Tantalum Oxide Electron-Selective Heterocontacts for Silicon Photovoltaics and Photoelectrochemical Water Reduction

Abstract

Crystalline silicon (c-Si) solar cells have been dominating the photovoltaic (PV) market for decades, and c-Si based photoelectrochemical (PEC) cells are regarded as one of the most promising routes for water splitting and renewable production of hydrogen. In this work, we demonstrate a nanoscale tantalum oxide (TaO x , ∼6 nm) as an electron-selective heterocontact, simultaneously providing high-quality passivation to the silicon surface and effective transport of electrons to either an external circuit or a water-splitting catalyst. The PV application of TaO x is demonstrated by a proof-of-concept device having a conversion efficiency of 19.1%. In addition, the PEC application is demonstrated by a photon-to-current efficiency (with additional applied bias) of 7.7%. These results represent a 2% and 3.8% absolute enhancement over control devices without a TaO x interlayer, respectively. The methods presented in this Letter are not limited to c-Si based devices and can be viewed as a more general approach to the interface engineering of optoelectronic and photoelectrochemical applications.

Tantalum Nitride Electron‐Selective Contact for Crystalline Silicon Solar Cells

“…However, by using the TaN x contact, we obtain a device with a higher FF and a comparable www.advenergymat.de www.advancedsciencenews.com V oc , resulting in a slightly higher efficiency than that of singlelayer TiO 2 and TaO x contacts (see Table S1, Supporting Information). [16][17][18]25] These results indicate that the low contact resistivity and moderate surface passivation of the TaN x heterocontact can be maintained on the device. From the HRTEM image of the Si/TaN x /Al interface, shown in Figure 6b, we can also conclude that no interlayer has been formed at the interfaces, and that no intermixing has occurred with either Si or Al, indicating a high stability of the TaN x heterocontact.…”

“…The quality of passivation of the TaN x films on silicon surface is quantified in terms of effective carrier lifetime (τ eff ) using the quasi-steady state photoconductance (QSSPC) technique. However, the surface passivation of these TaN x layers is poorer than the passivation obtained by TiO 2 and TaO x films [17,25] but may be improved by a further optimization of the deposition process. An ultrathin TaN x interlayer (1.0 nm) can reduce S eff from ≈10 6 -10 7 (Si/Al direct contact) to ≈390 cm s −1 .…”

Exploring co-sputtering of ZnO:Al and SiO2 for efficient electron-selective contacts on silicon solar cells

“…have attracted a significant interest as these contacts have the potential to further improve the cell performance by using more transparent or conducting layers, and to simplify the fabrication process. Until now, various materials have been demonstrated as effective electron-selective layers, including LiFx [8], MgFx [9], MgOx [6], TiOx [4,5], TaOx [11], TaNx [10], alkali/alkaline-earth metal carbonates [12], and their combinations [13], in some cases combined with intrinsic a-Si:H (i a-Si:H) for passivation.…”

Dopant‐Free Back‐Contacted Silicon Solar Cells with an Efficiency of 22.1%

“…Materials used so far as dopant‐free carrier‐selective contacts include hole‐selective molybdenum oxide (MoO x ), tungsten oxide (WO x ), vanadium oxide (V 2 O x ), chromium oxide (CrO x ), electron‐selective lithium fluoride (LiF x ), tantalum oxide (TaO x ), titanium dioxide (TiO 2 ), magnesium fluoride (MgF x ), magnesium oxide (MgO x ), magnesium (Mg), and calcium (Ca) . The key issue is to optimize the trade‐off between contact resistivity and recombination of charge carriers at the hole‐ and electron‐selective contacts .…”

“…The key issue is to optimize the trade‐off between contact resistivity and recombination of charge carriers at the hole‐ and electron‐selective contacts . Recently, a promising strategy to improve the selectivity of contacts is to use multilayer films such as TiO 2 /Ca, Al 2 O 3 /TiO 2 /Mg, and TaO x /Mg covered with Al as the electrode, which has been demonstrated to yield a reduced contact resistivity and recombination losses at the heterointerface with c‐Si, presumably with little influence from this second capping metal.…”