Plasma–silicone interaction during a-Si:H deposition on solar cell wafers bonded to glass

• Published in: Solar energy materials and solar cells Vol. 124; pp. 48 - 54
• Main Authors: Granata, Stefano Nicola, Boulord, Caroline, Govaerts, Jonathan, Bearda, Twan, Beaucarne, Guy, Soogund, Deana, Pérez, Raquel Vaquer, Dross, Frederic, Abdulraheem, Yaser, Poortmans, Jef, Mertens, Robert
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.05.2014; Elsevier
• Subjects: Amorphous silicon; Applied sciences; Bonding; Degradation; Deposition; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Energy; Exact sciences and technology; FTIR; Glass; Lifetime; Natural energy; Outgassing; Photoelectric conversion; Photovoltaic cells; Photovoltaic conversion; Silicone; Solar cells; Solar cells. Photoelectrochemical cells; Solar energy; Surface passivation; Wafer bonding; Wafers; Wafer bonding; Amorphous silicon; Lifetime; FTIR; Surface passivation; Silicone; Amorphous material; Glass; Coatings; Degradation; Degassing; Charge carrier recombination; Adhesive joint; Silicon; Fourier-transformed infrared spectrometry; Adhesive; Siloxane polymer; Wafer; Damaging; Passivation; Durability; Plasma interactions; Open circuit voltage; Surface treatment; Solar cell; Thickness; Surface recombination; Amorphous hydrogenated material
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2014.01.035

A scenario for future silicon photovoltaics is to use wafer-based solar cells with a thickness below 100μm. A way to realize this scenario is the merging of cell and module processing, with thin wafers processed while attached to the superstrate glass. One of the challenges for this type of processing is the achievement of high performing surface passivation, i.e., with surface recombination velocities below 10cm/s. In this paper, a detailed explanation for lifetime degradation on wafers bonded to glass by means of silicone is proposed. The degradation is due to cyclic silicone molecules outgassing during a-Si:H deposition from the adhesive used to bond the wafers. The cyclic molecules are incorporated in the a-Si:H layer and modify the amorphous silicon network. By the application of specific outgassing conditions before a-Si:H deposition, a significant amount of cyclic molecules is removed from the adhesive. Non-degraded a-Si:H layers and surface passivation comparable to standalone wafers are obtained, as shown with measures of lifetime and solar cell open circuit voltage. •Silicone can outgas cyclic chains of low molecular weight.•The outgassed chains can be incorporated into the aSi:H passivation layer.•aSi:H passivation of bonded wafer is degraded by silicone outgassing.•An additional outgassing prior to passivation removes the harmful molecules.•Comparable lifetimes and Voc are obtained on standalone and bonded solar cells.