Improved Performance of Titanium Oxide/Silicon Oxide Electron‐Selective Contacts by Implementation of Magnesium Interlayers

Abstract

The impact of the implementation of magnesium interlayer and the layer thickness (tTiOx) of titanium oxide on the electrical properties of TiOx/SiOy/Si heterojunctions is investigated to improve electron transport for use in silicon heterojunction solar cells. The passivation performance is improved with increasing tTiOx. For the samples with Mg interlayer, ohmic contact can be attained for the thicker TiOx layer compared with the sample without Mg interlayer. Schottky contact is mitigated by the TiOx/SiOy stacking layers and Mg interlayer, attributed to the reduction of interfacial energy level by TiOx/SiOy stacking layers and enhanced downward band bending by Mg interlayer. The open‐circuit voltage and fill factor of the solar cells are improved by inserting the TiOx/SiOy stack and the Mg interlayer, indicating that the electron selectivity is enhanced. Excellent surface passivation and transport properties can be achieved by controlling TiOx layer thickness and using the Mg interlayer.

Optimization of a Solution-Processed TiOx/(n)c-Si Electron-Selective Interface by Pre- and Postdeposition Treatments

“…The attained low contact resistivity is also owing to both chemical and field-effect mechanisms, which can be construed as follows: (i) Chemical passivation screens the dangling bonds and trap states at the interface hindering Fermi-level pinning, even in the absence of LiF x interlayer. (ii) It is well-known that TiO x with a higher concentration of Ov yields higher conductivity and thus lower ρ c . ,,, The overlaying metal can affect the TiO x composition, which indeed depends on the metal work function. , The redox reaction of TiO x enhances when it comes in contact with a low WF overlayer, leading to a reduction in ρ c . ,, (iii) Meanwhile, as probed by AFM (Figure S4b), longer annealing time coincides with the development of valleys or pinholes, which, first, promotes current flow through defect-assisted tunneling and, second, facilitates LiF x diffusion in the TiO x underlay, evoking energy states close to the conduction and/or valence bands of TiO x and thus exciting its conductivity . Because of the aforementioned reasons, we observed a lower ρ c as LiF x and/or a longer annealing duration was employed (see Figure c).…”

Quantitative evaluation of implied open-circuit voltage after metal electrode deposition on TiO x /Si heterostructures by photoluminescence imaging: impact of metallization on passivation performance

“…The Mg electrode was employed to reduce the contact resistance. 34) After each process, the iV OC and I PL (PL intensity per unit second) of the fabricated samples were measured by the QSSPC system (WCT-120TS, Sinton Instrument Inc.) and the PL imaging system (EPL-100s, Hamamatsu Photonics), respectively. After metal electrode deposition, only I PL was measured.…”

“…31) To solve the former issue, the attempts that use low-work function materials are made to introduce downward band bending. In fact, there are some reports to lower the contact resistivity by inserting low-work function materials such as LiF, 32) Ca, 33) and Mg. 34) On the other hand, the latter issue has not been addressed yet, and the degradation mechanism has not been fully understood. Therefore, mitigating the metallization-induced degradation is essential to use TiO x as an ESC in practical Si solar cells.…”

Dopant‐free passivating contacts for crystalline silicon solar cells: Progress and prospects

“…Compared to other metals (Ni, Al), one sees from the J‐V curves (Figure 9B) that the cell performance gradually deteriorates as the metal W F increases. In addition, in the c ‐Si solar cells employing TiO x ‐based passivating contact, a Mg interlayer between TiO x and Al can enhance the downward band bending of c‐ Si, which efficiently increases the tunneling probability of electrons and mitigates the non‐Ohmic behavior 211 . Noteworthily, some other thin alkali/alkaline‐earth metal salts, such as LiF, can lower the W F of electrode, 50,63,172 which effectively improves the electron transport and decreases the ρ c .…”

“…In addition, in the c-Si solar cells employing TiO x -based passivating contact, a Mg interlayer between TiO x and Al can enhance the downward band bending of c-Si, which efficiently increases the tunneling probability of electrons and mitigates the non-Ohmic behavior. 211 Noteworthily, some other thin alkali/alkaline-earth metal salts, such as LiF, can lower the W F of electrode, 50,63,172 which effectively improves the electron transport and decreases the ρ c . Taking Al electrode as an example, unlike the ρ c reduction probably resulting from the interfacial mixing in the abovementioned TiO x /LiF stack, 49 55 Copyright 2021, American Chemical Society 540 to 26 mΩÁcm 2 , greatly improving the hole transport of contacts.…”