solar cell technology to the varying solar spectrum received during the descent through Venus’ atmosphere. For measurements of lifetime some prototype cells have been heated to the expected surface temperature of Venus which is as high (450 °C) as the hot plates of an electric cooking oven! We hope that the cells will also survive the Sulfuric acid contained in the atmosphere. You might think that such research is of limited use to solve our planet’s energy problem, but much of our scientific knowledge including on atmospheric phenomena is based on spacecrafts powered by photovoltaics… and the atmosphere of Venus which contains 96% of CO2 is one of the extremes created by a “runaway” greenhouse effect… Even though it cannot happen on earth in the near future, we hope to learn from these space missions how to treat our planet in the right way...