Sprayed
transparent conductive oxides (TCOs) are an interesting
alternative to sputtered TCOs for many applications due to the possible
high throughput and a simple, atmospheric pressure process of spray
deposition. In this work, the growth mechanism of sprayed ZnO:In was
analyzed by transmission Kikuchi diffraction (TKD) analysis of the
thin film’s crystal orientation, which shows a preferred orientation
of the growing grains and thus proves that the deposition occurs from
the gas phase. It was observed that with increasing thickness of the
layer, the average grain size increases and the measured resistivity
significantly reduces to ≈5–6 × 10–3 Ω cm for layers of >500 nm thickness. Since many applications
also require good electrical contact formation, the contact resistivity
and the interface between sprayed IZO and n-type poly-Si and p-type
GaAs, two materials that are commonly used in III–V/silicon
tandem solar cells, were investigated by electrical measurements and
high-resolution transmission electron microscopy (TEM) analyses. The
interlayers observed in TEM were investigated by energy-dispersive
X-ray spectroscopy (EDS) line scans. The results suggest that oxidic
interlayers at the substrate/IZO interface are responsible for the
observed higher contact resistivity compared to the contact resistivity
of sputtered indium tin oxide (ITO) references. The results presented
in this work lead to a better understanding of the deposition process
occurring in spray pyrolysis and thus allow a more targeted optimization
of process parameters depending on the future requirements of the
application.
Herein, an analysis on the impact of laser contact opening of TOPCon/SiNx stacks is presented. By etching in tetramethylammonium hydroxide (TMAH), the defect distribution in the interfacial tunnel oxide is accessed and analyzed. The defect density is significantly increased in areas where adjacent laser contact openings (LCO) overlap. Using microscopic photoluminescence (μ‐PL) spectroscopy, it is verified that correlates with an increase in the local recombination rate and thus an increase in the J0,Met. Therefore, overlapping LCO of SiNx in TOPCon/SiNx stacks should be avoided as much as possible. Furthermore, the investigations indicate that defects in the interfacial oxide are dominantly created along exposed structures like tips and edges of (etched‐back) pyramids. A comparison of TOPCon/SiNx stacks with a variation of TOPCon thicknesses indicate that etch pits, and thus the defect density, related to LCO become more significant at lower thicknesses.
Herein, a novel strategy is introduced to reduce the consumption of scarce materials in silicon heterojunction solar cells by combining approaches for Ag replacement in the metallization and a reduction of the indium tin oxide layer thickness: a Ti layer deposited by physical vapor deposition serves both as the contact layer of a copper‐based metallization and after electrochemical oxidation as capping layer enabling the use of a thinner transparent conductive oxide. Further, the TiOx layer can build an encapsulation layer. While oxygen evolution and metal dissolution are found to be critical side reactions, a nonaqueous electrolyte is found in which these reactions can be avoided. The application on silicon heterojunction solar cells shows promising first results, exhibiting a short circuit current density of 35 mA cm−2 and a cell efficiency of close to 21% despite nonoptimized layer thicknesses.
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