Low Work Function Ytterbium Silicide Contact for Doping-Free Silicon Solar Cells

Abstract

Metal silicide is a well-known material for contact layers, however, it has not been tested in the context of doping-free carrier selective contacts. Thin film deposition of an appropriate metal with mild annealing treatment is an interesting alternative to the more complex depositions of other compound materials. Reaction of Yb deposited on top an i-a-Si:H passivation layer results in the formation of YbSix on top of a remnant i-a-Si:H following a low-temperature anneal below 200 °C. Such a contact is an interesting candidate as a doping-free electron-selective contact. Detailed investigation of the i-a-Si/YbSix contact shows that Yb thickness, i-a-Si:H thickness and silicidation annealing conditions play a significant role in determining the recombination current density (J0,metal) and the contact resistivity (ρc). Low J0,metal of 5 fA/cm 2 and low ρc below 0.1 Ω.cm were independently demonstrated for such ia-Si:H/YbSix contacts. We also demonstrate that low-temperature silicidation can be combined with

Modulation Doping of Silicon Nanowires to Tune the Contact Properties of Nano‐Scale Schottky Barriers

“…This effect has been reported to be very prominent for metal silicides. [ 39 ] Modulation doping creates similar surface states in silicon due to the electron capture process and thus influences the interface between the silicide and silicon. As a result, the NiSi x work function is strongly pinned to the Fermi level near the valence band resulting in an Ohmic‐type contact as observed for the high modulation doping of silicon.…”

A High-Quality Dopant-Free Electron-Selective Passivating Contact Made from Ultra-Low Concentration Water Solution

“…The Al directly contacted heterojunction solar cell shows poor performance as the V oc , J sc , FF, and PCE are 375 mV, 37.5 mA·cm −2 , 51.6%, and 7.3%, respectively. The a-Si:H(i)/Al direct contact is not a good idea [ 14 , 43 , 44 ] as the metal atoms can easily diffuse through the thin a-Si:H layer and destroy the passivation [ 14 , 45 ]. The a-Si:H(i)/TX-100/Al contact demonstrates good performance, showing V oc close to 700 mV and the champion PCE of 20.4%, which is significant in similar investigations [ 25 , 27 ].…”

Temperature and environmentally stable titanium carbide as an electron-selective heterocontact for crystalline silicon solar cells

“…Recently, transition metal oxides (TMOs) and alkali metal fluorides have been widely investigated as electron-selective contact (ESC) materials, forming excellent Ohmic contacts to the lightly doped n-type c-Si with mΩ cm 2 scale contact resistivities. 8–38 The studies of ESC materials have further extended to low-work-function alkali or alkaline earth metals, 39,40 transition metals, 22 and their compounds such as halides, 36,41 oxides, 14,42,43 nitrides, 28,29 sulfides, 30,44 silicides, 45 carbonates 46 as well as organic compounds. 47,48 As a result, c-Si solar cells with dopant-free ESC have exhibited a high conversion efficiency beyond 23%.…”

“…Yb-based silicide ESCs have demonstrated good thermal stability, maintaining contact resistivity even after post-annealing at 180 °C. 45 The other candidate for thermal stability is alkaline earth metal acetylacetone (Acac). Solar cells with c-Si(n)/a-Si:H(i)/CaAcac/Al ESC are thermally stable in forming gas for 10 min at 300 °C without efficiency degradation.…”