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An alternative catalytic method was employed using the reduction of Pd ions on the surface of cetyltrimethylammonium bromide (CTAB) treated laponite to initiate the electroless plating of copper; the deposition features of the Pd nanoparticles produced were investigated in detail. Results indicated intercalation and reduction of Pd nanoparticles occurred at room temperature and involved interaction between the laponite and the cetyltrimethylammonium cationic templates. Organic species and amount on laponite were optimized to adjust silicate platelet interlayer distances and platelet organophilic properties. Intercalation of Pd nanoparticles occurred between the magnesium silicate layers of laponite and this was dependent on pre-treatment and impregnation times. As impregnation is a method of producing heterogeneous catalysts, we considered Pd nanoparticles on laponite templates could catalyze the electroless deposition of Cu to initiate metallization. Cu films fabricated on laponite templates exhibited excellent surface roughness (˜1.7 nm) and low resistivity (˜3.42 μΩ). The devised approach enabled the facile formation of a network suitable for Cu metallization without causing substrate damage and produced metal surfaces with excellent flatness and resistivity.

Boron-diffused samples passivated by Al2O3/TiO2 stacks with different types of TiO2 were investigated. An emitter saturation current density of 11 × 10−15 A/cm2 was obtained for Al2O3/TiO2 passivated samples with symmetrical 100 Ω/sq. boron diffusion. The surface passivation of Al2O3/TiO2 stacks was strongly impacted by the temperature, gas, and sequence during two-step annealing. In addition, the saturation current density of the Al2O3/TiO2 stacks is influenced by the TiO2 layers with an O3 treatment. Enhanced passivation performance of the Al2O3/TiO2 stacks was achieved by a combination of appropriate TiO2 capping layer and post-annealing. The results of this study provide reliable criteria for the design of thermally-stable Al2O3/TiO2 stacks on high-efficiency silicon solar cells.

The characteristics of laser ablation prepared on the structures of a passivated emitter and rear cell (PERC) using additional laser irradiation were investigated. Particular emphasis was placed on the distribution of laser damage and contact geometry on the cell performance. The residual Al2O3 passivation layer of the Al2O3/SiNx passivated samples was removed almost completely by three laser shots. No severe damage profile was observed near the silicon surface, but damage profiles with a thickness of 10–15 nm were observed in the form of amorphous silicon. Additional laser irradiation after contact opening generally degraded the passivation quality with increasing laser shots, and the depth of laser-induced damage was a few micrometers. Interestingly, the PERC cells fabricated using three laser shots had higher efficiency than that produced by one laser shot. This was attributed to the chemical reaction between the silicon and Al paste, resulting in a eutectic alloy and back surface field, which was much thicker than the depth of laser damage. Consequently, the laser damage by the ablation process can be recovered by metallization during the fabrication of PERC cells. The experimental analyses highlighted that the fraction of point contact is a fundamental parameter in the design of PERC cells. The reduction of fraction of point contacts to reduce the recombination losses at rear surface led to an increase of series resistance. Therefore it is necessary to optimize the width and pitch of point contacts for high-efficiency solar cells.

N-type phosphorus diffusion in silicon using phosphorus oxychloride, POCl3, has been widely used in the production of p-type silicon solar cells. The thermal diffusion process in a furnace generally involves two steps: pre-deposition and drive-in. The phosphorous doping by thermal diffusion often shows high surface concentrations, leading to an increase in charge recombination, which should be inhibited in order to fabricate high efficiency silicon solar cells. In this study, we investigate the influence of 3 drive-in steps at sequentially increasing temperatures during the POCl3 diffusion on the emitter performance. As a result, it was found that the kink region was made shorter while maintaining surface concentration for a good metal contact without losing its passivation quality. This result is attributed to the higher active dopant concentration of the 3 drive-in step samples, leading to a lower series resistance and higher fill factor in the PERC solar cells. The results show that slight changes in the PSG process conditions can contribute to the improvement of high efficiency solar cells.

Al2O3/TiO2 stacks formed by atomic layer deposition are known to provide a high level of passivation for boron-doped silicon. In previous works, the TiO2 layer was deposited on a pre-annealed Al2O3 layer, however this stack showed passivation degradation after post-deposition annealing. This work presents an alternative to using the as-deposited Al2O3 for the Al2O3/TiO2 stack, which shows no degradation of passivation after post-deposition annealing up to 400 °C. This approach simplifies the processing, allowing continuous layer deposition, and eliminates the undesirable vacuum breaking. This simplified processing leads to better thermal stability of the Al2O3/TiO2 stacks and a low emitter saturation current density. In order to understand the underlying mechanism of surface passivation, an investigation on the effect of thermal SiO2 on the passivation of the Al2O3/TiO2 stack was performed, which indicates that the TiO2 capping layer enhances the field-effect passivation for both the Si/Al2O3 and SiO2/Al2O3 structures.

Gapless interdigitated back contact (IBC) solar cells were fabricated with phosphorous back surface field on a boron emitter, using an ion implantation process. Boron emitter (boron ion implantation) is counter doped by the phosphorus back surface field (BSF) (phosphorus ion implantation) without gap. The gapless process step between the emitter and BSF was compared to existing IBC solar cell with gaps between emitters and BSFs obtained using diffusion processes. We optimized the doping process in the phosphorous BSF and boron emitter region, and the implied Voc and contact resistance relationship of the phosphorous and boron implantation dose in the counter doped region was analyzed. We confirmed the shunt resistance of the gapless IBC solar cells and the possibility of shunt behavior in gapless IBC solar cells. The highly doped counter doped BSF led to a controlled junction breakdown at high reverse bias voltages of around 7.5 V. After the doping region was optimized with the counter doped BSF and emitter, a large-area (5 inch pseudo square) gapless IBC solar cell with a power conversion efficiency of 22.9% was made.

Copper has unique properties, such as low electrical resistivity, that are exploited in a number of applications, including an interconnect layer in integrated circuits and microelectronic devices. Etching techniques are essential for the fabrication of fine structures, devices, and circuits. This article addresses the methods of copper etching with an emphasis on approaches using ferric nitrate. Potentiodynamic polarization tests using benzotriazole as an inhibitor showed that ferric nitrate has higher inhibition efficiency than conventional etchants. This is because benzotriazole in a ferric nitrate solution is adsorbed on the copper surface to a greater extent than in a ferric chloride and cupric chloride solution, as confirmed by Fourier transform infrared analysis. Quantitative atomic force microscopy characterization showed that good surface quality with significantly lower surface roughness can be obtained from a copper film etched in a ferric nitrate solution, which has potential use in microelectronics manufacturing.

Silicon solar cells passivated with Al2O3 require a capping layer that protects the passivation layer from humidity because of sensitivity of Al2O3 to moisture. Al2O3/TiO2 stacks obtained by atomic layer deposition have been known to provide a high level of passivation layers because of their excellent field-effect passivation. In this work, degradation of this Al2O3/TiO2 stack, when exposed to humidity, is examined, and an attempt is made for a humidity-resistant encapsulation layer by adding Al2O3/TiO2 nanolaminates that can be deposited in-situ without breaking vacuum. Placing the nanolaminate on top of the TiO2 and Al2O3 stack is found to lead to almost no degradation even after 10 days of humidity exposure. (© 2015 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

We investigate the effect of O3 and H2O oxidant pre-pulse prior to Al2O3 atomic layer deposition for Si surface passivation. Interfacial oxide SiOx formed by the O3 pre-pulse is more beneficial than that by H2O to a high level of surface passivation. The passivation of thinner H2O–Al2O3 films is more improved by this O3 pre-pulse. O3 pre-pulse for 10 nm H2O–Al2O3 reduces saturation current density in boron emitter to 18 fA cm–2 by a factor of 1.7. Capacitance–voltage measurements reveal this interfacial oxide plays a role of decreasing interface trap density without detrimental effect to negative charge density of Al2O3. (© 2014 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Chemical processes are very important for the development of high-efficiency crystalline solar cells, mainly for surface texturing to improve light absorption and cleaning processes to reduce surface recombination. Recently, research has been focusing on the impact of chemical polishing on the performance of a passivated emitter and rear cells (PERC), with particular emphasis on the dielectric passivation layers on the front side. This study examined the influence of etching on the passivation of Al2O3/TiO2 stacks, where the films may each be deposited using a range of deposition and post-annealing parameters. Most TiO2 films deposited at 300 &deg, C were resistant to chemical etching, and higher temperature deposition and annealing produced more chemical-resistant films. TiO2 films deposited at 100 &deg, C were etched slightly by SC1 and SC2 solutions at room temperature, whereas they were etched at a relatively high rate in an HF solution, even when capped with a thick TiO2 layer (up to 50 nm in thickness), blistering occurred in 20-nm-thick Al2O3 films. In contrast to the as-deposited films, the annealed films showed a lower level of passivation as 1% HF etching proceeded. The implied open circuit voltage of the samples annealed at 300 &deg, C after HF etching decreased more than those annealed at 400 &deg, C. The dark area in the photoluminescence images was not resistant to the HF solution and showed more etch pits. The etching strategies developed in this study are expected to help setup integration processes and increase the applicability of this stack to solar cells.

In this work atomic layer deposition of Al2O3 and TiO2 has been used to obtain dielectric stacks for passivation of silicon surfaces. Our experiments on n- and p-type silicon wafers deposited by thin Al2O3/TiO2 stacks show that a considerably improved passivation is obtained compared to the Al2O3 single layer. For Al2O3 films thinner than 20 nm the emitter saturation current density decreases with increasing TiO2 thickness. Especially the passivation of ultrathin (∼5 nm) Al2O3 is very effectively enhanced by TiO2 due to a decreased interface defect density as well as an increased fixed negative charge in the stacks. Hence, the thin Al2O3/TiO2 stacks developed in this work can be used as a passivation coating for Si-based solar cells. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Boron-diffused p+/n/p+ and undiffused silicon samples with (1 0 0) and (1 1 1) orientations passivated by aluminum oxide (Al2O3) that is synthesized by atomic layer deposition (ALD) have been investigated. Emitter saturation current densities of ~24, 29, and 33 fA/cm2 were obtained for (1 0 0) samples with symmetrical 85Ω/□ B diffusions that were passivated by plasma-assisted, H2O-based, and O3-based ALD Al2O3, respectively. Compared with undiffused samples, it was found that the additional surface doping from the diffusion reduces recombination at the Al2O3/Si interface in the case of relatively low surface boron concentrations (

Passivated emitter and rear contact (PERC) is a promising technology owing to high efficiency can be achieved with p-type wafer and their easily applicable to existing lines. In case of using p-type mono wafer, 0.5–1% efficiency increase is expected with PERC technologies compared to existing Al BSF solar cells, while for multi-wafer solar cells it is 0.5–0.8%. We addressed the optimization of PERC solar cells using the Al paste. The paste was prepared from the aluminum–silicon alloy with eutectic composition to avoid the formation of voids that degrade the open-circuit voltage. The glass frit of the paste was changed to improve adhesion. Scanning electron microscopy revealed voids and local back surface field between the aluminum electrode and silicon base. We confirmed the conditions on the SiNx passivation layer for achieving higher efficiency and better adhesion for long-term stability. The cell characteristics were compared across cells containing different pastes. PERC solar cells with the Al/Si eutectic paste exhibited the efficiency of 19.6%.

A detailed study of the passivation quality of Al2O3 and TiO2 stacks on boron-doped emitters, where the stacks were deposited by thermal atomic layer deposition. The passivation quality was studied for different post-TiO2 anneal temperature, as a function of Al2O3 and TiO2 layer thickness. For annealed Al2O3 layers, as-deposited TiO2 capping layer decreased emitter saturation current density considerably, which was more significant on Al2O3 with thickness below 10 nm. However, post-TiO2 deposition anneal in O2 environment degraded the passivation, which was attributed to the increasing interface trap density in spite of increasing effective fixed charge density.

The effect of humidity on boron diffused and undiffused silicon samples passivated by aluminum oxide (Al 2 O 3 ) synthesized by plasma-assisted atomic layer deposition (PA-ALD) has been investigated. We found that undiffused samples show a higher degradation rate than diffused samples. Under an ambient of 100% relative humidity and 50°C, the lifetime of an undiffused sample passivated by Al 2 O 3 decreased from 1500 to 400μs after 28 hours of exposure, whereas the saturation current density of the diffused region J op+ of a boron diffused sample was nearly unchanged after 7 days of exposure. As expected, for both diffused and undiffused samples, the degradation rate is accelerated by increasing the temperature of the humidity environment. A PECVD SiN x , capping layer acts as an effective protection layer for Al 2 O 3 to resist a damp-heat conditions of 100% relatively humidity at 80°C. The electrical resistance of PA-ALD Al 2 O 3 was observed to degrade in humidity. Fourier Transform Infra-red Spectroscopy (FTIR) measurements indicate that damp heat results in a structural modification of the bulk Al 2 O 3 film and the formation of AlO(OH). This change could be responsible for the fast degradation rate of PA-ALD Al 2 O 3 passivation compared with SiO 2 . Finally, we experimentally demonstrated that the degraded passivation of an Al 2 O 3 layer can be repaired by light illumination and negative corona charge deposition.

This project has been supported by the Australian Government through the Australian Solar Institute, part of the Clean Energy Initiative.