Weekend Learn: Attending to the underside of TOPCon degradation

From pv journal 09/23

Technological innovation continues apace, in a photo voltaic trade that might add 400 GW of era capability in 2023. This yr could possibly be as pivotal as 2016, when passivated emitter rear ccontact (PERC) photo voltaic cells supplanted again floor area know-how. TOPCon photo voltaic cells are the entrance runner to grow to be the brand new mainstream photo voltaic method and are gaining on PERC market share. Nevertheless, heterojunction (HJT) and back-contact cells are additionally rising in recognition.

Wanting again

In 2016, after PERC had already made important inroads, researchers and check labs turned conscious of degradation points. They noticed that the know-how was notably prone to: light-induced degradation (LID) and light-weight and elevated-temperature induced degradation (LeTID).

As soon as the basis trigger was recognized, cell and module producers shortly adopted mitigation strategies of their manufacturing processes, making certain PERC cells shouldn’t undergo extreme LID and LeTID charges.

In mid-2023, researchers and testing and certification laboratory specialists started warning TOPCon modules could be extra delicate to sure degradation mechanisms. The query is whether or not the problems flagged are indicative of inherent issues of TOPCon know-how or are a results of the supplies or course of manufacturing parameters of those early modules not having been absolutely tailored to the precise wants of the know-how.

Degradation remark

The alarm was first raised by Paul M. Sommeling and his collaborators from Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek (TNO). The crew from the Dutch analysis physique performed damp warmth checks to check the moisture-induced degradation affect of various encapsulation supplies on efficiency in bifacial PV modules. It discovered that the front-side metallization of negatively doped, “n-type” TOPCon cells gave the impression to be extra liable to acid- or moisture-induced degradation than positively doped, “p-type” equivalents.

The newest annual “PV Module Index report,” printed in Might by the Renewable Power Take a look at Heart, a third-party testing lab, indicated that n-type TOPCon cells could have increased susceptibility to ultraviolet-induced degradation (UVID).

In June, Asier Ukar, director of testing physique PI Berlin Spain, voiced considerations that producers weren’t absolutely conscious of various degradation mechanisms when switching from PERC to TOPCon cell manufacturing.

pv journal has approached scientists and certification specialists at high institutes to ask them about TOPCon degradation points. Producers have additionally outlined the mitigation steps they’re taking.

Essential sources

On this first a part of a two-part sequence, we goal to contemplate any legitimate considerations for TOPCon producers.

Addressing these elements would require the trade to implement acceptable measures in an effort to mitigate the detrimental results that increased degradation sensitivity could entail. It’s apparent that TOPCon modules shouldn’t exhibit increased degradation ranges than right now’s market main PERC modules present over a 30-year lifespan below precise working circumstances – generally in relatively demanding environmental circumstances.

Any inherent higher-sensitivity related to the transition from PERC to TOPCon know-how must be clearly distinguished from any “teething pains” in newly launched TOPCon modules which were put in over the previous 18 months. The time period “teething pains” would characterize high quality points that come up when new applied sciences are launched to the market in “model 1.0” or even perhaps in a “model 0.9.” Such issues don’t essentially replicate a TOPCon-specific difficulty however relatively spotlight the truth that sure processes or supplies, as an example the encapsulants, have but to be absolutely optimized and fine-tuned to the precise wants of TOPCon cell know-how.

Expertise points with new merchandise usually are not distinctive to the photo voltaic trade. Some producers could merely be somewhat overly formidable to carry a product to market, most probably at a time when the total qualification and optimization steps of all related course of parameters in manufacturing haven’t been absolutely accomplished. Such an method successfully makes clients “beta testers” of the newly launched merchandise. Whereas this could be a viable improvement possibility for software program, we think about it detrimental for photovoltaic merchandise. In any case, a “bug repair” for photo voltaic modules usually can’t be applied by downloading a more recent model, as is customary for software program merchandise. If there’s a actual difficulty then, most of the time, the modules already put in within the area should be exchanged, which could be very pricey and time intensive.

As at all times, a superb status is well tarnished. It’s time-consuming and cumbersome to need to attempt to restore misplaced belief. It’s arduous to elucidate to clients that the “teething troubles” at present being noticed with some TOPCon suppliers usually are not issues inherent within the know-how however because of an absence of preparedness on the a part of some producers.

Simply as a prepare dinner can’t put together a three-star meal at their first or second try solely as a result of they’ve chosen one of the best substances, it seems logical that it’s unimaginable to launch a brand new cell kind onto market that meets all high quality necessities with out passing via a sure studying curve. Noting right here, after all, that the required lifespan is 30 years and extra.

The mandatory optimization routine equates to tweaking some course of parameters and figuring out viable course of home windows. Such fine-tuning can actually solely be achieved inside a framework of trial and error even when the producer has years of expertise in PERC manufacturing and was lucky sufficient to have chosen the right invoice of supplies (BoM) from the outset – which is an artwork in itself.

The PV trade continues to be below large value and price strain so producers at all times need to weigh how they put collectively the BoM for his or her modules; merely opting to at all times take one of the best elements obtainable is just not economically viable. In truth, very cautious consideration have to be given to any decision-making course of through which high-quality “substances” are deemed completely indispensable to create modules that can fulfil efficiency expectations over 30, 40, and even 50 years. It’s essential to determine the factors at which low value options could also be ample with out jeopardizing this purpose.

By way of the analysis performed by TNO within the Netherlands into sensitivity to sure forms of degradation in TOPCon cells, the researchers’ warnings middle on three areas:

1. Are TOPCon modules extra delicate to water vapor than PERC panels?

We all know that some producers have certainly taken additional precautions with respect to this degradation mechanism, stating that they attribute this increased sensitivity to the corrosion of the finely-porous glass that’s the “glass-frit” in modules. The corrosion reportedly happens because of chemical reactions between moisture/acetic acid and the silver-aluminum paste and glass frit.

Christos Monokroussos, from the testing lab TÜV Rheinland Shanghai, disagrees. “The sensitivity of PV modules to water vapor ingress is predominately managed by their encapsulation, and to a a lot lesser diploma by the cell know-how,” he says. “We don’t count on TOPCon modules to behave drastically completely different from typical PV modules in the case of water vapor ingress.”

As a takeaway, one can conclude that the chemical response that in the end results in corrosion, and thus degradation, is already well-known. So one would due to this fact assume that producers have taken this facet into consideration from the onset and have handled it via the right alternative of encapsulant.

2. Are TOPCon modules extra liable to UV degradation?

To this query, Monokroussos says, “Sure, TOPCon applied sciences exhibit an elevated sensitivity to UV radiation. The degradation is attributed to [issues with] floor passivation, which deteriorates after being uncovered to UV gentle. TÜV Rheinland is, due to this fact, designing an inner customary to deal with UV-induced degradation of TOPCon PV modules. Throughout this check, each faces of a PV module are uncovered to an elevated UV dose (10 occasions greater than acquired in IEC 61215 and IEC 61730 [standard testing conditions]), that are thought of ample to evaluate the susceptibility to UV-induced degradation.”

Monokroussos concludes that producers should due to this fact pay particular consideration to the right alternative of encapsulant. “Each the entrance glass and the encapsulant function a UV filter for the photo voltaic cells,” he says. “However since TOPCon cells are inherently extra delicate to UV degradation, and the UV filtering capabilities of the encapsulant decreases over time because the module is completely being uncovered to UV radiation, a extra UV resistant encapsulant must be chosen and, usually, a thicker layer of encapsulant is being thought of.”

3. PI Berlin’s Ukar says that TOPCon modules are extra delicate to potential-induced degradation polarization (PID-p). Is that this view shared by different specialists?

“Sure, n-type applied sciences, typically, are extra liable to PID-polarization,” confirms Monokroussos. “The degradation mode is mostly seen as reversible within the area so long as the module’s again facet is uncovered to UV gentle. Typically talking, in most software environments, PV modules would obtain some UV gentle from the again within the area but there could also be different software eventualities eg. roof-mounted installations, the place the rear facet doesn’t obtain ample UV irradiation, thus making these modules extra prone to extreme energy losses arising from PID-p. At the moment, the IEC [International Electrotechnical Commission] working group 2, which is the standardization group specializing in PV, is engaged on a process which might permit to determine the sensitivity of PV modules to PID-p.”

To summarize the three areas of concern, in all circumstances there are technological explanation why producers ought to pay additional consideration to those degradation paths. On the similar time, there are additionally options obtainable right now that don’t entail the numerous additional value to include these points.

If there are batches of TOPCon modules put in within the area that now exhibit issues, it’s rather more indicative of a producer releasing their product prematurely than an indication of an total downside related to TOPCon know-how.

It could be tempting to take a dismal outlook and surprise how lengthy it can take till all TOPCon producers have finally adjusted their BoMs and manufacturing processes to accommodate these current degradation threats. Nevertheless, we acquired one piece of suggestions from the analysis neighborhood that we imagine a lot better summarizes the outlook for the PV trade because it stands getting ready to transitioning from p-type wafers to n-type wafers.

Radovan Kopecek, from Worldwide Photo voltaic Power Analysis Heart Konstanz, factors out that whereas higher-efficiency cells might be prone to all types of degradation, n-type has inherent benefits.

“N-type materials is much less delicate to impurities and due to this fact degrades much less within the area – should you perceive what you might be doing within the course of,” says Kopecek. “In case you have the method below management and select a superb BoM (as an example, double glass and POE [polyolefin elastomer encapsulant]), new n-type module applied sciences shall be extra secure.

“Sadly, when know-how modifications happen too shortly, merchandise might be launched to the market too shortly,” Kopecek provides. “The worth strain within the trade is gigantic and at present the overcapacities created by the speedy expansions [of production fabs] is just not very useful. The trade should be taught to play a worldwide PV symphony and focus much less on solo virtuosity.”

Within the second installment of this sequence, we are going to evaluate and spotlight the completely different approaches being taken by the main TOPCon producers to deal with these challenges.