• Energy Research

Abstract The use of Ti phosphate as a functional coating for Li ion battery electrodes has been investigated, as well as the effect of nitrogen doping on its electrochemical properties. First, previous knowledge on PE-ALD of Ti phosphate (using an exposure sequence of trimethylphosphate plasma–oxygen plasma–titaniumisopropoxide) was used to study an altered process using a nitrogen plasma, i.e. TMP* - N2* - TTIP. This enabled the deposition of a nitrogen doped (6 at.%) Ti phosphate with a growth per cycle of 0.4 nm/cycle. Next, a dual-source precursor (diethylphosphoramidate plasma, or DEPA*) was introduced instead of TMP*, allowing for a higher growth rate (0.6 nm/cycle) and a higher nitrogen level (8.6 at.%). The ionic transparency of the phosphate slightly decreased due to nitrogen incorporation, but the effective transversal electronic conductivity showed to be three times higher after nitrogen doping. A 2 nm coating of (un)doped Ti phosphate significantly improved the rate capability of a lithium nickel manganese cobalt oxide (NMC) electrode, increasing the amount of energy that can be stored at high (dis)charging speeds with a factor 10 (at 5C). In addition, the undoped titanium phosphate coating offered increased stability, retaining 84% of the capacity after 100 cycles at 1C with respect to 79% for the uncoated electrode.

ABSTRACTDriven by the relatively high cost of silver (Ag), interest has grown in the photovoltaic (PV) industry to substitute conventional screen printed (SP) Ag front contacts with copper (Cu) plated contacts. The approach chosen here applies selective laser ablation of the front anti‐reflection coating (ARC), then forming self‐aligned nickel silicides (NiSix) contacts, and thickening the lines by Cu plating to achieve the desired line conductivity. A successful implementation of this scheme requires annealing to form NiSix with low contact resistance. However, it has been shown that industrial shallow emitters can be damaged severely upon conventional annealing of nickel. In this paper, we show that by using large area excimer laser annealing (ELA), NiSix contacts can be formed on industrial shallow emitters without the associated junction degradation. On the basis of sheet resistance, transmission electron microscopy, and lifetime measurements, we demonstrate that NiSix formation by ELA can be achieved in narrow contact openings without damaging the passivation and reflectance properties of the neighboring ARC. In addition, the thresholds for NiSix formation for different Ni thicknesses are quantified by rigorous finite element simulations and compared with experimental data. Finally, high efficiency passivated emitter and rear cell type solar cells featuring a shallow 85 Ω/sq emitter have been processed on large area CZ–Si using laser ablation of the ARC and subsequent NiSix formation by ELA. These cells show an average efficiency gain of 0.4%abs compared with cells processed with reference SP contacts. In this work, the best performing cell with the ELA process reached 20.0% energy conversion efficiency. Copyright © 2013 John Wiley & Sons, Ltd.

AbstractThis work focuses on the mechanisms of alkaline electroless Ni deposition on n-type Si substrates and silicide formation by rapid thermal treatment. The deposited Ni layers were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS), and electron energy loss spectroscopy (EELS). The results indicate that Ni deposition occurs in two steps; a nucleation step, dominated by electrochemical processes, followed by autocatalytic deposition of Ni involving the reducing agent NaH2PO2. The oxygen content was found to be uniform in the Ni layer and was higher close to the Si/metal interface. The silicide formation from alkaline Ni deposits was characterized by 4 point probe measurements, in-situ x-ray dispersion (XRD) measurements, and TEM measurements. Results were compared to silicides formed from ‘pure’ sputtered Ni layers. It was observed that the silicide-formation temperature is higher for an electroless Ni layer than that for a sputtered Ni layer. The results suggest that the temperature ramping rate influences crystallographic phase formation.