Low contact resistivity (ρ c ) and low recombination current density at the metallized area (J 0,metal ) are the key parameters for an electron-selective contact in solar cells, and an i-a-Si:H/TiO x /low work function metal (ATOM) structure could satisfy these criteria. In this work, to achieve strong downward band bending, an Yb (Φ = 2.5−2.6 eV)/Ag stack is used. Moreover, the impact of (1) substrate topography (flat or textured), (2) TiO x thickness, and (3) Ti precursor (TTIP vs TDMAT) on the ATOM contact performance is investigated. The results show that the ATOM contact is relatively insensitive to the surface topography and to the Ti precursors (TTIP or TDMAT) used for the atomic layer deposition (ALD) of TiO x . However, the TiO x thickness has a significant impact on the ρ c and marginally on the J 0,metal of the ATOM contact. For all topography cases and Ti precursors, 1 nm thick TiO x results in the lowest ρ c value, most likely due to E F,metal depinning. In the silicon heterojunction solar cell, this ATOM contact (i-a-Si:H/TiO x /Yb/Ag) yields a solar cell efficiency of 19.2% with a high V OC of 723 mV without the need of a doped n-a-Si:H layer. Concerning the thermal stability of these contacts, TEM images confirm that Yb does not diffuse into the i-a-Si:H layer after an annealing at 180°C for 30 min thanks to the TiO x layer behaving as a diffusion barrier. 98% of the initial solar cell efficiency is preserved even after successive annealing treatments at 150 and 175°C, which are values in the same temperature range used in the module lamination and the sintering of the printed Ag. These results in combination with the demonstrated efficiency underline that the ATOM contact is a promising route to realize high-efficiency solar cells.

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Highlights• MoOx is used to replace p-a-Si:H at the hole contactin silicon heterojunction (SHJ) solar cells, leading to a reduction of parasitic absorption and a JSC improvement on average of 0.5 mA/cm 2 .• Influence of MoOx thickness and annealing condition on the SHJ cell performance was studied and optimal parameters were determined.• Impact of MoOx thickness and anneal treatment on the thin film interfaces at the hole contact was investigated and an interfacial dipole in the form of a-SiOx was postulated.• A glass to glass 1-cell mini-module was fabricated using a MoOx-contacted SHJ cell.• After damp-heat testing, good long-term stability was achieved at module-level, with a degradation of less than 3%abs (passing the IEC61215 standard).

We report on the optical and electrical performances of periodic photonic nanostructures, prepared by nanoimprint lithography (NIL) and two different etching routes, plasma, and wet chemical etching. Optically, these periodic nanostructures offer a lower integrated reflectance compared with the industrial state-of-the-art random pyramid texturing. However, electrically, they are known to be more challenging for solar cell integration. We propose the use of wet chemical etching for fabricating inverted nanopyramids as a way to minimize the surface recombination velocities and maintain a conventional cell integration flow. In contrast to the broadly used plasma etching for nanopatterning, the wet chemically etched nanopatterning results in low surface recombination velocities, comparable with the state-of-the-art random pyramid texturing. Applied to 40-μm thick epitaxially grown crystalline silicon foils bonded to a glass carrier superstrate, the periodic-inverted nanopyramids show carrier lifetimes comparable with the non-textured reference foils (τ eff = 250 μs). We estimate a maximum effective surface recombination velocity of~8 cm/s at the patterned surface, which is comparable with the state-of-the-art values for crystalline silicon solar cells.

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Previously, IMEC proposed the i 2-module concept which allows to process silicon heterojunction interdigitated back-contact (SHJ-IBC) cells on thin (<50 µm) Si wafers at module level. This concept includes the bonding of the thin wafer early on to the module cover glass, which delivers mechanical support to the wafer and thus significantly improves the production yield. In this work, we test silicone and EVA bonding agents and prove them to be resistant to all rear side processes, including wet and plasma processes. Moreover, a lift-off process using a sacrificial SiOx layer has been developed for emitter patterning to replace conventional lithography. The optimized process steps are demonstrated by the fabrication of SHJ-IBC cells on 6-inch 190 µm-thick wafers. Efficiencies up to 22.6% have been achieved on reference freestanding wafers. Excellent Voc of 734 mv and Jsc of 40.8 mA/cm 2 lead to an efficiency of 21.7% on silicone-bonded cells, where the high Voc indicates the process compatibility of the bonding agent. The developments that enabled such achievements and the key factors that limit the device performance are discussed in this paper.