Status and Future of Perovskite, Organic, and Hybrid Photovoltaics

With climate policies a continuing concern, there is inevitably discussion on energy transition towards sustainable renewable sources.

Solar cells are unquestionably part of the answer. As shown below, photovoltaic technology has come far in terms of reducing $/W and expanding global production capacity. In fact, solar cells are now financially viable without subsidy in many regions of the world. The installations are also rapidly growing every year as solar cells become a major part of the global energy mix.

The solar technology of choice today is of course wafer based silicon. As shown below, this technology is long established as the winning technology, limiting the space for other solutions including thin film solar cells. Given this dominance, an important question is whether Si will forever retain its current pole position? or will other technology options rise to complement and/or displace silicon?

In most technology fields many technology transitions take place. These transitions brew in the background for decades, often with dim prospects, but they eventually come of age to displace the old guard. There is no fundamental reason to assume solar technology will be any different, especially as silicon as is appears to have matured, reaching limits of its performance.

On the hand, silicon has proven extremely resilient in the electronic field. It never ceases to surprise and progress. However, even in this field, many non-silicon semiconductors now occupy mighty roles in, for example, high frequency or high power electronics. Furthermore, despite the unimaginable cumulative human hours of development time and capital thus far dedicated to silicon electronics, it remains an open question whether silicon alone can sustain the future roadmap, leaving an open space for alternatives such as 2D materials.

In this article, we provide you with detailed background information, outlining the status and trends of these solar technologies for outdoor and indoor applications. This will help set the importance of the themes of this conference in context. Here we discus organic PV, perovskite PV, and techniques such as R2R processing, inkjet printing, etc.

Source: data from charts by Fraunhofer ISE, adapted by TechBlick. Left: annual global production. Left: share of thin film PV technologies. The rest of the market share goes to Si. Become an Annual Pass holder to watch this content on-demand

Perovskites: the winning technology of the future?

There has been talk of the third generation of photovoltaics for decades. Two main classes of solar cell technologies studied were organics and dye sensitized solar cells (DSSC), which later evolved in the fastest improving PV technology: perovskite photovoltaics.

The chart below shows the improvement trajectory of several non-silicon photovoltaic technologies at the champion cell level. All the red lines refer to perovskite PVs, either as standalone or in tandem form.

Since appearing on the block around 2014, they have shown an incredibly fast EQE improvement trend. Interesting, this trend still has some room to continue, especially for tandem versions (perovskite/CIGS or perovskite/Si). The steep curve shown below has made perovskites the darling of the industry as well as investors worldwide. For some years, it also stole the limelight from OPVs.

Source: TechBlick. Adapted from NREL data. Become an Annual Pass holder to watch this content on-demand

Despite the fast cell-level improvements, technology barriers to full-scale commercialization still remain. One challenge is that the transition away from small champion cells to larger cells and modules is accompanied by a steep loss in efficiency. This is shown below. This data is from 2020/2021 and there are constant improvements. Nonetheless, this area still needs to be addressed. At this conference, you will hear from the likes of CubicPV who are reporting record stability results and plan on investing more than $1Bn in scale-up.

Another challenge has been the high rate of degradation of perovskite solar cells, limiting their useful lifetime. There is an improvement though at both the cell and module levels, as shown below on the right. Here, you can see the degradation rate of PCE of cell- and module-level perovskite PVs compared to well-established technologies such as crystalline Si, polycrystalline Si, CdTe, a-Si, and CIGS. Interestingly, the gap with acceptable commercial degradation level is generally shrinking, and there are also specific reports where this gap is fully bridged.

Another challenge is of course with the presence of lead in best performing perovskite PVs. This is an important issue but due to lack of space in the article, we will not address it further.

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Manufacturing perovskites, be they single or tandem cells, is an important question. Physical vapour deposition currently gives the best results. Most firms pursuing tandem cells use this technique as it yields more stable cells thank to better control of the thin film properties.

In perovskite-only cells, thin film deposition techniques may prove cost competitive against wafer-based silicon. This did not turn out to be the case with amorphous silicon. However, perovskites are far more efficient than a-Si and can thus halve the $/W cost even with the same equipment costs and production parameters.

In tandem perovskite cells, thin film processes offer an immediate approach for compatibility with existing silicon lines, enabling one to leverage perovskite solar cells to increase the efficiency of the well-established silicon cells. Without this booster technology, silicon may have reached the limits of its performance, exposing it to risk of technological disruption. Therefore, perovskite thin film cells can be the saviour of silicon photovoltaics if proven stable and non-toxic enough.

To achieve scales beyond what wafer technology can reach, many are developing printing R2R-based approaches, borrowing from the learnings of the OPV development. Here, some are targeting 1.5m webs running at an incredible (for this sector) 30m/min web speeds for unwind-to-wind fully-R2R perovskite PVs. The cleaner interlayer interfaces, compared to the interweaving donor-acceptor morphology of OPVs, might make it simpler than OPVs provided good perovskite inks are developed.

Visit our extensive on-demand library to hear from leading researchers working on solution processing as well as R2R coating of perovskite photovoltaics as VTT and Swansea Universities. These will be overview talks, outlining the state-of-the-art and offering unbiased benchmarking.

At the same time, you will hear from companies trying to commercially R2R produce perovskite PVs or start-ups developing novel perovskite inks such as Solaire Enterprises. We also highlight R2R production of tandem quantum dot-perovskite solar cells by the likes of QDSolar, a novel early-stage approach that might combine the best of both emerging technologies.

Finally, perovskite solar cells can also be inkjet printed. This has the advantage of freedom of design as well as the ability to integrate materials. You will hear from Saule Technologies, scaling up inkjet printed solar cells (42k sqm per year) with a strong application pipeline, and from Brite Solar scaling up inkjet printed photovoltaics to larger area solar cells.

Left: EMC’s high speed R2R solar pilot line with flexographic printed metal mesh transparent conductive layer on 100um Corning glass. Right: Inkjet printed perovskite PVs by Saule Technology on glass and some indoor application examples. Become an Annual Pass holder to watch this content on-demand.

Organic photovoltaics: Renaissance?

As shown in the efficiency vs year chart, organic photovoltaics have had a development history of 20 years already. The technology had a setback after the bankruptcy of Konarka, stalling commercial and technological development. This is reflected in the slow incremental growth of OPV efficiency between 2011 and 2018. However there have been jumps in efficiency since then with OPV cells exceeding 18% certified efficiency.

The material developments, and the mastery of the art of nanoscale donor-acceptor morphology control, will further sustain this development trend. In particular, in recent years, the transition to non-fullerene acceptors has rejuvenated the development trend, leading to ever higher efficiency level.

All manners of material developments now continue apace, shaping the future of OPV technology. At the TechBlick live(online) conference on 1-2 December you will hear from the likes of Brilliant Matters, Phillips 66, Solaire, and others discussing development of organic and perovskite materials.

Source TechBlick. Adapted from Swansea University data. Become an Annual Pass holder to watch this content on-demand

In parallel, and equally important, there is now significant accumulated production level technical learnings in the industry. At first, Konarka raised enormous sums of money but the bubble of hype around OPV technology burst with its bankruptcy.

Konarka suffered from bad timing at that time. China massively expanded Si cell production capacity through financing and other state-support backings, changing the competitive landscape with the plummeting $/W prices. However, Konarka also made technology errors. It wanted to scale up too soon and tried to scale up using an existing non-custom ex Polaroid 1.5m-wide web machine which could not be optimized to boost the efficiency of the OPV cells. As such, despite the investment, it never managed to approach the 5% efficiency level and never ran the machine close to its intended web speed levels. The industry has learnt these lessons.

In fact, despite this set back, the industry continued its developments. There was some degree of technology consolidation through mergers and acquisitions, and more importantly excellent built up of technical expertise.

As shown below as an example, companies can now process on wider webs with good uniformity. This specific example is from Sunew in Brazil. They print on 0.5m webs with lengths upto 1.5Km. They have five print stations and 32 printing lines (with double sided it becomes 64).

As shown below, they can maintain a thickness uniformity across the web of <2%. Furthermore, they achieve a relatively constant EQE as the web is scaled. This is no easy feat to achieve. Furthermore, they reduced the number of dummy runs to reach consistency between runs to <<3. You can also see various installation examples, showing that this technology is still not ready for utility-level energy production, but is finding niche unique uses elsewhere.

Sunew is not alone in scaling up R2R production of organic OPVs. Armor (ASCA) is also scaling up solution processed bulk heterojunction OPVs. Heliatek is mastering the complex art of R2R evaporation of tandem OPVs.

At TechBlick's LIVE (online) conference which took place on 1-2 December 2021 you could hear from all the key players in this field including Sunew, Armor, and Heliatek live. You can also meet the speakers from these firms in the interactive 'in person virtual' rooms to mingle and discuss further. You will also hear from equipment manufacturers such as Coatema whose expertise and custom coating machines play a pivotal role in the development of this industry.

Data from Sunew. Adapted by TechBlick. Become an Annual Pass holder to watch this content on-demand

Not everyone is also focused on outdoor or BIPV applications. This makes sense as OPV efficiency and costs are not yet close to being good enough for competing directly with Si or CdTe technologies.

In contrast, a strong selling point and a differentiating factor for OPVs has always been their ability to outperform standard Si cells under low-light indoor conditions. In some cases, as NRCC will show at our conference, the efficiency indoors can approach 30%.

This explains the strong focus on indoor energy harvesting applications of OPVs, especially seeking to offer a fully integrated module to replace coin cell batteries or extend their lifetime such that they become fit and forget solutions.

One barrier against the adoption of OPV energy harvesting is the high cost of energy production by OPVs. To overcome this, R2R techniques may become useful.

As you will learn, these companies are going further than ever before and almost all of them are directly benefiting from the technology developments of previous generation of players in the field. Some have taken over equipment at lower costs which was originally intended for other applications, whilst others have absorbed the intellectual property as well as technical know-how of previous players. Therefore, one can easily recognize a long running thread within, and a shared heritage across, all these developments.

Customization of design or free-form design has been another differentiating feature of organic solar cells. Here, inkjet printing can become very design, enabling one to rapidly try out different designs as well as different active materials and green solvents. At the TechBlick conference on 1-2 Dec 2021, you will hear from Dracula Technologies, one of the pioneers in this field. Dracula has plans to push capacity to 5000k pcs by mid 2023, thus showing that inkjet printing can also be a good choice for industrialization of OPVs targeted at indoor applications. Finally, when it comes to photovoltaics (organics, CIGS, QDs), passivation is a key component. Often higher permeability levels are required (>10E-4g/day/sqm), mandating multi-layer structures consisting of pairs of organic-inorganic layers. This, and currently low production volumes, add to costs of barrier films. These films in turn are a major cost component, driving up the price of OPVs and other solar cells. It is a classic chicken-and-egg problem for this industry.

Despite this, good technical solutions are now available, and maturing. The prices have also been falling fast, even if not fast enough. In addition to barrier properties, additional features like UV protections are also introduced. At this conference, you can hear the latest from two leading players, 3M and ITRI. The former is a major player in the field and the latter has a very novel unique solution.

Join TechBlick as an Annual Pass holders to get access to all on-demand content from our past conferences and listen presentations from the key players working in OPV developments such as Sunew, Armor, Heliatek, Epishine, Dracula Technologies, Brilliant Matters, Phillips 66, Coatema, InfinityPV, and others. Also hear from interesting approaches towards R2R processing of CIGS. FlisomAG with technology from Empa is very advanced in terms of R2R production with off-the-shelf ready-to-sell product portfolio of high-performance flexible CIGS.

One final point is that printing or R2R processing are not unique to organics or perovskites. CIGS can also be R2R produced. Those with a history in the industry might remember some well-funded companies seeking to R2R print CIGS inks.

Source: Inkjet printed OPVs from Dracula.

Become an Annual Pass holder to watch on-demand presentations from our conference "The Future of Photovoltaics. Organic, Perovskites, CIGS, Hybrid" which took place on 1-2 December 2021:

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