Research exhibits n-type bifacial TOPCon cells extra liable to degradation than p-type

April 27, 2023 Emiliano Bellini

Researchers on the Netherlands Organisation for Utilized Scientific Analysis (TNO) have carried out a collection of damp warmth exams to evaluate the affect, by way of moisture degradation, of various encapsulation supplies on efficiency losses in bifacial PV modules.

“The aim of this analysis was to search out an evidence for degradation phenomena noticed in small laboratory bifacial module samples after prolonged damp warmth testing,” the analysis’s lead writer, Paul Sommeling, informed pv journal.

Within the examine “Corrosion results in bifacial crystalline silicon PV modules; interactions between metallization and encapsulation,” printed in Photo voltaic Power Supplies and Photo voltaic Cells, the scientists made a comparability between three encapsulant supplies utilized in PV module manufacturing: ethylene vinyl acetate (EVA), polyolefin elastomers (POE) and thermoplastic polyolefins (TPO).

The analysis group stated it noticed in earlier research that POE and TPO, in contrast to EVA, don’t launch any acidic parts, which implies they could carry out higher than EVA with respect to acid-induced corrosion. Nonetheless, there isn’t any confirmed proof but that these supplies may very well lead to elevated module sturdiness within the area, because it takes a very long time earlier than related area degradation may be noticed.

By way of damp warmth testing with a period of as much as 2,500 h, the teachers in contrast the efficiency of the three supplies in glass-encapsulant-cell-encapsulant-glass-based laminates with out the usage of an edge sealant.

“Commercially out there n- or p-type bifacial cells (TOPCON and PERC respectively) have been used to construct these laminates, which have subsequently been examined in a local weather chamber underneath damp warmth situations (85 C/85% relative humidity),” they defined. “Present-voltage (IV) and electroluminescence (EL) measurements have been carried out at 500 h intervals to observe the change of laminate traits over time.”

They used a method generally known as “coring” to allow autopsy analyses of all samples examined. For this, they used scanning electron microscopy (SEM) and Power-dispersive X-ray spectroscopy (EDX) to research the results of the exams on the photo voltaic cell floor. All encapsulants have been examined in keeping with the IEC 61215 PV commonplace and past, with prolonged testing time.

In accordance with the analysis group, the testing confirmed that hydrophobic and chemically inert TPO encapsulants offered the very best diploma of safety towards moisture-induced degradation in comparison with EVA and POE. It additionally indicated that front-side metallization of the n-type TOPCon cells examined is extra liable to acid- or moisture-induced degradation than their p-type counterparts.

“This front-side metallization of TOPCon cells degraded sooner than the rear-side metallization and likewise sooner than the metallization of PERC cells in EVA-based laminates,” the scientists emphasised. “We attribute these variations to the totally different compositions of the cell metallization utilized.”

They concluded that the principle issue inflicting delamination of the steel grid is the degradation of lead glass most likely, which they stated is a part of the cell metallization grid and incorporates lead oxide (PbO). 

“These outcomes are partly shocking,” Sommeling stated. “Corrosion results in PV are identified and have been reported within the literature learning each the results after area publicity and after accelerated testing within the laboratory.”

He additionally defined that essentially the most extreme corrosion issues are to a big extent associated to the discharge of acetic acid from EVA, essentially the most extensively used encapsulating materials in PV panels. The acid causes corrosion of cell metallization and/or tabbing materials or solder joints. Presently, EVA is being changed by options that don’t launch any acidic compounds and this helps to stop plenty of issues associated to corrosion.

“The shocking or ‘new’ elements described in our paper contemplate the fairly placing variations noticed between various kinds of metallization and totally different photo voltaic cells with respect to corrosion conduct, which may be correlated to totally different compositions of the cell metallization,” Sommeling added. “Additionally with out acids current, corrosion nonetheless can happen simply by the affect of moisture and once more that is extensively various between the various kinds of metallization utilized.”

“It may be concluded that the particular mixture of the n-type TOPCon photo voltaic cells studied in our paper together with EVA might be a better threat one, in comparison with different combos of cell sorts and encapsulants,” Sommeling affirmed. “Utility of EVA together with comparatively excessive corrosion vulnerable metallization ought to and might truly be averted. Alternatively, if the extra corrosion-resistant metallization sorts recognized may be utilized to TOPCon photo voltaic cells, this also needs to assist in constructing extra corrosion-resistant n-type PV panels.”