Metal-induced gap states in passivating metal/silicon contacts

Abstract

Passivating metal/silicon contacts combine low carrier recombination with low contact resistivities, enabled by a low gap state density at their interface. Such contacts find applications in high-efficiency solar cells. We perform first-principles calculations based on density functional theory to investigate the surface defect and metal-induced gap state density of silicon in close contact with metals (Al and Ag). We confirm that surface hydrogenation fully removes surface-defect gap states of (111)-oriented silicon surfaces. However, the metal-induced gap state density increases significantly when metals are closer than 0.5 nm to such surfaces. These results highlight the importance of the tunneling-film thickness in achieving effective passivating-contact formation.

Modeling of surface gap state passivation and Fermi level de-pinning in solar cells

“…The role of MIGS in FLP in PVs was recently briefly covered by Robertson [14] and in recombination by Sajjad et al [15]. These effects are now confirmed by more detailed density function supercell calculations.…”

A universal solution processed interfacial bilayer enabling ohmic contact in organic and hybrid optoelectronic devices

“…42 This electrical barrier can be overcome by the introduction of very thin (o10 nm) layer between PCBM and metal, with metal oxides and organic small molecules being common choices aimed at reducing the defect and metal induced gap state density, between metal and semiconductor, which causes FLP. 6 A simple and accessible method to probe the ohmic contact at this interface is to fabricate so-called 'electron-only' devices with different interfacial layers. Fig.…”

“…Passivation layers, both organic and inorganic, have also been studied which suppress recombination and enhance carrier selectivity. [4][5][6] In the case of OLEDs and organic photovoltaics (OPVs), thermally evaporated inorganic materials including MoO 3 and V 2 O 5 , as well as Ca and LiF, have been employed as hole-transport and electron-transport layers (HTL and ETL), respectively. 7 These materials are widely utilized owing to their suitable work functions and, depending on the device structure, optical transparency.…”

“…Conversely, electrode-surface modification treatments are favored in OFET devices, an example being the pre-treatment of a gold electrode with pentafluorothiophenol (PFBT) prior to the deposition of an organic semiconductor with a low lying highest occupied molecular orbital (HOMO). [13][14][15] In the short time since their introduction, so-called 'inverted', p-i-n structured perovskite solar cells have employed a wide range of cathode interfacial layers (CILs): typically, fullerene C 60 or [6,6]phenyl-C 61 -butyric acid methyl ester (PCBM) are inserted between perovskite and evaporated metal electrodes as ETLs. [16][17][18][19] However, the tendency of fullerene materials' to form a non-ohmic contact with these electrodes requires the presence of an additional interlayer to nullify the barrier formed at this interface.…”

Recombination junctions for efficient monolithic perovskite-based tandem solar cells: physical principles, properties, processing and prospects

“…In silicon, for example, FLP is a significant impediment in forming carrier-selective contacts via direct metallization, owing to the presence of a high concentration of surface defects (silicon dangling bonds), as well as metal-induced gap states. 53 These defect-and metal-induced gap states (DIGS and MIGS) limit the ability of the overlying metal workfunction to manipulate the surface potential of c-Si, impairing charge-selectivity ( Fig. 3b).…”