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Different passivation layers on phosphorous diffused emitters have been studied. A comparison between silicon nitride (SiN x ) single layer at different deposition temperatures, stacks of ""outgassing"" silicon oxide (that was grown during the moving in/out of the furnace in ambient air during the outgassing process) and an ultrathin SiO x layer formed by plasma oxidation capped with SiN x layers have been investigated. Optimization of plasma enhanced chemical vapor deposition (PECVD) SiNx at different deposition temperatures showed good passivation quality depending on the hydrogen content. Plasma oxidation process by a PECVD tool without utilizing a silicon source in the process gas flow is an obvious choice to form a thin SiOx as it allows the formation of a SiO x /SiN x stack in a sequence of deposition processes in the same inline PECVD tool. Such an ultrathin SiO x layer was found to not only improve the surface passivation after a fast firing process but also to maintain the excellent anti-reflection coating (ARC) property of the SiN x . Low emitter saturation current density J oe values of 15 fA/cm 2 for planar and 24 fA/cm 2 for textured surfaces for an emitter with a sheet resistivity of 161 O/ sq has been reached after firing at 850 °C, which is comparable with the outgassing oxide. These stacks gave an improvement of the J oe values with a factor of 6-9 for emitters with low surface concentration comparing to single SiN x layer.

In this paper, one-dimensional analytical model is presented that reproduces lateral changes in p-n junction voltage as a result of recombination at line defects. The model takes into account the majority charge carrier transport in the emitter and in the base over a long distance (>1 mm) as induced by a line defect (for example, a metal finger, an edge, or any line-shaped region with a higher recombination rate). The model predicts the p-n junction voltage as a function of distance to the recombination center in one dimension. The model is compared with numerical device simulations using Quokka3 for two scenarios typical in current state-of-the-art solar cells. The deviation of the lateral p-n junction voltage is less than 1 mV for contact recombination and less than 4 mV for edge recombination. These results show that over the relevant distances, the carrier transport is almost purely resistive, validating the main hypothesis of this model. Such good agreement, and the corresponding compatibility with numerical device simulations, renders the model a useful tool for the interpretation of experimental results.

This work demonstrates the efficient optical and passivation properties provided by hydrogenated silicon nitride (SiNx:H) layers deposited in a lab‐scale atmospheric pressure plasma enhanced chemical vapor deposition (AP‐PECVD) reactor. By applying modulated low‐frequency plasma (200 kHz), homogeneous SiNx:H layers, with small variances in thickness w and refractive index n (Dw < 2 nm; Dn < 0.02), were achieved on a surface area of 45 × 55 mm2. The use of voltage amplitude modulation enabled discharge optimization and led to greatly enhanced SiNx:H film homogeneity and conformity in comparison with continuous plasma discharge conditions. Additionally, AP‐PECVD SiNx:H showed good thermal stability (Dw < 1 nm; Dn < −0.02) with low absorption coefficients (k < 0.1 at 275 nm), demonstrating that such layers could act as efficient antireflective coatings. Furthermore, outstanding surface passivation properties were achieved after firing, both on n‐type FZ c‐Si substrates of standard 2.8 O.cm doping (teff = 1.45 ms) and on highly doped 85 O/sq n+ emitters (j0e = 74 ± 2 fA.cm−2). Finally, AP‐PECVD SiNx:H thin films were tested on industrial passivated emitter and rear solar cell (PERC) architectures, where the potential of applying these layers both as efficient rear‐side capping layer and front‐side antireflective coating was demonstrated. The first lab‐scale 40 × 40 mm2 PERC solar cells featuring AP‐PECVD SiNx:H layers led to conversion efficiencies of up to 20.6%. These results pave the way for upscaling the dielectric barrier discharge lab‐scale reactor in an industrial in‐line process, which could provide low‐cost and high‐throughput SiNx:H capping and antireflective layers.

The extraction of the implied open-circuit voltage ( iV OC ) and saturation current density under the metal fingers ( j 0met ) using a single photoluminescence (PL) image is demonstrated in this article. The method employed to derive these parameters is based on an analytical modeling of the local p-n-junction voltage between the metallization fingers and on the analysis of the p-n-junction voltage variations obtained using a calibrated PL image. The image is analyzed in the Fourier space; taking advantage of the periodicity of the metal grid, the relevant information is extracted from the first two Fourier peaks. The ( iV OC ) and ( j 0met ) are calculated from the peaks intensities. This method is compared with one that uses two PL images. Both methods agree within their uncertainty ( ± 200 fA/cm² for j 0met ). The main advantage of the method developed in this article is that only one image is required.

This article introduces a postmetallization ""passivated edge technology"" (PET) treatment for separated silicon solar cells consisting of aluminum oxide deposition with subsequent annealing. We present our work on bifacial shingle solar cells that are based on the passivated emitter and rear cell concept. To separate the shingle devices after metallization and firing, we use either a conventional laser scribing mechanical cleaving (LSMC) process or a thermal laser separation (TLS) process. Both separation processes show similar pseudo fill factor (pFF) drops of − 1.2% abs from the host wafer to the separated state. The pFF of the TLS-separated cells increases by up to +0.7% abs from the as-separated state after PET treatment due to edge passivation, while the pFF of LSMC-separated cells increases by up to +0.3% abs . On cell level, the combination of TLS and PET allows for a designated area output power density of p out = 23.5 mW/cm², taking into account an additional 10% rear side irradiance.

This work aims to improve the rear-side properties of p -type monocrystalline silicon solar cells by using the passivated emitter and rear locally diffused (PERL) solar cell concept. To realize the rear side structure, the so-called PassDop approach was used combining both surface passivation and local doping. The concept utilizes a multifunctional, doped AlO x /SiN x :B layer stack; the localized structuring is achieved by local contact opening and doping by a laser process. Using AlO x /SiN x :B PassDop layers, an outstanding effective surface recombination velocity S eff of less than 4 cm/s was achieved after firing at the passivated area. The boron concentration in the PassDop layers did not show any significant influence on S eff . Laser doping resulted in highly doped regions in the silicon with a sheet resistance of below 20 Ω/sq and surface doping concentrations close to 1 × 1020 cm–3. Accordingly, calculations showed that the saturation current density at the laser doped areas can be as low as 900 fA/cm² for line-shaped contact structures.

In this contribution, atmospheric pressure dry etching (ADE) texture is integrated into a passivated emitter and rear cell (PERC) process. In order to make the texture suitable for the solar cell processing, two post-etching processes (inverted pyramid, spherical cap) are implemented and compared. The passivation of the front surface could be improved substantially by the introduction of an Al 2 O 3 layer deposited via atomic layer deposition under the classical antireflection coating SiN X . The impact of the addition of the Al 2 O 3 layer on the contact resistance cannot be neglected and becomes significant for thicknesses higher than 4 nm. Multicrystalline silicon (mc-Si) PERC solar cells are fabricated and measured, leading to a maximum efficiency of about 18.6% for the acidic texture, and for both posts-processed dry chemical etching (ADE) textures. No current gain for the ADE textured wafer compared to the acidic texture could be observed on cell level due to an inhomogeneous etching. However, a gain of 0.4 mA/cm 2 for the ADE texture was calculated from local EQE measurements. ADE texture presents therefore 2 advantages: compatibility to diamond wire sawing and a potential current gain for PERC solar cell structure.

We present different models for the internal resistance of passivated emitter and rear totally diffused (PERT) solar cells. First we apply the model of Gelmont and Shur for the spreading resistance of a passivated emitter and rear cell (PERC) structure with line-shaped contacts and adapt this model to account for the elliptic contact shape of Al-alloyed contacts. To account for the additional vertical current flow through the silicon wafer and the lateral current flow through the back surface field (BSF) of a PERT structure, we evaluate an alternative model using the analogy to the transfer length method (TLM) problem. For experimental verification, we have fabricated resistance test structures for various wafer resistivities, BSF doping levels and line distances (finger pitches) of the line-shaped contacts. Our experimental data shows good agreement with the presented models in distinct parameter ranges and thus offers a solid basis for analytical modelling of PERT-type solar cells.

In this paper, we study the impact of change in emitter diffusion profiles on the electrical characteristics of nanotextured surfaces formed by an inline plasma-less dry-chemical etching process. Our experimental results and process simulations suggest that a deeper highly doped region and a significantly higher inactive P concentration in the emitter plays a determining role in defining recombination, as well as the resistive losses in nanotextured surfaces. Low emitter saturation current densities on phosphorous-diffused surfaces are achievable after passivation with either SiN x ( $j_{{\rm{0e,min}}}\,\approx \,{\text{81 fA/ cm}}^{2}$ ) or AlO x /SiN x ( $j_{{\rm{0e,min}}}\,{\rm{\approx}} \,\text{31 fA/ cm}^{2}$ ) if the emitter recombination channels are suppressed. Based upon macroscopic measurement of contact resistivity and microscopic analysis of the contact areas, we propose that the formation of numerous metal–semiconductor direct contact points on the peak and the plateaus of the nanostructures are mainly responsible for a low specific contact resistivity ( $\rho _{{\rm{c,min}}}\,{\rm{\approx}} \,\text{1.2}\; \text{m}\Omega \cdot \text{cm}^{2}$ ) achievable in these surfaces.

We investigate stacks of aluminum oxide (Al2O3) and boron-doped silicon nitride (SiNX:B) layers for the rear side passivation and local doping of p-type silicon solar cell samples aiming for the realization of bifacial passivated emitter and rear locally diffused (biPERL) solar cells. The local p+-doped back surface field regions are formed by laser doping and are electrically contacted using commercially available screen-printed and fired silver-aluminum (AgAl) or silver (Ag) contacts. This approach is referred to as “pPassDop”. Laser doping results in highly-doped silicon with sheet resistances as low as 15 Ω/sq and surface doping concentrations up to 6×1019 cm−3. Low specific contact resistances around 1 mΩ cm2 and 5 mΩ cm2 are measured for the screen-printed and fired AgAl and Ag contacts, respectively. In addition, the influence of each individual layer within the pPassDop layer stack on the doping properties is investigated. In order to separate the impact of aluminum and boron doping, firstly the influence of the Al2O3 layer thickness (0 nm, 4 nm, 6 nm) below the SiNX:B capping layer is studied. Secondly, a conventional undoped SiNX capping layer is applied on a 6 nm-thick Al2O3 layer. The roles of each dopant are studied by measuring the doping profile and contact resistivity.

In this paper, we study the influence of modifying the geometry of nanotexture on its electrical properties. Nanotexture is formed by an industrially feasible dry-chemical etching process performed entirely in atmospheric pressure conditions. A surface modification process is developed that allows low surface recombination velocities ( S eff,min ≤ 10 cm/s) on nanotextured surfaces. By simultaneously improving the surface passivation and the emitter diffusion processes, we achieve an equivalent passivation level ( V OC,impl ≥ 670 mV) for nanotextured surfaces to that of reference textured surfaces after applying either PECVD or ALD based deposition techniques.

Current studies reveal the expectation that photovoltaic (PV) energy conversion will become the front-runner technology to stem against the extent of global warming by the middle of this century. In 2019, the passivated emitter and rear cell (PERC) design has taken over the majority of global photovoltaic solar cell production. The objective of this paper is to review the fundamental physics of the underlying cell architecture, its development over the past few decades to an industry main stream product, as well as an in-depth characterization of current cells and the future potential of the device structure. The early development of PERCs was set by an intriguing series of improvements starting in 1989 and resulting in a long-standing energy conversion efficiency record of 25.0% set up in 1999. It took a decade of intense technological development to implement this structure as an upgrade to existing production lines and another decade to increase the efficiency of industrially manufactured cells to over 22%. Our analysis of state-of-the-art large-area screen-printed PERCs is based on the pilot-line technology in the Photovoltaic Technology Evaluation Center at the Fraunhofer ISE, which is assumed to be representative of current state-of-the art cell processing. The main recent cell efficiency improvements have been achieved thanks to fine line metallization taking advantage of the high quality emitter formation and passivation and to improvements in material quality. In order to enhance the energy yield of the PV modules, innovations in interconnection technology like multibusbar and shingling technology as well as bifaciality are supported by PERC developments. Over the years, ongoing improvements have been made in the understanding of PERCs by analytical and numerical modeling of these devices. We show a study based on 3D numerical modeling and an extrapolation of the PERC device structure and technology to achieve an efficiency of 26%. This result surpasses earlier investigations due to the combination of technology components, as further improved front contact and emitter design as well as rear passivation and mirrors. We expect that PERCs can also play a strong role at the bottom of multijunction solar cells and will defend a strong position in global PV production beyond the end of the now starting decade.

Silicon oxide (SiOx) has many applications, including as a low-refractive index material. Plasma enhanced chemical vapor deposition (PECVD) processes are facile, low temperature routes to produce thin SiOx layers. A route to decrease the refractive index of SiOx films is to increase the layer porosity although maintaining structural and optical stability remains challenging. Organic carbon-containing sacrificial layers have been shown to modify the growth and resulting structure of PECVD SiOx layers. In this work, we study the effect of adding methane (CH4) to the standard SiOx process gas mixture (silane and nitrous oxide) and varying deposition temperatures and microwave power in an industrial-scale, microwave PECVD reactor. Spectral ellipsometry was used to measure the optical properties of deposited layers, Fourier-transformed infrared (FTIR) spectroscopy to determine bonding and the layer porosity, and optical emission spectroscopy to characterize the plasma. We propose two regimes characterized by whether adding CH4 increases or decreases the refractive index and porosity of deposited layers compared to SiOx layers grown under standard conditions. However, the magnitude of the effect of adding CH4 was not large and would not find industrial application. Furthermore, the deposited layers’ refractive indices increased over time, indicating that the effects of adding CH4 to the process gas mixture were not stable. To help explain our results and to provide guidance for future efforts to better control the refractive index of PECVD SiOx layers via carbon incorporation while maintaining layer stability, we propose possible growth pathways for our layers considering both plasma reactions and surface processes.

We demonstrate a bifaciality of 88.0% for 6-inch bifacial p-type Cz-Si passivated emitter and rear cells (biPERC) and increase their rear side energy conversion efficiency to 18.0% by minor adaptions in the fabrication sequence. We utilize the “pPassDop” concept on the cells’ rear side that applies an aluminum oxide and a boron-doped silicon nitride (SiN X :B layer stack for simultaneous passivation and doping source. Laser doping forms the local p-doped back surface field regions for these biPERL solar cells. Screen-printed silver-aluminum metallization contacts these regions. We also demonstrate the compatibility of the laser doping approach with conventional (undoped) SiN X capping layer to fabricate biPERL devices with screen-printed contacts.

We present an approach to analyze and identify the predominant loss mechanisms in silicon solar cells. For this end, all losses are converted to potential efficiency gains and are thus directly comparable to one another as a derivative-like quantity. This derivative-like nature of the gains is validated at the hands of numerical simulations, showing that the formulary of the method basically calculates the derivatives of the efficiency with regard to the input parameters. The approach is solely based on measured data alone and recombination currents are measured at maximum power point like conditions. It is the first method to combine all these characteristics and is exemplarily applied to passivity emitter and rear cells (PERC) based on $p$-type mono- and multicrystalline silicon wafers. For our examined solar cells, we identify as bottlenecks the optical and recombination properties of the front side metallization in case of the monocrystalline PERC cell and the reflection at the active area in the multicrystalline case with potential efficiency gains of $1.2\%_{\mathrm {a}\mathrm {b}\mathrm {s}}$ and $1.6\%_{\mathrm {a}\mathrm {b}\mathrm {s}}$, respectively.

We introduce an approach to analyze and identify the predominant loss mechanisms in silicon solar cells. For this end, we focus on the potential efficiency gains to be acquired by suppressing each loss mechanism. All the losses are scaled to efficiency gains, leading to quantities similar to the derivative of the efficiency with respect to the loss mechanisms. All impacts are directly comparable to one another since the potential gains are quantified in the same units. The approach is solely based on measured data alone and we take injection-dependent lifetimes correctly into account by measuring at maximum power point like conditions. This approach is exemplarily applied to passivated emitter and rear cells (PERC) based on p -type mono- and multicrystalline silicon wafers. For our examined solar cells, we identify as bottlenecks the optical and recombination properties of the front-side metallization in case of the monocrystalline PERC cell and the reflection at the active area in the multicrystalline case with potential efficiency gains of 1.23%abs and 1.56%abs, respectively.

In this paper, we report significant progress in development and integration of a plasma-less atmospheric pressure dry texturing (ADE) process, performed on multicrystalline silicon (mc-Si) wafers, into high efficiency PERC solar cell architectures using industrially applied process steps. The mechanism of forming sub-micron features on monocrystalline and multicrystalline silicon wafers with commercial grade fluorine gas (F2) is briefly presented. Low weighted surface reflection (Rw,min < 10%) is achieved for mc-Si substrates regardless of the wafer sawing method. Mc-Si PERC solar cells with average conversion efficiencies of 20% are fabricated in the industrial pilot line of Hanwha Q-Cells in Thalheim. A detailed characterization of ADE-textured solar cells suggest that an enhancement in conversion efficiency of up to +0.8% absolute is possible in comparison to the reference-textured solar cells by narrowing the distribution of reflectivity in the textured wafer surface.

The performance of PERC solar cells benefits from a smooth rear surface due to a reduced surface recombination and increased light trapping. State of the art surface roughness is defined solely by the polishing silicon removal. However the initial texture height can vary, therefore there is no universal definition of roughness. In this work roughness parameters from an earlier study will be used to determine the rear surface roughness of mono-crystalline industrial p-type solar cells [1]. The effects of rear side roughness on the passivation quality and thus minority carrier lifetime will be discussed. Additionally the influence of rear side roughness on reflection and therefore light trapping will be investigated. Furthermore solar cells with PERC concept are presented. Up to now used roughness parameters describe vertical structures and thus represent polishing results but they are not sensitive to horizontal structure expansion. Effective lifetime of polished samples first increases with decreasing roughness. For further polishing values stagnate or decrease. Implied VOC of saw damage etched surface is higher compared to polished surface although they show similar vertical roughness, hence there are more parameters influencing passivation quality than vertical roughness. According to roughness measurements nano-roughness, valleys and horizontal structure expansion seem to affect passivation quality in addition to vertical roughness. Decreasing roughness increases reflection at 1200 nm and thus increases light trapping. As the highest benefit in light trapping appears with decreasing structure height, vertical structure expansion seems to affect back reflection less than horizontal structures. Solar cell results cannot confirm the results of implied VOC and reflection measurements but prove the benefit of smooth rear sides. For polished polished rear sides the gain in efficiency is decreasing with increasing silicon removal.

Reducing wafer thickness while increasing power conversion efficiency is the most effective way to reduce cost per Watt of a silicon photovoltaic module. Within the European project 20 percent efficiency on less than 100-mu m-thick, industrially feasible crystalline silicon solar cells ("20pl mu s"), we study the whole process chain for thin wafers, from wafering to module integration and life-cycle analysis. We investigate three different solar cell fabrication routes, categorized according to the temperature of the junction formation process and the wafer doping type: p-type silicon high temperature, n-type silicon high temperature and n-type silicon low temperature. For each route, an efficiency of 19.5% or greater is achieved on wafers less than 100 mu m thick, with a maximum efficiency of 21.1% on an 80-mu m-thick wafer. The n-type high temperature route is then transferred to a pilot production line, and a median solar cell efficiency of 20.0% is demonstrated on 100-mu m-thick wafers. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

In this contribution, negative charges and electronic traps related to the Si/Al2O3 interface were measured and related to paramagnetic point defects and molecular vibrations. To this end, contactless capacitance voltage measurements, X-band electron paramagnetic resonance (EPR), and infrared spectroscopy were carried out, and their results were compared. A change in the negative charge density and electron trap density at the Si/Al2O3 interface was achieved by adding a thermally grown SiO2 layer with varying thicknesses and conducting an additional temperature treatment. Using EPR, five paramagnetic moments were detected in Si/(SiO2)/Al2O3 samples with g values of g1 = 2.0081 ± 0.0002 , g2 = 2.0054 ± 0.0002 , g3 = 2.0003 ± 0.0002 , g4 = 2.0026 ± 0.0002, and g5 = 2.0029 ± 0.0002. Variation of the Al2O3 layer thickness shows that paramagnetic species associated with g1, g2, and g3 are located at the Si/Al2O3 interface, and those with g4 and g5 are located within the bulk Al2O3. Furthermore, g1, g2, and g3 were shown to originate from oxygen plasma exposure during Al2O3 deposition. Comparing the g values and their location within the Si/Al2O3 system, g1 and g3 can be attributed to Pb0 centers, g3 to Si dangling bonds (Si-dbs), and g4 and g5 to rotating methyl radicals. All paramagnetic moments observed in this contribution disappear after a 5-min temperature treatment at 450 ° C. The deposition of an additional thermal SiO2 layer between the Si and the Al2O3 decreases the negative fixed charge density and defect density by about one order of magnitude. In this contribution, these changes can be correlated with a decrease in amplitude of the Si-db signal. Pb0 and the methyl radical signals were less affected by this additional SiO2 layer. Based on these observations, microscopic models for the negative fixed charge density (Qtot) and the interface trap density (DQit) and the connection between these values are proposed.

In this work, we present a systematic study of the surface recombination velocity of boron-diffused Si wafer passivated with plasma-enhanced chemical-vapor-deposited (PECVD) AlO x layers. Saturation current densities in the range of 5.2–38 fA cm − 2 (at 300 K) were achieved on planar surfaces. In particular, we present an industrially relevant boron emitter, allowing for about 700 mV open circuit voltage on textured surfaces, after a firing process. This high passivation quality could be achieved using AlO x passivation layers deposited by PECVD. The passivation quality is found to be equivalent to AlO x layers deposited by plasma-assisted atomic-layer-deposition. A wide range of surface doping concentration (2.5–70 × 10 18 cm − 3 ) was investigated. The emitters used here allow a high resolution in the determination of the surface recombination velocity upper limit. Our simulations, based on Fermi-Dirac statistics, indicate that only very shallow emitters can be used to further increase the resolution on the determination of the surface recombination velocity.

We present small-area metal wrap through solar cells with passivated rear side (MWT-PERC), screen-printed metallization, and a homogeneous industrial-like emitter showing an efficiency of 20.2%. A comparison of H-pattern reference cells and cells with aluminum back surface field confirms the advantages of the MWT-PERC approach and reveals significant synergistic effects of rear-surface passivation and wrap through metallization.

This paper is revisiting the problem of recombination on locally processed area (contacts, local doping …), based on the concept of point recombination rate (pLPA). The newly introduced effective point recombination rate (peff) can be easily determined from the effective surface recombination velocity. It also allows predictions and comparisons in most of the practical cases. Further analysis allows the separation of the influence of pLPA from the one of the transport of the carrier in a transparent way. Due to its simplicity, transparency and accuracy, the model proposed here is believed to be more suitable to recent local processing technology than the existing analytical models.

We investigate local defects in rear passivation layers, in which the metal is forming a contact to silicon pinning through an insulating layer. At first, we studied these contacts by measuring the layer resistivity of different dielectrics sandwiched between Al and Si. Our study includes the influence of parameters like the surface roughness, the metallization techniques and the post-metallization annealing. In addition, we propose a characterization of these contacts on solar cell level, using photoluminescence-imaging performed before the finalization of the rear contacts. A good correlation between the contacts and the dark saturation current density suggests that these contacts can harm the rear surface passivation quality.

The authors discuss industry related approaches at Fraunhofer ISE for bifacial p-type silicon solar cells, taking into account the well-known "passivated emitter and rear cell" (PERC), "passivated emitter and rear totally diffused" (PERT) and "passivated emitter and locally diffused" (PERL) architectures. In the case of PERC, challenges in terms of alignment, printability and the importance of bifaciality are addressed. In the case of PERT, a co-diffusion process is utilized to form the emitter and the back surface field simultaneously avoiding also critical shunts that can arise at the edges of such devices. For the PERL technology, the industrial feasible pPassDop approach is discussed. We report on front side energy conversion efficiencies for PERC of 21.4%, PERT of 20.5%, and PERL of 19.8%. Furthermore, bifaciality factors for PERC of 0.7, for PERT of 0.86, and for PERL of 0.89 are presented.

We present an analytical model for the internal resistance of passivated emitter and rear totally diffused (PERT) solar cells. First, we apply the model of Saint-Cast for the spreading resistance of a passivated emitter and rear cell (PERC) structure with line-shaped contacts. To account for the additional vertical current flow through the silicon wafer and the lateral current flow through the back surface field of a PERT structure, we add a parallel current path using common analytical expressions. We compare the analytical models with two-dimensional numerical simulations based on Quokka 3 and find deviations of less than 6% for the internal resistance. In addition, we compare the analytical model of the internal resistance of PERC and PERT solar cells with experimental data of the series resistance of PERC and PERT solar cells.

The state-of-the-art low-ohmic electrical contacting of highly boron-doped silicon surfaces is based on the use of screen-printed and fired silver-aluminum (Ag-Al) contacts. For these contacts, metal crystallites with depths of up to a few microns are observed at the interface. For screen-printed and fired Ag contacts on phosphorus-doped surfaces, the observed crystallite depths are much smaller. In this work, low-ohmic electrical contacting of local laser-doped p-type silicon surfaces with commercial pure Ag screen-printing paste are demonstrated. The doping layer is based on the "pPassDop" approach, which serves as a passivation layer on the rear side of p-type silicon solar cells. The specific contact resistances are measured down to 1 mu ohmb cm2 for p-type doping densities of about 3Ã1019cm-3 at the silicon surface and finger widths of around 55 mu m. Microstructure analysis reveals the formation of numerous small Ag crystallites at the interface with penetration depths o f less than 80nm. A first implementation of the "pPassDop" approach on 6-inch p-type Cz-Si bifacial solar cells using solely Ag contacts on both sides results in a peak front side energy conversion efficiency of 19.1%, measured on a black chuck with contact bars on both sides.

The loss analysis of state-of-the-art p-type Czochralski-grown silicon passivated emitter and rear solar cells (PERC) fabricated in a manner close to industrial production is presented in this paper. The 6-inch solar cells are featuring a homogeneous emitter on the front side, an Al2O3 passivation layer and local contacts on the rear side. The peak energy conversion efficiencies obtained are 21.1% for a standard antireflection coating (ARC) and 21.4% for a double-layer ARC. The loss analysis is based on an extended characterization of the solar cells and of special samples, which allow the separation of the contributions of each region of the solar cell including metallization. Their impact is determined experimentally on the open-circuit voltage, the short-circuit current density, and the fill factor. Based on the measurements, the devices are numerically simulated. The free energy losses are analyzed using the simulation model. Based on the results from the loss analysis, it is found that the integration of a selective emitter structure and the further improvement of the rear surface would allow for efficiencies above 22% in the short term.

A study of the thermally activated negative fixed charges Qtot and the interface trap densities Dit at the interface between Si and thermal atomic-layer-deposited amorphous Al2O3 layers is presented. The thermal activation of Qtot and Dit was conducted at annealing temperatures between 220 °C and 500 °C for durations between 3 s and 38 h. The temperature-induced differences in Qtot and Dit were measured using the characterization method called corona oxide characterization of semiconductors. Their time dependency were fitted using stretched exponential functions, yielding activation energies of EA = (2.2 ± 0.2) eV and EA = (2.3 ± 0.7) eV for Qtot and Dit, respectively. For annealing temperatures from 350 °C to 500 °C, the changes in Qtot and Dit were similar for both p- and n-type doped Si samples. In contrast, at 220 °C the charging process was enhanced for p-type samples. Based on the observations described in this contribution, a charging model leading to Qtot based on an electron hopping process betwe...

We are studying the thermal stability of thick hydrogenated amorphous aluminum oxide (Al2O3) layers (20-50 nm) prepared by a high-throughput plasma-enhanced chemical-vapor-deposition (PECVD) technique for the electrical passivation of crystalline silicon surfaces. These passivation layers can be applied alone or covered by a capping layer like amorphous hydrogenated silicon nitride (SiNx) or amorphous hydrogenated silicon oxide (SiOx), also prepared by PECVD. After firing at 870 degrees C for approximately 3 s, the layers show blistering for Al2O3 of 30 nm or higher, independently from the capping layer. For thinner Al2O3, no blistering can be observed even using scanning electron microscope (SEM). Very long carrier lifetimes up to 900 mu s was obtained in passivated p-Si (1 Omega cm) wafer after annealing and firing, without observing a strong influence of the layer thickness and the capping layer. All the layer stacks, including the stacks with SiNx capping layer, show high negative charge densities in the layer (1-4 x 10(12) cm(-2)). Additionally, low interface defect densities (similar to 10(11) cm(-2) eV(-1)), which could be achieved with and without a hydrogenated capping layer, were measured even after firing. To explain these phenomena, hydrogen concentration depth profiles were measured by nuclear reaction analysis. These measurements have shown that, at the Al2O3-Si interface, hydrogen atomic concentration ranging 5-7% after annealing and 4% after firing are obtained independently from the capping hydrogen concentration. We conclude that PECVD Al2O3 layers of 20 nm or thicker can provide enough hydrogen to passivate the interface defects, even after a high te! mperature step. However, the layer thickness should be limited to 30 nm in order to avoid the blistering.

We investigate the role of a few nm thin thermal oxide films in PECVD passivation layer systems. Our results show that an intermediate thermal oxide layer located between the Si substrate and the PECVD layers has a strong impact on the interface properties. Capacitance-voltage measurements reveal that for Al 2 O 3 and SiN X passivation layers, the oxide film lowers or suppresses the formation of fixed charges. Adjusting the oxide film thickness therefore permits the control of band bending and thus field effect passivation at the interface. For SiO X capping layers, a thermal oxide thickness of a few nm is sufficient to reduce the interface trap density, enabling surface recombination velocities as low as a few cm/s.

For the passivation of p-type silicon surfaces, we investigate layer systems consisting of a thin layer of thermally grown SiO2 and different dielectric capping layers deposited by means of plasma-enhanced chemical vapor deposition (PECVD). We find that the thermal SiO2 layer thickness strongly impacts the passivation quality and interface parameters of the stacks. Capacitance-voltage measurements reveal that for Al2O3 and SiNx capping layers, an increased thermal SiO2 film thickness suppresses charge formation at the interface between SiO2 and the capping layer. Interface trap density and effective carrier lifetime data suggest that a certain thermal SiO2 thickness is required to achieve appropriate chemical passivation. The combination of a thin thermal SiO2 layer (~4 nm) and a PECVD-SiOx capping results in very low surface recombination velocities of a few centimeters per second, measured on p-type 1-omega·cm float-zone silicon after contact firing and postmetallization annealing. The experimentally observed dependence of the surface recombination velocity on the fixed charge density, gate voltage, and injection density is reproduced very accurately by analytical calculations that use the measured interface trap density and total charge density at the Si/insulator interface. The model also includes additional recombination in the space charge region of inverted surfaces.

In this paper an analytical model of the effective recombination (S-eff) on the back surface of locally contacted solar cell is developed. We justify this approach by first showing that the three-dimensional (3D) problem can be reduced to a one-dimensional (1D) problem by calculating S-eff. The values of S-eff calculated with our model and two existing models are compared to finite element simulations. A large range of cases from high to low scale structures, including variation in the surface recombination velocity at the passivated area are investigated. The model presented in this paper is in good agreement with finite element simulations. Existing models from literature are also compared to finite element simulations, showing some of their limitations. In addition, we propose a method, not restricted to dark conditions, that simulates the 3D locally contacted structures by means of two 1D simulations.

Ultrathin (7 nm) atomic layer deposited Al2O3 layers and high-deposition-rate plasma-enhanced chemical vapor deposited AlOx layers have been applied and characterized as rear-surface passivation for high-efficiency silicon solar cells. The excellent efficiency values (up to 21.3%-21.5%) demonstrate that both aluminum oxide deposition processes have a very high potential comparable to the reference cells with SiO2 passivation. The high voltages (similar to 680 mV), the excellent long-wavelength quantum efficiency, and the high short-circuit currents of these cells (similar to 40 mA/cm(2)) are a proof for the low rear-surface recombination velocity and excellent internal rear-surface reflection.

Aluminum oxide layers can provide excellent passivation for lowly and highly doped p-type silicon surfaces. Fixed negative charges induce an accumulation layer at the p-type silicon interface, resulting in very effective field-effect passivation. This paper presents highly negatively charged (Q(ox)=-2.1 X 10(12) cm(-2)) aluminum oxide layers produced using an inline plasma-enhanced chemical vapor deposition system, leading to very low effective recombination velocities (similar to 10 cm s(-1)) on low-resistivity p-type substrates. A minimum static deposition rate (100 nm min(-1)) at least one order of magnitude higher than atomic layer deposition was achieved on a large carrier surfaces (similar to 1 m(2)) without significantly reducing the resultant passivation quality.

Recently we reported the possibility of using the room temperature plasma oxidation mechanism to obtain ultrathin silicon oxide films. The oxidation process in O2 and N2O can be modeled by power law dependence with time and is inversely proportional with pressure. On that work, the parameters that modeled the oxidation process were fitting parameters and were analyzed independently for each gas. In present work we derived a general expression to model plasma oxidation processes. In addition, the dependence of the oxidation rate with pressure and temperature were further specified so they are associated to physical mechanisms. Comparison of experimental curves with modeled, using this general expression, is presented.

This work presents a detailed study of c-Si/Al2O3 interfaces of ultrathin Al2O3 layers deposited with atomic layer deposition (ALD), and capped with SiNx layers deposited with plasma-enhanced chemical vapor deposition. A special focus was the characterization of the fixed charge density of these dielectric stacks and the interface defect density as a function of the Al2O3 layer thickness for different ALD Al2O3 deposition processes (plasma-assisted ALD and thermal ALD) and different thermal post-deposition treatments. Based on theoretical calculations with the extended Shockley–Read–Hall model for surface recombination, these interface properties were found to explain well the experimentally determined surface recombination. Thus, these interface properties provide fundamental insights into to the passivation mechanisms of these Al2O3/SiNx stacks, a stack system highly relevant, particularly for high efficiency silicon solar cells. Based on these findings, it was also possible to improve the surface passi...

In this publication, the activation and degradation of the passivation quality of plasma-enhanced chemical vapor deposited aluminum oxide (Al2O3) layers with different thicknesses (10 nm, 20 nm, and 110 nm) on crystalline silicon (c-Si) during long and high temperature treatments are investigated. As indicated by Fourier Transform Infrared Spectroscopy, the concentration of tetrahedral and octahedral sites within the Al2O3 layer changes during temperature treatments and correlates with the amount of negative fixed charges at the Si/Al2O3 interface, which was detected by Corona Oxide Characterization of Semiconductors. Furthermore, during a temperature treatment at 820 °C for 30 min, the initial amorphous Al2O3 layer crystallize into the γ-Al2O3 structure and was enhanced by additional oxygen as was proven by x-ray diffraction measurements and underlined by Density Functional Theory simulations. The crystallization correlates with the increase of the optical density up to 20% while the final Al2O3 layer th...

This paper focusses in particular on the influence of the layer thickness on the passivation quality, the charge density and the interface defects of PECVD Al 2 O 3 passivation layers on c-Si surfaces. The surface recombination velocity and the interface defect density are observed to increase by decreasing the layer thickness. However, the density of negative charges remains almost constant with values around 3 1012 cm-2. An optimal passivation quality is obtained for thicknesses of 15 nm and higher. A linear relation between surface recombination velocity and Dit was established, allowing the estimation of the electron capture cross section (σ n ∼ 10 -13 cm -2 ). Additionally, we measured the capture cross section of holes and electrons using DLTS measurement. The results are found to be very similar to reported values for silicon dioxide. This supports the idea that the chemical passivation of crystalline silicon by Al2O3 is performed by the interstitial SiO2 layer.

We present a detailed study about the influence of post-deposition temperature treatment on PECVD Al2O3 passivation layers. Fourier transform infrared spectroscopy (FTIR) and quasi-steady-state photoconductance (QSSPC) were applied for characterization. We observed several indications of structural changes of the Al2O3 layer with annealing duration, temperature and layer thickness. A shift and an increase of the Si-O vibrational mode (1100980 cm -1 ) in the FTIR measured with changing temperature and layer thickness is presented. Structural changes of the Al2O3 layer with annealing duration, temperature, and layer thickness, caused by changes in the oxygen concentration within the SiOx layer are observed for the different FTIR spectra. We also detected a water band at 1650-1630 cm -1 and other OH components around 3200 cm -1 -400cm -1 depending on annealing temperature and time. For a temperature of 820°C, a dramatic change of the Al2O3 peak (650-700 cm -1 ) is observed. This is probably due to the crystallization of the film. © 2012 Published by Elsevier Ltd. Selection and peer-review under responsibility of the scientific committee of the SiliconPV 2012 conference