Passivating electron‐selective contacts for silicon solar cells based on an a‐Si:H/TiO x stack and a low work function metal

• Published in: Progress in photovoltaics 2018-10, Vol.26 (10), p.835-845
• Main Authors: Cho, Jinyoun, Melskens, Jimmy, Debucquoy, Maarten, Recamán Payo, Maria, Jambaldinni, Shruti, Bearda, Twan, Gordon, Ivan, Szlufcik, Jozef, Kessels, W.M.M., Poortmans, Jef
• Format: Article
• Language: English
• ISSN: 1062-7995; 1099-159X
• DOI: 10.1002/pip.3023

In this work, the ATOM (intrinsic a‐Si:H/TiO x /low work function metal) structure is investigated to realize high‐performance passivating electron‐selective contacts for crystalline silicon solar cells. The absence of a highly doped Si region in this contact structure is meant to reduce the optoelectrical losses. We show that a low contact resistivity ( ρ c ) can be obtained by the combined effect of a low work function metal, such as calcium (Φ 2.9 eV), and Fermi‐level depinning in the metal‐insulator‐semiconductor contact structure (where in our case TiO x acts as the insulator on the intrinsic a‐Si:H passivating layer). TiO x grown by ALD is effective to achieve not only a low ρ c but also good passivation properties. As an electron contact in silicon heterojunction solar cells, inserting interfacial TiO x at the i‐a‐Si:H/Ca interface significantly enhances the solar cell conversion efficiency. Consequently, the champion solar cell with the ATOM contact achieves a V OC of 711 mV, FF of 72.9%, J SC of 35.1 mA/cm 2 , and an efficiency of 18.2%. The achievement of a high V OC and reasonable FF without the need for a highly doped Si layer serves as a valuable proof of concept for future developments on passivating electron‐selective contacts using this structure.