Lithium-doped Nickel Oxide Grown by Different PVD Methods for Hole-Selective Contact in Silicon-Based Heterojunctions

Carrier-selective contacts are well known to be one of the keys to obtain cost effective high-efficiency solar cells. In silicon-based heterojunctions the contacts are usually obtained by doped hydrogenated amorphous-silicon (a-Si:H) layers, which however introduce important absorption losses and require expensive production processes. Many candidate materials have been identified to substitute a-Si:H layers, but their full exploitation is frequently limited by the constrain of being resistant to thermal treatments up to at least 250°C. Among them, doped nickel oxide seems to be ideal to form a hole-selective contact thanks to the alignment of its valence band with that of silicon. In this work we grew films of lithium-doped nickel oxide (NiOx:Li) by different PVD techniques and tested their behavior in holeselective contacts in silicon heterojunctions. The J-V characteristics of the proof-of-concept devices demonstrate the possibility to replace p-type a-Si:H film with NiOx:Li, although further improvements are needed to optimize the performances and solve the issue related to silicon lifetime degradation.