Carrier selective passivating contacts, which provide dual functions of surface defect passivation and
extracting one type of charge carriers, are the key enabler for realising the recent high efficiency Si solar cells. Here, I introduce two passivating contact materials developed in our lab: one is the hydrogenated nanocrystalline Si (nc-Si:H) and the other is the metal-oxidxe (non-silicon) materials.
For the nc-Si:H it is demonstrated that the use of the (p)nc-Si:H.instrinsic hydrogenated amorphous Si ((i)a-Si-H) stack instead of the conventional (p)a-SiH/(i)a-Si:H in silicon heterojunction solar cells provides not only a mitigation of the parasitic absorption loss but also improvements in passivation and electrical contact properties1. As a result, a record open-circuit voltage (754 mV) has been demonstrated by integrating (p)nc-Si:H/(i)a-Si:h contact in thin 9~50 um) Si solar cells2. Furthermore, a PV company has introduced similar technology and achieved a record efficiency among the whole Si solar cell architec-tures3. In the presentation, an optimum nc-Si:h nanostructure that leads to an improved solar cell per-formance will be outlined.
For metal-oxide material, a tunable carrier-selectivity behaviour is found in titanium oxide (TiOx) nanolayers (~5nm) grown directly on Si wafer by atomic layer deposition[4-6]. It is demonstrated that the TiOx acts as an efficient hole-selective passivating contact in Si solar cells with >20% efficiencies, which is antithetic to the previous understanding that TiOx acts solely as electron contact and hole blocker. The unique hole-selective feature of the TiOx has been investigated in collaboration with University of Oxford, and it is attributed to the creation of negative fixed charges at the TiOx/Si interface[4-6]. This new func-tionality of TiOx nanolayer opens opportunities for replacing the widelyused hetercontacts and dielectric-passivation layers in various types of Si solar cells.
Based on the above results, examples of applying the developed passivating contact materials (nc-Si:H)[7,8] and TiOx) as interconnection layers of the perovskite/Si tandem solar cells will be presented.
[1] H. Umishio et al., Prog. Photovolt. Res. Appl. 29, 344 (2021).
[2] H. Sai et al., Solar RRL 5, 2100634 (2021).
[3] H. Lin et al., Nat Energy 8, 789 (2023).
[4] T. Matsui et al., Sol. Energy Mater. Sol. Cells 209, 110461 (2020).
[5] T. Matsui et al. ACS Appl. Mater. Interfaces 12, 49777 (2020).
[6] T. Matsui et al., ACS Appl. Energy Materials, 5, 12782 (2022).
[7] C. McDonald et al., ACS Appl. Mater. Interfaces, 14, 33505 (2022).
[8] Y. Li et al., Adv. Mater. Interfaces, 2300504 (2023).
