Field-effect Passivation Research Articles

Application of SiOxNy films in industrial bifacial PERC solar cells

The bifacial p-type silicon (p-Si) passivated emitter and rear cells (PERCs) have dominated the industrial bifacial solar cells. In this paper, we have investigated the impact of hydrogenated amorphous silicon oxynitride (SiOxNy) films on the optical and electrical performance of bifacial p-Si PERCs. Simulation and characterization are carried out to show the improvement of bifacial p-Si PERCs, yielding an absolute front-side efficiency improvement of 0.14% and 016% with SiOxNy films introduced to the front-side and rear-side, respectively. When SiOxNy films are employed to both sides of bifacial p-Si PERCs, the front-side and rear-side efficiency separately increase by 0.27% and 0.26% compared to the baseline without SiOxNy films. We have achieved on the bifacial p-Si PERCs production line an averaged front-side efficiency of 23.23% (champion efficiency of 23.42%), together with a 17.31% averaged rear-side efficiency. Furthermore, the introduction of SiOxNy films has been demonstrated to reduce the rear-side potential induced degradation (PID) effect through both single-cell modules and commercial glass-glass modules, due to the SiOxNy films protecting AlOx from corrosion and maximizing the field-effect passivation of AlOx layers.

Correlative analysis of embedded silicon interface passivation by Kelvin probe force microscopy and corona oxide characterization of semiconductor.

We report a correlative analysis between corona oxide characterization of semiconductor (COCOS) and Kelvin probe force microscopy (KPFM) in a study of embedded silicon surfaces in the field of chemical and field-effect passivation. The COCOS approach gives access to the defect density, the total charge contained in the passivation stack, and the potential barrier. Based on the COCOS parameters, we could probe by KPFM to analyze the influence of the passivation stack upon the surface photovoltage. Thus, KPFM emerges as a valuable method to access chemical and field-effect passivation directly. We confirm that it is possible to differentiate by KPFM the influence of local band bending (i.e., field-effect passivation) from the effects due to the local recombination rates (i.e., chemical passivation). The measurements were carried on five different passivation layers of different thicknesses, precisely, 10.5nm SiO2, 50nm SiN, 7nm Al2O3, 7nm HfO2, and a double layer of 7nm Al2O3 below 53nm Ta2O5. Based on our correlative analysis, we could identify by KPFM that HfO2 displays the best chemical passivation properties. Additionally, we confirm that using an anti-reflective coating such as a Ta2O5 layer on top of Al2O3 causes the chemical passivation to deteriorate. Finally, for p-type silicon, SiN appears to be the worst case in terms of field-effect passivation.

Analyses and Excess Oxygen Investigations by Scanning Transmission Electron Microscopy and Electron Energy Loss Spectroscopy at AlOx/Si Interfaces in Passivated Emitter and Rear Solar Cells

Progressive optimization of the surface passivation of Si solar cells requires access to the elemental composition and chemical bonding characteristics of ultrathin layers and buried interfaces on textured or structured surfaces. The passivation of the rear side of passivated emitter and rear solar cells, for instance, can be realized through AlOx/SiNx stacks, which are known to provide an additional field effect passivation on top of the chemical surface passivation. Herein, transmission electron microscopy is used at locally prepared cross‐sections of such stacks. Electron energy loss spectroscopy is used to extract depth‐resolved information of elemental composition and chemical bonding at nanometer scale. With this, the interfacial excess O fraction, which is crucial for the field effect passivation, is successfully determined for the first time for AlOx passivation layer systems on industrially produced Si solar cells.

Field-Effect Passivation of Undiffused Black Silicon Surfaces

Black silicon (b-Si) surfaces typically have a high density of extreme nanofeatures and a significantly large surface area. This makes high-quality surface passivation even more critical for devices such as solar cells with b-Si surfaces. It has been hypothesized that conformal dielectrics with a high fixed charge density ( <b xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</b> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><b>f</b></sub> ) are preferred as the nanoscale features of b-Si result in a significant enhancement of field-effect passivation. This article uses 1-D, 2-D, and 3-D numerical simulations to study surface passivation of b-Si, where we particularly focus on the charge carrier control by | <b xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</b> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><b>f</b></sub> | up to 1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> under accumulation conditions. We will show that there is a significant space charge region compression in b-Si nanofeatures, which affects the charge carrier population control for moderate | <b xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</b> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><b>f</b></sub> | up to ≈1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> . The average surface minority charge carrier density can be reduced by 70% in some cases, resulting in an equivalent reduction in area-normalized surface recombination losses if the effective surface recombination velocity ( <b xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</b> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> ) is limited by minority carriers. This provides a possible solution for the empirical <b xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</b> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> ∝ 1/ <b xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</b> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><b>f</b></sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> reported previously. We will also show that the situation is more complicated for surface passivation films where the ratio between the electron and hole capture cross section (σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><b>n</b></sub> / σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><b>p</b></sub> ) is higher than 10 for p-type surfaces. For commonly used surface passivation films with a | <b xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</b> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><b>f</b></sub> | larger than ≈1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> , there is little space charge compression for b-Si. Consequently, <b xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</b> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> simply scales with the surface area, i.e., there is no enhanced reduction of surface recombination by field-effect passivation on b-Si.

Achieving high-responsivity near-infrared detection at room temperature by nano-Schottky junction arrays via a black silicon/platinum contact approach

A room temperature sub-bandgap near-infrared ( λ &gt; 1100 nm ) Si photodetector with high responsivity is achieved. The Si photodetector features black Si made by wet etching Si (100), Si/PtSi nano-Schottky junction arrays made from black Si/Pt contacts, and chemical and field-effect passivation of black Si. Responsivities are 147.6, 292.8, and 478.2 mA/W at reverse voltages of − 1.0 , − 1.5 , and − 2.0 V for 1550 nm light, respectively, with corresponding specific detectivities being 9.79 × 10 8 , 1.88 × 10 9 , and 2.97 × 10 9 cm · Hz 1 / 2 / W . This work demonstrates a practical room temperature sub-bandgap near-infrared Si photodetector that can be made in a facile and large-scale manner.

Time‐Resolved Investigation of Transient Field Effect Passivation States during Potential‐Induced Degradation and Recovery of Bifacial Silicon Solar Cells

Various types of potential‐induced degradation (PID) with fundamentally different physical root causes have been observed recently ranging from shunting (PID‐s), corrosion (PID‐c) to degradation of surface passivation (PID‐p). Herein, PID‐p is investigated for the first time at the rear side of bifacial silicon solar cells with enhanced time‐resolution during degradation and recovery under simultaneous illumination. The tests reveal fast transient changes of rear‐side short‐circuit current within minutes and thus allow to understand the degradation process related to PID‐p. The short‐circuit current with rear‐side illumination first decreases significantly by more than 80 % resulting in an intermediate degraded state. Subsequently, it increases to a regenerated state. Under reversed bias, a total recovery of the cell parameters is observed and confirmed by I–V measurements under standard testing conditions (STCs). The underlying transient PID‐p degradation and recovery mechanism is well described by a PC‐1D simulation of the field‐induced band bending at the rear surface. Finally, a qualitative model involving the migration of mobile charged species and their impact on the charge equilibrium in the field effect passivation layer is presented. Thus, time‐resolved analysis of transient PID effects can serve as a clear characteristic for PID of polarization type.

Passivating antireflection coating of crystalline silicon using i/n a-Si:H/SiN trilayer

Passivating antireflection coating of crystalline silicon has been experimentally studied using a three-layered stack, consisting of an i/n a-Si:H/SiN trilayer. The passivation property is characterized by the minority carrier lifetime, which shows ≳ 1 ms for the i/n a-Si:H/SiN trilayer prepared at a temperature as low as 250 ∘C. The antireflection property is confirmed by a reflection of light of ≲ 2.0% at 550 nm and a low reflection in a wide range of visible and near-infrared regions, which is adequate for solar cell application, particularly in back-contact structure. The roles of each layer are discussed in terms of the chemical and field-effect passivation as well as the antireflection property. The optoelectronic properties of a neat SiN layer are also discussed to achieve a stable and reliable antireflection performance under the low-temperature growth conditions.

Influence of the Rear Interface on Composition and Photoluminescence Yield of CZTSSe Absorbers: A Case for an Al2O3 Intermediate Layer.

The rear interface of kesterite absorbers with Mo back contact represents one of the possible sources of nonradiative voltage losses (ΔVoc,nrad) because of the reported decomposition reactions, an uncontrolled growth of MoSe2, or a nonoptimal electrical contact with high recombination. Several intermediate layers (IL), such as MoO3, TiN, and ZnO, have been tested to mitigate these issues, and efficiency improvements have been reported. However, the introduction of IL also triggers other effects such as changes in alkali diffusion, altered morphology, and modifications in the absorber composition, all factors that can also influence ΔVoc,nrad. In this study, the different effects are decoupled by designing a special sample that directly compares four rear structures (SLG, SLG/Mo, SLG/Al2O3, and SLG/Mo/Al2O3) with a Na-doped kesterite absorber optimized for a device efficiency >10%. The IL of choice is Al2O3 because of its reported beneficial effect to reduce the surface recombination velocity at the rear interface of solar cell absorbers. Identical annealing conditions and alkali distribution in the kesterite absorber are preserved, as measured by time-of-flight secondary ion mass spectrometry and energy-dispersive X-ray spectroscopy. The lowest ΔVoc,nrad of 290 mV is measured for kesterite grown on Mo, whereas the kesterite absorber on Al2O3 exhibits higher nonradiative losses up to 350 mV. The anticipated field-effect passivation from Al2O3 at the rear interface could not be observed for the kesterite absorbers prepared by the two-step process, further confirmed by an additional experiment with air annealing. Our results suggest that Mo with an in situ formed MoSe2 remains a suitable back contact for high-efficiency kesterite devices.

Understanding the Origin of Recombination Losses After Co-Plating of Bifacial Solar Cells: In-Depth Microstructure Study

Contactless plating with electroless solutions can provide self-aligned high-efficiency contacts with very low silver content, using simple and inexpensive equipment. With prior surface activation, it can even be used to metallize both sides of bifacial silicon solar cells simultaneously. However, we observe in such a coplating process with nickel, where surface activation is achieved by immersion plating and thickening by electroless plating, that V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</sub> and fill factor can sometimes significantly decrease with immersion-plating time. To understand the reason for this electrical degradation, we studied the impact of immersion plating on the microstructure of the plated silicon surface. The evolution of the Si-Ni interface was studied by scanning and transmission electron microscopies, energy-dispersive X-ray analysis, secondary ion mass spectrometry, and scanning spreading resistance microscopy. Our attention focused on metal in-diffusion, silicon roughening and etching as the origin for increased recombination. Etching was found to have a significant impact on V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</sub> . The thickness of N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> Si etched during Ni deposition can in fact suppress in a few locations most of the field-effect passivation underneath the contacts. This means that a thicker surface field with doping beyond 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sup> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> must be foreseen under the plated areas, or that the amount of Si lost in the reaction must be reduced. Our observations also confirm that immersion plating can hinder silicide formation and allow Ni in-diffusion, which may be a concern for reliability.

Silicon homo-hetero junction solar cell: An analytical approach for modeling and characterization of the amorphous/crystalline silicon heterostructure

In this paper, an analytical model is presented to study the physical aspects and properties of a novel silicon solar cell structure consisting of both heterojunction and homojunction at the front and back surfaces. The front surface stack consists of (p + )a-Si:H/(i)a-Si:H/(p + )c-Si/(n)c-Si layers and the back surface stack consists of (n + )a-Si:H/(i)a-Si:H/(n + )c-Si/(n)c-Si layers. The analytical model for electrical field, and surface potential in a-Si:H/c-Si interfaces is validated by numerical simulations. The impact of doping concentration and thickness of the buffer layers, density of states in interface defects and in the bulk of a-Si:H layers, is investigated, using the developed model. The results show that using a 10 nm thick (p + )c-Si with doping concentration of 1×1019cm-3, the electric field increases approximately twice in the front surface of (n)c-Si. Also similar results is obtained for the back surface interfaces, and 70% increase in electric field is obtained using a 10 nm (n + )c-Si layer with doping concentration of 1×1019cm-3. It is shown analytically that due to field passivation enhancement on both solar cell’s surfaces using the buffer layers can reduce the sensitivity of surface potential to interface defect densities. The model describes increasing field effect passivation and less sensitivity of surface potential to interface defect densities as the main elements in boosting the solar cell performance.

STEM-EELS investigation of c-Si/a-AlOx interface for solar cell applications

In this article, STEM-EELS methodology is described to investigate the composition of sensitive crystalline Silicon/amorphous aluminum oxide (c-Si/a-AlOx) interface of an a AlOx/amorphous hydrogenated silicon nitride (a-AlOx/a-SiNx:H) passivation stack of a c-Si solar cell. In this stack, a-AlOx has the distinctive characteristic to provide both chemical and field effect passivation, which need further research to be more controlled in order to improve solar cell efficiency. a-AlOx is known to be unstable under the electron-beam, so we first present a detailed study on the electron-beam radiation damage to c-Si/a-AlOx interface. This interface can indeed undergo several electron-beam irradiation damage like sputtering, knock-on or radiolysis if precautions are not taken. Radiolysis damage has been found to be the dominant radiation damage. Thus, several STEM-EELS acquisition parameters like acceleration voltage, electron dose and scan orientation were taken into account and modified to limit this radiolysis damage. Once the irradiation was limited, STEM-EELS investigation was conduct using DualEELS on the Si and Al L2,3 and OK edge fines structures. The interface was found to be composed of a-SiOx and non-stoichiometric aluminum silicate with a predominance of tetrahedrally coordinated Al in its first layer.

Role of ALD Al2O3 Surface Passivation on the Performance of p-Type Cu2O Thin Film Transistors.

High-performance p-type oxide thin film transistors (TFTs) have great potential for many semiconductor applications. However, these devices typically suffer from low hole mobility and high off-state currents. We fabricated p-type TFTs with a phase-pure polycrystalline Cu2O semiconductor channel grown by atomic layer deposition (ALD). The TFT switching characteristics were improved by applying a thin ALD Al2O3 passivation layer on the Cu2O channel, followed by vacuum annealing at 300 °C. Detailed characterization by transmission electron microscopy-energy dispersive X-ray analysis and X-ray photoelectron spectroscopy shows that the surface of Cu2O is reduced following Al2O3 deposition and indicates the formation of a 1-2 nm thick CuAlO2 interfacial layer. This, together with field-effect passivation caused by the high negative fixed charge of the ALD Al2O3, leads to an improvement in the TFT performance by reducing the density of deep trap states as well as by reducing the accumulation of electrons in the semiconducting layer in the device off-state.

Full-scale chemical and field-effect passivation: 21.52% efficiency of stable MAPbI3 solar cells via benzenamine modification

Full-scale chemical and field-effect passivation: 21.52% efficiency of stable MAPbI3 solar cells via benzenamine modification

Light-Promoted Electrostatic Adsorption of High-Density Lewis Base Monolayers as Passivating Electron-Selective Contacts.

Achieving efficient passivating carrier‐selective contacts (PCSCs) plays a critical role in high‐performance photovoltaic devices. However, it is still challenging to achieve both an efficient carrier selectivity and high‐level passivation in a sole interlayer due to the thickness dependence of contact resistivity and passivation quality. Herein, a light‐promoted adsorption method is demonstrated to establish high‐density Lewis base polyethylenimine (PEI) monolayers as promising PCSCs. The promoted adsorption is attributed to the enhanced electrostatic interaction between PEI and semiconductor induced by the photo‐generated carriers. The derived angstrom‐scale PEI monolayer is demonstrated to simultaneously provide a low‐resistance electrical contact for electrons, a high‐level field‐effect passivation to semiconductor surface and an enhanced interfacial dipole formation at contact interface. By implementing this light‐promoted adsorbed PEI as a single‐layered PCSC for n‐type silicon solar cell, an efficiency of 19.5% with an open‐circuit voltage of 0.641 V and a high fill factor of 80.7% is achieved, which is one of the best results for devices with solution‐processed electron‐selective contacts. This work not only demonstrates a generic method to develop efficient PCSCs for solar cells but also provides a convenient strategy for the deposition of highly uniform, dense, and ultra‐thin coatings for diverse applications.

The impact of deposition and annealing temperature on the growth properties and surface passivation of silicon dioxide films obtained by atomic layer deposition

This paper studies the impact of deposition and annealing temperature on the growth properties and surface passivation of silicon dioxide (SiO2) films obtained by atomic layer deposition (ALD) using tris(dimethylamino)-silane (TDMAS) precursor. Increasing in deposition temperature from 200 to 350 °C alters the growth rate and refractive index significantly. The ALD-SiO2 films deposited at over 250 °C obtain excellent surface passivation after annealing at 650 °C, which could be explained by the synergistic effects of chemical and field-effect passivation caused by low interface defect states density (Dit) and high positive fixed charges density (Qf), respectively. Meanwhile, the effect of deposition temperature on surface passivation depends on the extent of TDMAS chemical adsorption and dissociation during ALD. X-ray photoelectron spectroscopy (XPS) shows low temperature as-deposited SiO2 films contain higher carbon impurities because of the remained dimethylamine groups. Regarding the impact of annealing temperature on surface passivation, secondary ion mass spectroscopy profiles and XPS results reveal that high-temperature annealing probably forms more hydrogen and oxygen vacancies at SiO2/Si interface, causing a decrease in Dit and an increase in positive Qf, respectively. This work provides a reference for applying ALD-SiO2 films to surface passivation technology of crystalline silicon solar cells.

Evolution of the surface passivation mechanism during the fabrication of ex-situ doped poly-Si(B)/SiOx passivating contacts for high-efficiency c-Si solar cells

Passivating the contacts of crystalline silicon (c-Si) solar cells (SC) with a poly-crystalline silicon (poly-Si) layer on top of a thin silicon oxide (SiOx) is currently sparking interest for reducing carrier recombination at the interface between the metal electrode and the c-Si substrate. However, due to the interrelation between different mechanisms at play, a comprehensive understanding of the surface passivation provided by the poly-Si/SiOx contact in the final SC has not been achieved yet. In the present work, we report on an original ex-situ doping process of the poly-Si layer through the deposition of a B-rich dielectric layer followed by an annealing step to diffuse B dopants in the layer. We propose an in-depth investigation of the passivation scheme of the resulting B-doped poly-Si/SiOx contact by first comparing the surface passivation provided by ex-situ doped and intrinsic poly-Si/SiOx contacts at different steps of the fabrication process. The excellent surface passivation properties obtained with the ex-situ doped poly-Si(B) contact (iVoc = 733 mV and J0 = 6.1 fA cm−2) attests to the good quality of this contact. We then propose further STEM, ECV and ToF-SIMS characterizations to assess: i) the evolution of the microstructure and B-doping profile through ex-situ doping and ii) the diffusion profile of hydrogen in the poly-Si contact. Our results show a gradual filling of the poly-Si layer with active B dopants with increasing annealing temperature (Ta), which strengthens the field-effect passivation and enables an iVoc increase after annealing up to 800 °C. We also observe a diffusion of O from the SiON:B doping layer to the interfacial SiOx layer during annealing, that likely enhances the passivation stability of our ex-situ doped poly-Si contact with increasing Ta. Finally, we conclude that the mechanism dominating the surface passivation changes during the fabrication process of the poly-Si/SiOx contact from field-effect passivation after annealing (performed for B-diffusion in the contact) to chemical passivation after following hydrogenation of the samples (performed by depositing a H-rich silicon nitride layer).

Investigation of silicon surface passivation by sputtered amorphous silicon and thermally evaporated molybdenum oxide films using temperature- and injection-dependent lifetime spectroscopy

Crystalline silicon (c-Si) surface passivation has been investigated by sputtered hydrogenated intrinsic amorphous silicon (S-i-a-Si:H) and thermally evaporated molybdenum oxide (MoOx) thin films. The temperature- and injection-dependent lifetime spectroscopy technique has been adopted for analyzing the passivation quality of the c-Si surface, using parameters such as the minority carrier effective lifetime (τeff), the activation energy of surface/interface defect states (ΔE), and the electron to hole carrier capture cross-section ratio (k) at the interface. With S-i-a-Si:H films, a τeff of ∼70 µs and ΔE of ∼51 meV have been observed in comparison to a τeff of ∼110 µs and ΔE of ∼109 meV from the MoOx films. These entirely different parameters are an indication of the relatively strong carrier recombination with dense interface/surface states from the S-i-a-Si:H passivation layers. The S-i-a-Si:H layers are unable to minimize the c-Si surface trap states with the chemical passivation for reducing carrier recombination due to the generation of additional surface defect states by the sputtering damage. However, the MoOx layers show better c-Si surface passivation due to the reduction of majority carriers by the carrier inversion (field-effect passivation) and chemical passivation. This effect is clearly reflected with the opposite trend in the carrier capture analysis from S-i-a-Si:H and MoOx layers.

Passivation of textured crystalline silicon with small pyramids by silicon nitride films formed by catalytic chemical vapor deposition and phosphorus catalytic impurity doping

Abstracts Silicon nitride (SiNx) films formed by catalytic chemical vapor deposition (Cat-CVD) and phosphorus (P) catalytic impurity doping (Cat-doping) are applied on textured crystalline silicon (c-Si) wafers with a pyramid size of 1–2 µm to reduce the surface recombination of minority carriers. SiNx single layer passivation realizes a surface recombination velocity (SRV) of less than 10 cm/s. The addition of a P Cat-doped layer results in a reduction in a SRV to ~7 cm/s owing to field-effect passivation. These values are comparable to those obtained in our previous study for textured c-Si surface with larger-sized pyramids, indicating the high passivation ability of Cat-CVD SiNx films and P Cat-doping independent of the size of pyramids. In addition to the double-side textured wafers, we also prepare a single-side textured wafer using Cat-CVD SiNx as an etching barrier. We find that Cat-CVD SiNx films can be utilized as an etching barrier against alkali solution, and a high effective minority carrier lifetime (τeff) of 2.3 ms has been obtained by the passivation with Cat-CVD SiNx films. These achievements will contribute to an improvement in the performance of back-contact c-Si solar cells.

Comparison of passivation properties of plasma-assisted ALD and APCVD deposited Al2O3 with SiNx capping

In this paper, we report on the direct comparison of Al2O3 films deposited by plasma-assisted atomic layer deposition (ALD) and atmospheric pressure chemical vapor deposition (APCVD) techniques on the passivation properties of both bare and boron diffused Si surfaces. It is found that ALD and APCVD deposited Al2O3 layers with SiNx capping have very similar chemical composition, hydrogen concentration at the Al2O3/Si interface, and interface defect density (Dit), but the ALD film has slightly higher negative fixed charge (Qf) after a high temperature (~750 °C) contact firing cycle typically used for solar cell fabrication. Both films showed excellent surface recombination velocities of <5 cm/s on planar and textured un-diffused Si wafers, but the ALD films gave 1 to 8 fA/cm2 lower emitter saturation current densities (J0e) on implanted boron emitters with sheet resistance in the range of 90–180 Ω/□. This is attributed to the observed slightly higher negative charge-induced field-effect passivation in the ALD films. However, SiNx/Al2O3/p+/n/n+ passivated emitter rear totally diffused (PERT) cell structures fabricated with 110 and 150 Ω/□ emitter in this study showed no appreciable difference in cell efficiency. Device analysis and simulations showed that even for >23% high-performance solar cells design, with very low bulk and rear contact recombination, the observed small difference in J0e has negligible effect on cell efficiency. Thus, APCVD Al2O3 passivation of B emitter can produce comparable efficiencies to their counterpart ALD Al2O3 passivated n-type Si solar cells.

Improved silicon oxide/polysilicon passivated contacts for high efficiency solar cells via optimized tunnel layer annealing

It is well known that the quality of contact passivation can greatly influence the efficiency of Si solar cells. In this work, the impact of annealing a wet-chemically formed silicon oxide (SiOx) tunnel layer (prior to poly-Si capping) to form SiOx/n+ poly-Si passivated contacts for high efficiency solar cells is investigated. The effect of different annealing temperatures (ranging from 425 to 900 °C) and ambients (air and forming gas), on the overall performance of the resulting SiOx/n+ poly-Si passivated contacts are studied. The efficiency potential of these SiOx/n+ poly-Si contacts is calculated from the measured values of the recombination current density (J0,contact), and the effective contact resistivity (ρcontact), according to the generalized Brendel's model. The results are compared to the reference case, i.e. non-annealed SiOx tunnel layer with poly-Si deposition. The lifetime, the fixed charge and also the SiOx tunnel layer thickness increase upon annealing at higher temperatures. The sample annealed in forming gas at 900 °C shows an increase in field effect passivation (Qtot = 1 × 1012 cm−2) as well as in chemical passivation (Dit = 3 × 1011 eV−1 cm−2), along with reduced ρcontact, indicating pinhole formation upon annealing at 900 °C. The best SiOx/n+ poly-Si passivated contact achieved J0,contact = 4.2 fA cm−2, ρcontact = 0.27 Ω cm−2 and a corresponding maximum ideal efficiency potential of 27.9%. This is 1.2% absolute higher as compared to the reference case, when no annealing of the tunnel layer is performed.