A thermoplastic encapsulant from Wacker, ‘TECTOSIL’, has proved to offer protection against potential-induced degradation (PID), according to tests carried-out by Photovoltaik-Institut Berlin. The testers confirmed that such modules do not display leakage currents due to PID when using the thermoplastic silicone elastomer sheet in the encapsulation of PV modules.

Problem

Potential-induced degradation (PID) is caused by undesired leakage currents on the cell surface. They cause negative charge carriers that would normally flow to the cell’s back contact to be discharged via the encapsulation and module frame, unused. Penetrating moisture and high module voltages promote this type of discharge, which can cause considerable performance losses. However, the PID effect is reversible and can be restricted through technical countermeasures.

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Solution

Measurements by the Photovoltaik-Institut Berlin have shown that such PID effects can be effectively suppressed, or prevented, with TECTOSIL encapsulant, which was tested as per IEC standard 60904-1 at a system voltage of 1,000 volts. The modules encapsulated with Wacker’s material showed no signs of PID, either in their voltage characteristics or during subsequent electroluminescence analysis.

Applications

Module encapsulation.

Platform

TECTOSIL is a flexible, highly transparent and electrically insulating sheet comprising an organosilicone copolymer. Because of its thermoplastic properties, the silicone-based polymer can be processed quickly and inexpensively – without curing or other chemical reactions, which facilitates short cycle times and a high tolerance to local temperature differences within the laminator. The sheet does not contain catalysts or corrosive substances. This allows for the encapsulating solar cells containing films of compound semiconductors or other highly sensitive chemical substances – such as transparent conductive oxides.