XIS: A Low-current, High-voltage Back-junction Back-contact Device

AbstractIn this paper we present experimental results of a low-current, high-voltage back-junction back-contact device. The concept is demonstrated by the successful transformation of finished IBC cells into XIS (Crystalline Silicon Interconnected Strips) devices, leading to 8.5V for a series connection of 14 strip cells. Different grooving methods for cell separation were evaluated regarding the effect on the quality of the groove surface. The effect of the groove passivation, which is regarded as a critical parameter to obtain high-efficiency XIS devices, was simulated to gain a better understanding of the processing requirements

La(Ni,Fe)O3 Stability in the Presence of Cr Species - solid-state Reactivity Study

The solid-state reactivity between La(Ni0.6Fe0.4)O3 (LNF) and Cr2O3 in the IT-SOFC operating temperature range of 600-800 ºC has been investigated using XRD analysis. Because LNF material can be used as a cathode, as a current collecting layer and/or an interconnect coating, a thorough investigation of its chemical stability is of importance for SOFC systems utilizing ferritic stainless steel interconnects. This study demonstrates the intrinsic instability of LNF when exposed to direct contact with Cr2O3 at 800 ºC. It has been observed that Cr enters the perovskite phase, replacing first Ni and then Fe already after 200 h. The rate of the Cr reaction with LNF depends on temperature and exposure time. After 1000 h at 600 ºC no reaction products could be detected with XRD. Although this is a promising result, long-term testing under fuel cell operating conditions is needed to prove LNF as a viable IT-SOFC cathode material

Effects of passivation configuration and emitter surface doping concentration on polarization-type potential-induced degradation in n-type crystalline-silicon photovoltaic modules

System voltages can cause significant degradation in photovoltaic modules. Polarization-type potential-induced degradation (PID) is accompanied by decreases in the short-circuit current density and the open-circuit voltage. The system voltage causes a polarization and surface charge accumulation, increasing the interface recombination. The surface passivation and the emitter doping concentration and gradient are considered to have large impacts. However, a systematic study on these effects has not yet been performed. In this paper, the effects of the front surface structure of n-type passivated emitter and rear totally diffused cell modules were investigated by accelerated PID tests. Standard cells with thin silicon dioxide/80 nm silicon nitride (SiN_x) antireflection/passivation layers, refractive index (RI) of 2.0, exhibited typical polarization-type PID. Cells with increased RI = 2.4 for the bottom 20 nm SiN_x showed no degradation at all. This may be caused by reduced charge accumulation in the SiN_x layer near the interface due to the higher electrical conductivity of the Si-rich bottom layer. Secondly, cells with both a highly distorted interface, due to nitrogen insertion in the silicon surface, and an emitter with a high surface doping concentration have excellent resistance to PID. Cells with either the highly distorted interface or the higher emitter-surface doping concentration show no to minor improved resistance to PID. These findings improve the understanding of the effects of the front surface structure of cells on the polarization-type PID and may contribute to the implementation of these measures to reduce PID

Study of screen printed metallization for polysilicon based passivating contacts

We investigate contacting of n- and p-type polysilicon (polySi) passivating contact layers with industrial screen-printed metal pastes, examining both fire through (FT) and non-fire through (NFT) pastes. The n- and p-type polySi layers, deposited by low pressure chemical vapour deposition and doped by POCl3 diffusion, phosphorus implant, or BBr3 diffusion, result in excellent J(o), even for 50 nm thickness (<2 fA/cm(2) for n-polySi, <10 fA/cm(2) for p-polySi). The contact recombination is investigated by photoluminescence, and by cell test structures to determine V-oc as a function of metallization fraction. The contact resistance is investigated by transfer length method (TLM). The contacts are also extensively studied by high resolution electron microscopy. All-polySi solar cells (i.e., cells with front and back carrier selective layers consisting of polySi) are prepared. Excellent implied V-oc, values of nearly 730 mV and 710 mV are obtained on the un-metallized polished and textured cells, respectively. The contact recombination after applying screen printed metallization can be analyzed well with both methods (PL and V-oc-based) rendering values for the prefactor of the recombination current J(o,c) at the contact areas of about 400 and 350 fA/cm(2) for 200 nm thick n-polySi and p-polySi, respectively. (C) 2017 The Authors. Published by Elsevier Ltd

On the hydrogenation of Poly-Si passivating contacts by Al2O3 and SiNx thin films

Doped polycrystalline silicon (poly-Si), when coupled with a thin SiO2 interlayer, is of large interest for crystalline silicon (c-Si) solar cells due to its outstanding passivating contact properties. To reach high levels of surface passivation, it is pivotal to hydrogenate the poly-Si and the underlying c-Si/SiO2 interface. This can be done by capping the poly-Si with a hydrogen-containing dielectric layer such as Al2O3 or SiNx, followed by a thermal anneal. On the basis of recent research, this work addresses several aspects of such hydrogenation by dielectric materials, including the effect of the annealing ambient, the thermal stability and reversibility of hydrogenation, the poly-Si doping level and c-Si surface texture. Additionally, the implementation of hydrogenation of poly-Si by dielectric materials in solar cells is discussed

Early transition-metal-based binary oxide/nitride for efficient electrocatalytic hydrogen evolution from saline water in different pH environments

Using abundant seawater can reduce reliance on freshwater resources for hydrogen production from electrocatalytic water splitting. However, seawater has detrimental effects on the stability and activity of the hydrogen evolution reaction (HER) electrocatalysts under different pH conditions. In this work, we report the synthesis of binary metallic core-sheath nitride@oxynitride electrocatalysts [Ni(ETM)]δ+-[O-N]δ-, where ETM is an early transition metal V or Cr. Using NiVN on a nickel foam (NF) substrate, we demonstrate an HER overpotential as low as 32 mV at -10 mA cm-2 in saline water (0.6 M NaCl). The results represent an advancement in saline water HER performance of earth-abundant electrocatalysts, especially under near-neutral pH range (i.e., pH 6-8). Doping ETMs in nickel oxynitrides accelerates the typically rate-determining H2O dissociation step for HER and suppresses chloride deactivation of the catalyst in neutral-pH saline water. Heterointerface synergism occurs through H2O adsorption and dissociation at interfacial oxide character, while adsorbed H∗ proceeds via Heyrovsky or Tafel step on the nitride character. This electrocatalyst showed stable performance under a constant current density of -50 mA cm-2 for 50 h followed by additional 50 h at -100 mA cm-2 in a neutral saline electrolyte (1 M PB + 0.6 M NaCl). Contrarily, under the same conditions, Pt/C@NF exhibited significantly low performance after a mere 4 h at -50 mA cm-2. The low Tafel slope of 25 mV dec-1 indicated that the reaction is Tafel limited, unlike commercial Pt/C, which is Heyrovsky limited. We close by discussing general principles concerning surface charge delocalization for the design of HER electrocatalysts in pH saline environments

Study of screen printed metallization for polysilicon based passivating contacts

We investigate contacting of n- and p-type polysilicon (polySi) passivating contact layers with industrial screen-printed metal pastes, examining both fire through (FT) and non-fire through (NFT) pastes. The n- and p-type polySi layers, deposited by low pressure chemical vapour deposition and doped by POCl3 diffusion, phosphorus implant, or BBr3 diffusion, result in excellent Jo, even for 50 nm thickness (<2 fA/cm2 for n-polySi, <10 fA/cm2 for p-polySi). The contact recombination is investigated by photoluminescence, and by cell test structures to determine Voc as a function of metallization fraction. The contact resistance is investigated by transfer length method (TLM). The contacts are also extensively studied by high resolution electron microscopy. All-polySi solar cells (i.e., cells with front and back carrier selective layers consisting of polySi) are prepared. Excellent implied Voc values of nearly 730 mV and 710 mV are obtained on the un-metallized polished and textured cells, respectively. The contact recombination after applying screen printed metallization can be analyzed well with both methods (PL and Voc-based) rendering values for the prefactor of the recombination current Jo,c at the contact areas of about 400 and 350 fA/cm2 for 200 nm thick n-polySi and p-polySi, respectively