Silicon inverted pyramids have been shown to exhibit superior SERS properties compared to ortho-pyramids, yet low-cost, simple preparation processes are lacking at present. This study demonstrates a simple method, silver-assisted chemical etching combined with PVP, to construct silicon inverted pyramids with a uniform size distribution. Two types of Si substrates for surface-enhanced Raman spectroscopy (SERS) were prepared via silver nanoparticles deposited on the silicon inverted pyramids by electroless deposition and radiofrequency sputtering, respectively. The experiments were conducted using rhodamine 6G (R6G), methylene blue (MB) and amoxicillin (AMX) molecules to test the SERS properties of the Si substrates with inverted pyramids. The results indicate that the SERS substrates show high sensitivity to detect the above molecules. In particular, the sensitivity and reproducibility of the SERS substrates with a denser silver nanoparticle distribution, prepared by radiofrequency sputtering, are significantly higher than those of the electroless deposited substrates to detect R6G molecules. This study sheds light on a potential low-cost and stable method for preparing silicon inverted pyramids, which is expected to replace the costly commercial Klarite SERS substrates.

On top of a crystalline silicon wafer, heterojunction solar cells have a thin layer of amorphous silicon (a-Si) placed on it. The efficiency of heterojunction solar cells can be increased by decreasing the electron complex loss by adding an inherent passivation layer to a monocrystalline silicon (c-Si) substrate. In this study, we examine the development of the intrinsic passivation layer deposition technique on c-Si substrates over the previous ten years by several research teams. First, a description of the structure, benefits, and passivation of heterojunction solar cells is given. Following that, the impact of modifying process variables on the functionality of the passivation layer and cell efficiency is explored in terms of the passivation material, hydrogen dilution ratio, substrate temperature, and post-deposition annealing. Last but not least, the ideal process parameters are summed up and potential future research areas are predicted. One of the best ways to increase the conversion efficiency of heterojunction solar cells is through surface passivation technology, and future domestic and international research will focus heavily on the process technology of its intrinsic passivation layer.

Silicon heterojunction (SHJ) solar cells are increasingly attracting attention due to their low-temperature processing, lean steps, significant temperature coefficient, and their high bifacial capability. The high efficiency and thin wafer nature of SHJ solar cells make them ideal for use as high-efficiency solar cells. However, the complicated nature of the passivation layer and prior cleaning render a well-passivated surface difficult to achieve. In this study, developments and the classification of surface defect removal and passivation technologies are explored. Further, surface cleaning and passivation technologies of high-efficiency SHJ solar cells within the last five years are reviewed and summarized.

In this work, we present a breakthrough in boronsilicate glass (BSG) passivated industrial tunnel oxide passivated contact (i-TOPCon) solar cells. We find that a high-temperature firing process significantly improves the front side BSG passivation quality; however, the use of such high-temperatures is undesirable for metallization as it could lead to more junction damage by the metal paste spikes. In this study, we present a simple and industrially viable method to resolve this dilemma. With a high-temperature industrial firing activation step to maximize the potential of BSG passivation, a low emitter saturation current (J(0e)) of 34 fA/cm(2) has been achieved, demonstrating excellent boron emitter passivation that is comparable to state-of-the-art SiO2 and Al2O3-based passivation methods on similar structures and boron emitters. Applying this solution to cell device, the open-circuit voltage (V-oc) is improved by about 6 mV, corresponding to an absolute cell efficiency improvement of about 0.2%. Furthermore, after activating the BSG passivation, a lower temperature paste could be used at the rear side which further improves the V-oc by around 3 mV. Combined together, an overall improvement of V-oc close to 10 mV is achieved, propelling the cell V-oc into the 690-mV era. The effectiveness of this solution was also verified in a mass production line, with average cell efficiencies of around 23.2% (0.5% more than the baseline) and a maximum cell efficiency and V-oc of 23.4% and 693 mV, respectively. This work opens new routes for further improving conventional solar cell efficiencies, in particular for BSG-passivated TOPCon solar cells.

This work investigates the interface properties of intrinsic hydrogenated amorphous silicon film passivated wafers that underwent hydrogen plasma cleaning. A high level of interface band bending of nearly −0.6 eV, which corresponds to a fixed charge of −2.2 × 10 12 cm −2 , is found to be responsible for an effective minority carrier lifetime of over 6 ms on the 4.5 Ω cm n‐type wafer, while such field‐effect passivation is missing in hydrofluoric acid (HF) cleaned wafers. Further study indicates a positive correlation between the extent of surface band bending and doping concentration, together with an inverted U‐shape with respect to the increased annealing condition. The fixed charge on p‐type wafer is found to have a higher “formation energy” compared with the n‐type case, which renders its field‐effect passivation much less effective due to H effusion at high annealing temperatures. With reference to the theory on donor/acceptor‐H complex upon H plasma treatment, the origin and observed properties of the surface band bending on both dopant types are discussed. The unique presence of field effect on hydrogen plasma cleaned n‐type wafers can provide new insights into passivation material selection and structural design of heterojunction silicon wafer solar cells.

In this work, we use ultra-thin thickness-controllable spatial atomic layer deposited (ALD) aluminium oxide (AlOx) tunnel layers, which contain high negative fixed charges (Q(f)), capped by highly boron-doped polysilicon layers to form tunnel layer passivated contacts. The high Qf of the tunnel layers is expected to enhance the carrier selectivity of these passivated hole-extracting contacts. The dependence of the ALD AlOx tunnel layer contact passivation performance on its thickness is investigated. Furthermore, two different thermal charge activation conditions, i.e., fast firing using a belt furnace at 700 and 800 degrees C are compared. The best measured recombination current density J(0) and implied open-circuit voltage iV(oc) of the developed AlOx/polysilicon passivated contacts with a symmetrical AlOx/SiNx stack passivation are 6.6 fA/cm(2) and 723 mV, respectively. Based on the measured J(0) and on the measured total contact resistivity of the passivated contact, the practical efficiency limit of a rear-side full area passivated contact solar cell with a conventionally diffused front side is calculated to be as high as 23.2%. Additionally, three rear-side metallization schemes: (1) thermally evaporated full-area silver contacts; (2) screen-printed non-firing-through aluminium contacts and (3) screen-printed firing through silver-aluminium contacts, are compared. Finally, rear-emitter solar cells, using a rear-side hole-selective AlOx tunnel layer passivated contact, are fabricated, which shows an efficiency of up to 20.5%. While the proposed hole-selective passivated contact scheme appears to be promising based on the simulation prediction, the efficiency of the fabricated cells is largely limited by the non-optimized front-side reflectance and recombination losses as well as the use of non-optimized rear-side metallization schemes.

In this work, we explore the feasibility to deposit silicon oxide passivating thin films using a fully atmospheric pressure plasma coater to replace vacuum based processes such as plasma-enhanced chemical vapor deposition (PECVD). It is demonstrated that by using suitable precursors and plasma settings, the deposited film thickness can be accurately controlled for application in high-efficiency solar cell structures. The deposited film is confirmed to be SiO2 close to its stoichiometric structure. By depositing the film onto industrial n-type Czochralski (Cz) Si wafers, effective lifetimes of up to 500 mu s are achieved which demonstrates the potential of the atmospheric pressure plasma-deposited passivation film.

Substituting silver screen printing with copper plating for silicon wafer solar cell metallisation can significantly lower the material costs associated with cell production. However, given the recent improvements in screen printing (robust fine-line printing screens and improved paste formulations), plating processes also need to be rapidly advanced to remain a viable alternative to screen printing. In this paper, we describe novel processes enabling improved plating for silicon wafer solar cells. Specifically, we investigate two such processes: 1) the use of femtosecond (fs) laser pulses for dielectric ablation for plated contacts and 2) the use of an ambient plasma surface treatment as an adhesion promoting pretreatment for plating directly on the indium tin oxide (ITO) layer in silicon heterojunction cells.

Measurement of infrared (IR) reflectance and transmittance are proven methods for rapid inline process monitoring of doped layers formation. This work presents two experiments where multiple layer properties can be simultaneously determined using appropriate IR measurements: 1) separation of the sheet resistances of front and rear diffused layers, derived from IR front incident reflectance and transmittance data, and; 2) resolution of the sheet conductance and thickness of front and rear ITO layers, derived from IR front incident reflectance, transmittance and rear incident reflectance data. Both of these scenarios are further articulated using ray tracing modelling combined with sensitivity analysis. Finally, this type of simulation is also used to predict the ability of the IR interactions to resolve phosphorus diffused layer surface concentration independently of the sheet resistance. The simulation shows that reliable resolution is achievable, as long as the surface active dopant concentration exceeds 2 x 10(19) cm(-3).

Hydrogenated doped silicon thin films deposited using Inductively Coupled Plasma Enhanced Chemical Vapour Deposition were investigated for their film characteristics. In particular, the dilution ratio (H 2 : SiH 4 ) and trimethylborane dopant gas ratio (TMB: SiH 4 ) were varied in order to analyze their effect on the degree of crystallinity and conductivity. μRaman Spectroscopy and 4-Point Probe techniques were employed to investigate the transverse optical peaks of the three silicon phases and obtain 9-point conductivity mapping of the full-area film, respectively. Effective minority carrier lifetimes and implied opencircuit voltages were analyzed via Quasi-Steady State Photoconductance method. High-quality a-Si:H(p)/a-Si:H(i)/cSi(n)/a-Si:H(i)/a-Si:H(n) stacks capped with transparent conductive oxide on both sides were fabricated with an implied open-circuit voltage around 760 mV.

In our previous work, we demonstrated that minority carrier lifetime can be improved after an atmospheric pressure plasma treatment on amorphous silicon suboxide passivated silicon surface [1]. In this work, we explore the feasibility to deposit silicon oxide passivation thin films using a fully atmospheric pressure plasma coater to replace vacuum based processes such as PECVD. The experiment was carried out using a Plasma Plus System (Plasmatreat, Germany). Silicon wafers that underwent a standard cleaning procedure were dipped in hydrofluoric (HF) acid for chemical oxide removal. An evaporator that can operate at different temperatures was used to vaporize the liquid precursor hexamethyldisiloxane (HMDSO) before it was charged into the plasma jet using nitrogen (N2) as a carrier gas. The plasma species after glow-discharge were dispensed onto the wafer surface to form the passivation film. The film properties were adjusted using various deposition parameters: HMDSO flow rate, evaporator temperature, distance between plasma nozzle head and the surface, and the speed of the nozzle head travelling across the wafer. The thickness of the film was determined by both spectroscopic ellipsometry and transmission electron microscope, while the passivation quality was measured using quasi-steady-state photoconductance decay method. It was found that using the atmospheric pressure plasma coater, symmetrical passivation can be realized in less than 50 s with good uniformity. The lowest controllable oxide thickness was around 5 nm, which represents a promising application in heterojunction solar cell fabrication. By using device relevant oxide thickness, good minority carrier lifetime can be achieved. Comparing with passivation samples prepared by vacuum process, the atmospheric pressure plasma coater can achieve similar level of passivation with better uniformity in a shorter time and a much lower cost. However, it was discovered that the resulting oxide properties are highly sensitive to the abovementioned parameters. In particular, the evaporator temperature determines the carbon content in the film, which in turn affects the passivation quality and surface contaminant concentration. The precursor flow rate, together with the nozzle head travelling speed determines the growth rate and the film density. Currently, good passivation quality at device relevant thickness can only be achieved on a fairly small process window.

In this work, we demonstrate an alternative technique to develop high-quality p-doped hydrogenated amorphous silicon [a-Si:H(p)] thin film layers for heterojunction applications over the more commonly employed direct capacitatively coupled plasma (CCP) deposition method [1,2]. a-Si:H(p) thin layers were fabricated using inductively coupled plasma enhanced chemical vapour deposition (ICPECVD) technology via an industrial-scale platform, the SINGULAR-HET. Through delicate optimisation of key parameters, aSi:H(p) layers were successfully deposited on n-type Cz wafers and borosilicate glass for conductivity, micro-Raman spectroscopy and spectroscopic ellipsometry (SE) analysis. In particular, the conductivity of the layer is highly dependent on the dilution ratio (H2: SiH4) R, of the gas mixture. A peak conductivity of 1.48 Scm was achieved with R more than 5 (Figure 1). It is predicted that too low a dilution ratio reduces the degree of crystallinity of the p-layer (Figure 2), while dilution ratios that are too high reduce the film thickness.

In this work, the effect of an ambient plasma treatment powered by compressed dry air on the passivation quality of silicon wafers coated with intrinsic amorphous silicon sub-oxide is investigated. While long-time storage deteriorates the effective lifetime of all samples, a short ambient plasma treatment improves their passivation qualities. By studying the influence of the plasma treatment parameters on the passivation layers, an optimized process condition was identified which even boosted the passivation quality beyond its original value obtained immediately after deposition. On the other hand, the absence of stringent requirement on gas precursors, vacuum condition and longtime processing makes the ambient plasma treatment an excellent candidate to replace conventional thermal annealing in industrial heterojunction solar cell production. (C) 2017 The Japan Society of Applied Physics

Hydrogenated intrinsic amorphous silicon suboxide thin films deposited onto c-Si wafers by decomposing hydrogen, silane, and carbon dioxide in an industrial remote inductively coupled plasma tool are studied. Compared with intrinsic amorphous silicon deposited in the same tool, this material displays an improved process temperature window and excellent surface passivation quality, which is important for industrialization. The wide process window of over 200 °C (100 to 350 °C) mainly results from the slow depletion of H atoms at elevated temperature due to a suppressed epitaxial growth, whereas the excellent passivation quality is due to a much higher H content in the film compared with amorphous silicon. The temperature stability is further supported by a study using a high-resolution transmission electron microscopy. Under the optimal condition, the amorphous silicon suboxide demonstrates an effective minority carrier lifetime of over 4.7 ms on planar n-type 1-Ω · cm Czochralski silicon wafers, which is equivalent to an effective surface recombination velocity of less than 1.7 cm/s, and an implied open-circuit voltage of 741 mV.

A hydrofluoric-acid (HF)-free hydrogen plasma dry etching process prior to the deposition of intrinsic amorphous silicon onto thin n-type planar Czochralski silicon wafers is developed. The influence of substrate temperature, hydrogen flow rate, and power density on the passivation quality is investigated. Advanced characterization using spectroscopic ellipsometry and transmission electron microscopy shows the impact of the etching conditions, especially the temperature and gas flow rates, on the surface quality and interface properties. It is found that the native oxide can only be removed effectively when wafers are subjected to higher temperature or lower hydrogen flow rate. The hydrogen, oxygen, and carbon concentration profiles at the a-Si/c-Si interface of the plasma-etched samples are studied and compared with the traditionally HF cleaned interface to gain a better understanding of the reasons for the superior passivation quality.

In this work, hydrogen plasma etching of surface oxides was successfully accomplished on thin (approximate to 100 mu m) planar n-type Czochralski silicon wafers prior to intrinsic hydrogenated amorphous silicon [a-Si:H(i)] deposition for heterojunction solar cells, using an industrial inductively coupled plasma-enhanced chemical vapour deposition (ICPECVD) platform. The plasma etching process is intended as a dry alternative to the conventional wet-chemical hydrofluoric acid (HF) dip for solar cell processing. After symmetrical deposition of an a-Si:H(i) passivation layer, high effective carrier lifetimes of up to 3.7 ms are obtained, which are equivalent to effective surface recombination velocities of 1.3 cm s(-1) and an implied open-circuit voltage (V-oc) of 741 mV. The passivation quality is excellent and comparable to other high quality a-Si:H(i) passivation. High-resolution transmission electron microscopy shows evidence of plasma-silicon interactions and a sub-nanometre interfacial layer. Using electron energy-loss spectroscopy, this layer is further investigated and confirmed to be hydrogenated suboxide layers. ((c) 2015 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Excellent carrier lifetime is obtained by applying a rapid low-temperature hydrogen plasma etch before the deposition of intrinsic amorphous silicon in an industrial ICPECVD reactor. The hydrogen etch process substitutes a conventional HF dip and removes surface oxides via the rapid hydrogen plasma. Process development details such as influence of the temperature, flow rate and power density on the lifetime are presented. Interface comparison is carried out on plasma etched and HF dipped samples by using transmission electron microscopy, electron energy loss spectroscopy and time-of-flight secondary ion mass spectroscopy. It is found that the interface is both hydrogen and oxygen rich compared to HF-etched reference samples. Epitaxial growth is suppressed. Using amorphous silicon suboxide for subsequent surface passivation, the plasma etched samples show excellent lifetimes of 6.1 ms on a 6 inch 1 Ωcm n-type wafer. This hydrogen plasma etch process may be an excellent alternative to conventional HF treatment for heterojunction silicon solar cell fabrication.

One of the most promising advanced solar cell designs for <; 100 μm thin silicon wafers is the heteroj unction silicon wafer solar cell (HET), with a very high efficiency potential with cost-effective low-temperature processing. In collaboration with German company Singulus Technologies and other industrial collaborators, SERIS is developing a pilot line suitable for mass production of HET cells. Initial experiments on the inductively coupled plasma deposition of a-Si:H(i) and compositionally similar alloy films such as a-SiOx:H(i) have yielded very good results compatible with high-voltage HET solar cells, with the passivation quality of a-SiOx:H(i) being consistently higher, and far less sensitive to the deposition temperature compared to a-Si:H(i). In fact, a-SiOx:H(i) has a stable process window of more than 200°C that is suitable for the production environment. The wider process window can be attributed to suppressed epitaxial growth and incubation layer thickness in the a-SiOx:H(i) layer at high deposition temperatures.

We present an alternative method of depositing a high-quality passivation film for heterojunction silicon wafer solar cells, in this paper. The deposition of hydrogenated intrinsic amorphous silicon suboxide is accomplished by decomposing hydrogen, silane, and carbon dioxide in an industrial remote inductively coupled plasma platform. Through the investigation on CO2partial pressure and process temperature, excellent surface passivation quality and optical properties are achieved. It is found that the hydrogen content in the film is much higher than what is commonly reported in intrinsic amorphous silicon due to oxygen incorporation. The observed slow depletion of hydrogen with increasing temperature greatly enhances its process window as well. The effective lifetime of symmetrically passivated samples under the optimal condition exceeds 4.7 ms on planarn-type Czochralski silicon wafers with a resistivity of 1 Ωcm, which is equivalent to an effective surface recombination velocity of less than 1.7 cms−1and an implied open-circuit voltage (Voc) of 741 mV. A comparison with several high quality passivation schemes for solar cells reveals that the developed inductively coupled plasma deposited films show excellent passivation quality. The excellent optical property and resistance to degradation make it an excellent substitute for industrial heterojunction silicon solar cell production.