Regionalizing Nitrogen Doping of Polysilicon Films Enabling High-Efficiency Tunnel Oxide Passivating Contact Silicon Solar Cells.

Tunnel oxide passivating contact (TOPCon) solar cells (SCs) as one of the most competitive crystalline silicon (c-Si) technologies for the TW-scaled photovoltaic (PV) market require higher passivation performance to further improve their device efficiencies. Here, the successful construction of a double-layered polycrystalline silicon (poly-Si) TOPCon structure is reported using an in situ nitrogen (N)-doped poly-Si covered by a normal poly-Si, which achieves excellent passivation and contact properties simultaneously. The new design exhibits the highest implied open-circuit voltage of 755 mV and the lowest single-sided recombination current density (J0 ) of ≈0.7 fA cm⁻2 for a TOPCon structure and a low contact resistivity of less than 5 mΩ·cm2 , resulting in a high selectivity factor of ≈16. The mechanisms of passivation improvement are disclosed, which suggest that the introduction of N atoms into poly-Si restrains H overflow by forming stronger Si-N and N-H bonds, reduces interfacial defects, and induces favorable energy bending. Proof-of-concept TOPCon SCs with such a design receive a remarkable certified efficiency of 25.53%.

Novel polysilicon in resisting thermal-evaporation Al-electrode damage and its application in back-junction passivated contact p-type solar cells.

In preparing tunnel oxygen passivation contact (TOPCon) solar cells, the metallization process often causes damage to passivation performance. Aiming to solve the issue, we investigated the advantages of the novel polysilicon, i.e. the carbon (C) or nitrogen (N) doped polysilicon, in resisting metallization damage. Our study reveals that C- or N-doped polysilicon does mitigate the passivation damage caused by the physical-vapor deposition metallization processes, i.e. the decrease in implied open-circuit voltage (iVoc) and the increase in recombination current (J0) are both suppressed. For the novel polysilicon samples suffered metallization, the decrease ofiVocwas only ∼-1 mV, and the increase ofJ0< 1 fA cm-2; in contrast, the decrease ofiVocof the standard polysilicon samples was -7 mV, and the increase ofJ0was ∼6 fA cm-2. In addition, we also explored the difference between the finger-metal and the full-metal metallization, showing that the finger-metal has less passivation damage due to the smaller contact area. However, the free energy loss analysis indicates that the advantage of the novel polysilicon in resisting metallization damage is overshadowed by the disadvantage of the higher contact resistivity when finger-metal electrodes are used. Numerical simulations prove that the efficiency of the solar cell with novel polysilicon still shows >0.2% absolute efficiency higher than that with the standard polysilicon, reaching 26% when full-metal electrodes by thermal evaporation.

50-µm thick flexible dopant-free interdigitated-back-contact silicon heterojunction solar cells with front MoOx coatings for efficient antireflection and passivation.

We demonstrate experimentally a flexible crystalline silicon (c-Si) solar cell (SC) based on dopant-free interdigitated back contacts (IBCs) with thickness of merely 50 µm for, to the best of our knowledge, the first time. A MoOx thin film is proposed to cover the front surface and the power conversion efficiency (PCE) is boosted to over triple that of the uncoated SC. Compared with the four-time thicker SC, our thin SC is still over 77% efficient. Systematic studies show the front MoOx film functions for both antireflection and passivation, contributing to the excellent performance. A double-interlayer (instead of a previously-reported single interlayer) is identified at the MoOx/c-Si interface, leading to efficient chemical passivation. Meanwhile, due to the large workfunction difference, underneath the interface a strong built-in electric field is generated, which intensifies the electric field over the entire c-Si active layer, especially in the 50-µm thick layer. Photocarriers are expelled quickly to the back contacts with less recombined and more extracted. Besides, our thin IBC SC is highly flexible. When bent to a radius of 6 mm, its PCE is still 76.6% of that of the unbent cell. Fabricated with low-temperature and doping-free processes, our thin SCs are promising as cost-effective, light-weight and flexible power sources.