SiNx and AlOx nanolayers in hole selective passivating contacts for high efficiency silicon solar cells

Journal article

The recombination of photogenerated charge carriers at metal-semiconductor interfaces remains a major source of efficiency loss in photovoltaic cells. Here, we present SiN x and AlO x nanolayers as promising interface dielectrics to enable high efficiency hole selective passivating contacts. It is demonstrated that SiN x deposited via direct plasma enhanced chemical vapour deposition can be grown controllably at thicknesses of 2 nm. The valence band offsets between crystalline silicon and ultrathin AlO x and SiN x nanolayers are measured as 3.5 and 1.4 eV, respectively. This predicts a larger tunnelling current for holes, compared to SiO x used typically. Resistivity measurements show that SiN x and AlO x nanolayers have lower contact resistivities compared to SiO x , with values as low as 100 mΩ·cm 2 . Analysis of the current transport mechanisms confirmed that tunnelling dominates the conduction through SiN x , while a mixture of tunnelling and pinholes are present in the AlO x structure. Lifetime measurements gave initial indications of the passivation quality of the films, with just 10 cycles of AlO x achieving 260 μ s after annealing and 1.9 ms with extrinsic field effect passivation added. Finally, the intrinsic built-in charge in the dielectrics was determined using surface photovoltage measurements and simulations are used to estimate the influence of nanolayer built-in charge in both poly-Si and dopant-free passivating contacts to enable future high efficiency solar cells.

Authors: McNab, S; Niu, X; Khorani, E; Wratten, A; Morisset, A

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: IEEE
• Journal: IEEE Journal of Photovoltaics
• Volume: 13
• Issue: 1
• Pages: 22-32
• Publication date: 2022-12-22
• DOI: 10.1109/jphotov.2022.3226706
• EISSN: 2156-3403
• ISSN: 2156-3381
• Language: English
• Keywords: FFR