Superior Passivation Research Articles

Ultra-thin Al2O3 capped with SiNx enabling implied open-circuit voltage reaching 720 mV on industrial p-type Cz c-Si wafers for passivated emitter and rear solar cells

In this study, we report on the passivation quality of atomic layer deposition grown ultra-thin Al2O3 and Al2O3 capped with plasma-enhanced chemical vapor deposition deposited SiNx on Cz p-type wafers for the rear side of a passivated emitter and rear cell (PERC). Different activation recipes using N2, forming gas (FG), and two-step annealing for different durations are investigated before SiNx deposition. The effect of different Al2O3 thicknesses and corresponding activation processes on the Al2O3/SiNx passivation performance, after a high temperature firing step, is studied to reach a new optimization toward higher efficiency and lower cost. A record high iVoc of 720 mV is obtained after firing step from Al2O3/SiNx stacks with Al2O3 thickness as thin as ∼2 nm with FG annealing. Our results demonstrate that, under well-optimized process conditions, ultra-thin Al2O3 thicknesses provide superior passivation quality as compared to the larger thicknesses which are commonly applied in the PERC industrial line and the potential for further improvement of industrial PERC solar cells in terms of cost reduction and efficiency.

Design of suppressing optical and recombination losses in ultrathin CuInGaSe2 solar cells by Voronoi nanocavity arrays

Cu(In, Ga)Se 2 (CIGS) solar cells have reached efficiencies over 23%. However, the scarcity of In and Se makes reducing the thickness of CIGS thin-film absorber desirable for mass production with low-cost and time-saving processes. Meanwhile, CIGS solar cells based on different architectures and strategies have drawn much attention for significant performance over conventional technologies, but rational design guidelines for optical and electrical performance optimization are yet to be completed. In this work, the reduced thickness of the CIGS thin film with the optical and electrical loss-passivated molybdenum Voronoi nanocavity arrays (VNCAs) electrodes were demonstrated. A structural-model under conformally coating criteria was investigated and optimized by a finite-difference time-domain method. The reduced parasitic absorption and rear surface recombination by Al 2 O 3 passivation layers on VNCAs substrates give rise to enhanced V OC and J SC up to 9.5 and 8.5%, respectively. These results confirm that the novel VNCAs electrodes can provide a cost-effective way for ultrathin CIGS solar cells with high efficiency. Design of suppressing optical and recombination losses in ultrathin CuInGaSe 2 solar cells by voronoi nanocavity arrays was demonstrated. The reduced parasitic absorption and rear surface recombination by Al 2 O 3 passivation layers on VNCAs substrates give rise to enhanced V OC and J SC up to 9.5 and 8.5 %, respectively. • The passivation of electrical and optical losses was achieved by a glancing angle deposition system. • The criteria of conformal coating is applied in the detailed optical modeling. • The effect of rear surface passivation was studied before and after post-selenization process. • The Al 2 O 3 layer shows superior passivation effects in electrical and optical losses.

A Ladder-like Dopant-free Hole-Transporting Polymer for Hysteresis-less High-Efficiency Perovskite Solar Cells with High Ambient Stability.

Perovskite solar cells (PSCs) have received high attention in the past few years due to their terrific photovoltaic performance and potentially low production cost. However, the use of hole transport materials (HTMs) with hygroscopic dopants, which cause the inevitable instability of device performance, has hampered commercialization. Herein, a dopant-free polymeric HTM with functional aromatic rings was used to optimize the HTM/perovskite interface and employed in a planar n-i-p configuration. Poly(1,4-(2,5-bis((2-butyloctyloxy)phenylene)-2,7-(5,5,10,10-tetrakis(4-hexylphenyl)-5,10-dihydro-s-indaceno[2,1-b:6,5-b']dithiophene)) (IDTB) co-polymer constructed with indaceno[1,2-b:5,6-b']dithiophene and bis(alkyloxy)benzene units adopts an S⋅⋅⋅O intramolecular bond linked ladder-like planar conjugated polymer backbone. Without any dopant, the hole mobility of IDTB is in the same order of magnitude as a doped 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (spiro-OMeTAD). Also, the hydrophobic nature of IDTB facilitated the long-term stability of the perovskite underneath. The unencapsulated PSC devices made of IDTB-based HTM achieved a power conversion efficiency of 19.38 % with a high moisture stability, retaining above 80 % of initial power conversion efficiency at 65 % relative humidity for more than 10 days. The superior passivation effect to perovskite surface made a hysteresis of 0.44 % was almost the least reported for regular planar undoped polymer HTM PSCs.

Electrochemical Behavior of Al–Al9Co2 Alloys in Sulfuric Acid

Al–Co alloys of various Co contents (2–20 wt.% Co) were fabricated by vacuum arc melting (VAM) with the scope to investigate the influence of cobalt on the microstructure and corrosion resistance of Al in 1 M H2SO4. The obtained microstructures were directional, consisting of Al9Co2 platelets (grown to coarse acicular plates as the Co content increased) uniformly dispersed in an Al-matrix. Alloying Al with Co did not decrease the rate of uniform corrosion of Al but it considerably increased its passivation ability. Moreover, all Al–Co alloys displayed lower uniform corrosion rate and notably higher passivation ability than market leading Al-alloys. The underlying mechanisms during anodic polarization in 1 M H2SO4 were identified and correlated with the microstructure. High Co content alloys (7–20 wt.% Co) presented superior passivation ability in 1 M H2SO4 as compared to the low Co content alloys.

Highly Efficient Silicon Nanowire Surface Passivation by Bismuth Nano-Coating for Multifunctional Bi@SiNWs Heterostructures.

A key requirement for the development of highly efficient silicon nanowires (SiNWs) for use in various kinds of cutting-edge applications is the outstanding passivation of their surfaces. In this vein, we report on a superior passivation of a SiNWs surface by bismuth nano-coating (BiNC) for the first time. A metal-assisted chemical etching technique was used to produce the SiNW arrays, while the BiNCs were anchored on the NWs through thermal evaporation. The systematic studies by Scanning Electron Microscopy (SEM), energy dispersive X-ray spectra (EDX), and Fourier Transform Infra-Red (FTIR) spectroscopies highlight the successful decoration of SiNWs by BiNC. The photoluminescence (PL) emission properties of the samples were studied in the visible and near-infrared (NIR) spectral range. Interestingly, nine-fold visible PL enhancement and NIR broadband emission were recorded for the Bi-modified SiNWs. To our best knowledge, this is the first observation of NIR luminescence from Bi-coated SiNWs (Bi@SiNWs), and thus sheds light on a new family of Bi-doped materials operating in the NIR and covering the important telecommunication wavelengths. Excellent anti-reflectance abilities of ~10% and 8% are observed for pure SiNWs and Bi@SiNWs, respectively, as compared to the Si wafer (50–90%). A large decrease in the recombination activities is also obtained from Bi@SiNWs heterostructures. The reasons behind the superior improvement of the Bi@SiNWs performance are discussed in detail. The findings demonstrate the effectiveness of Bi as a novel surface passivation coating, where Bi@SiNWs heterostructures are very promising and multifunctional for photovoltaics, optoelectronics, and telecommunications.

Aryl Diammonium Iodide Passivation for Efficient and Stable Hybrid Organ‐Inorganic Perovskite Solar Cells

AbstractSurface passivation is increasingly one of the most prominent strategies to promote the efficiency and stability of perovskite solar cells (PSCs). However, most passivation molecules hinder carrier extraction due to poorly conductive aggregation between perovskite surface and carrier transportation layer. Herein, a novel molecule: p‐phenyl dimethylammonium iodide (PDMAI) with ammonium group on both terminals is introduced, and its passivation effect is systematically investigated. It is found that PDMAI can mitigate defects at the surface and promote carrier extraction from perovskite to the hole transporting layer, leading to a lift of open‐circuit voltage of 40 mV. Profiting from superior PDMAI passivation, the average efficiency of PSCs has been elevated from 19.69% to 20.99%. As demonstrated with density functional theory calculations, PDMAI probably tends to anchor onto the perovskite surface with both NH3I tails, and enhances the adhesion and contact to perovskite layer. The exposed hydrophobic aryl core protects perovskite against detrimental environmental factors. In addition, the alkyl component between aryl and ammonium groups is demonstrated to be essentially vital in triggering passivation function, which offers the guidance for the design of passivation molecules.

25.11% efficiency silicon heterojunction solar cell with low deposition rate intrinsic amorphous silicon buffer layers

Here we report a certified efficiency of up to 25.11% for silicon heterojunction (SHJ) solar cells on a full size n-type M2 monocrystalline-silicon (c-Si) wafer (total area, 244.5 cm2). An ultra-thin intrinsic a-Si:H buffer layer was introduced on the c-Si wafer surface using a 13.56 MHz home-made RF-PECVD with low deposition rate showing superior surface passivation. The ultra-thin i-a-Si:H film with both higher microstructure factor (R*) and H content evidently increases the SHJ solar cell open-circuit voltage (VOC) by 2 mV, and moreover, short-circuit current (ISC) and fill factor (FF) are also notably improved, resulting in a 0.52% absolute cell efficiency enhancement, in which FF is the main cause. In order to explore high conversion efficiency SHJ solar cells, both home-made RF-PECVD and commercial VHF-PECVD (40.68 MHz) are employed for deposition of the i-a-Si:H passivation layer. As a result, the efficiency of RF-PECVD-prepared SHJ cell is 0.21% higher than that of VHF-PECVD-prepared, mainly driven by VOC and ISC boost. This work offers a useful tool for fabrication of high performance SHJ solar cells which could be employed in mass production.

Electrochemical behavior of TiN, CrN and TiN/CrN nanostructured coatings on the nickel-chromium alloy used in dental fixed prosthesis

ABSTRACT The aim of this research is the evaluation of the influence of TiN, CrN and TiN/CrN nanostructured coatings on corrosion resistance of nickel-chromium dental alloy in artificial saliva environment with two pH levels (3.0 and 6.5). Nickel-chromium alloy tested in this study were more resistant to corrosion in artificial saliva conditioning media when coated with different types of coating materials, as compared to uncoated alloy. The electrochemical measurements propose that the alloy with CrN coating has shown a high corrosion resistance in different pH levels. The superior passivation of CrN monolayer coating in modified Fusayama artificial saliva solution may be concluded from two essential factors, passive range, and corrosion current density. The passive range is well-developed, while the corrosion current density is much lower if compared to the other groups. Also, the Nyquist and polarization plots reveal that TiN, CrN and TiN/CrN nanostructured coatings have an excellent corrosion resistance which is considered much higher if compared to the substrate. The values of corrosion current density for CrN nanostructured coating in artificial saliva environment with two pH levels of 3.0 and 6.5 were 1.373 × 10−8 and 5.416 × 10−8 A.cm−2, respectively that were the lowest corrosion current density values among the other samples.

Numerical study of mono-crystalline silicon solar cells with passivated emitter and rear contact configuration for the efficiency beyond 24% based on mass production technology

Mono-crystalline silicon solar cells with a passivated emitter rear contact (PERC) configuration have attracted extensive attention from both industry and scientific communities. A record efficiency of 24.06% on p-type silicon wafer and mass production efficiency around 22% have been demonstrated, mainly due to its superior rear side passivation. In this work, the PERC solar cells with a p-type silicon wafer were numerically studied in terms of the surface passivation, quality of silicon wafer and metal electrodes. A rational way to achieve a 24% mass-production efficiency was proposed. Free energy loss analyses were adopted to address the loss sources with respect to the limit efficiency of 29%, which provides a guideline for the design and manufacture of a high-efficiency PERC solar cell.

Efficient Trap Passivation of MAPbI3 via Multifunctional Anchoring for High‐Performance and Stable Perovskite Solar Cells

AbstractChemical passivation of ionic defects in perovskite materials is an effective strategy to reduce charge recombination in perovskite solar cells (PSCs). Although several additives have been used for this purpose, the passivation mechanisms of different functional groups have remained unclear. Herein, the effect of molecules possessing multiple functional anchoring is systematically investigated. Three different multifunctional molecules namely 5‐aminoisophthalic acid (AIA), 5‐hydroxyisophthalic acid (HIA), and chelidamic acid (CA) are strategically chosen. These molecules not only take part in the crystallization process but also passivate the trap states effectively. CA shows superior passivation capacity among all with a better dipolar electron density distribution. The passivated films have considerably improved morphology with fewer pin holes, larger grains, and lower trap states in comparison to the pristine film. CA‐passivated p–i–n structured photovoltaic devices demonstrate the best power conversion efficiency (PCE) of 19.06% with an impressive open circuit voltage (VOC) of 1.097 V, whereas pristine devices show a PCE of 13.60% and VOC of 0.972 V. Moreover, the modified device reveals notable thermal and ambient stability in comparison to the pristine device due to lower defect states and reduced ion migration.

Cascaded band alignments of PbS heterojunction layers for improved performance of PbS quantum dot solar cells

Efficient energy band alignment of heterojunction layers in colloidal quantum dot (CQD)-based solar cells is a crucial factor to govern the charge transport characteristics and device performance. In this work, we develop novel cascaded-junctions of lead sulfide (PbS) CQD triple layers consisting of an alkylammonium iodide (AMI)-treated PbS bilayer and a 1,3-propanedithiol (PDT)-treated single layer. The two AMIs, i.e. triethylamine hydroiodide (tri-EAHI) and tetraethylammonium iodide (TEAI), are less hindered and have superior passivation performance compared to tetrabutylammonium iodide (TBAI), the most commonly used AMI. In addition, the band positions of the PbS-TEAI and PbS-tri-EAHI layers are deeper by 0.26 and 0.46 eV, respectively, than those of the PbS-PDT layer, and hence the sequential stacking of these three layers enable an effective cascaded band alignment. The various benefits of the improved band alignment such as increased built-in potential, reduced trap states, widened depletion region, enhanced charge transport and suppressed charge recombination lead to a significant improvement in the device parameters, and the best power conversion efficiency of 10.46% is obtained for the cascaded PbS-tri-EAHI/PbS-TEAI/PbS-PDT-based device.

Low-Temperature $p$-Type Microcrystalline Silicon as Carrier Selective Contact for Silicon Heterojunction Solar Cells

Silicon heterojunction (SHJ) solar cells have reached record efficiency, particularly in all-back contacted architectures. Despite this, two-side contacted SHJ cells still suffer from parasitic absorption and series resistance losses in the amorphous silicon contacts. An alternative to the doped amorphous silicon layer is microcrystalline silicon, which exhibits improved transparency and charge transport, while maintaining the superior passivation quality of all-silicon contact stacks. However, depositing thin, highly crystalline films has remained a challenge until recently. In this work, we use deposition temperatures $p$ -type $\mu$ c-Si:H contact layers. With these layers, we demonstrate $J_{\text{sc}}$ gains of 1 mA/cm $^2$ , while reducing series resistance below 1 $\Omega$ cm $^2$ , leading to screen printed 4 cm $^2$ cells with certified $\eta =\text{23.45}\%$ . Using a suite of device and material characterization techniques, we show that reduced deposition temperature leads to an increase in crystalline volume fraction from 35% to 55% for $p$ -type films, which mitigates parasitic absorption in the front contact and facilitates hole extraction. These improvements are explained as resulting from higher transparency in the $p$ -type layer accompanied by higher band bending in the c-Si wafer. These findings provide a method to improve SHJ solar cells performance, while offering insight into the importance of band bending considerations when optimizing heterojunction designs.

Direct observation of hydrogen at defects in multicrystalline silicon

AbstractHydrogen passivation is a key industrial technique used to reduce the recombination activity of defects in multicrystalline silicon (mc‐Si). However, not all dislocations and grain boundaries respond well to traditional hydrogen passivation techniques. In order to understand the reasons for these different behaviours, and how superior passivation might be achieved, a method is required for the direct observation of hydrogen at these defects. Here, we present a novel characterisation technique based on a combination of transmission Kikuchi diffraction (TKD), atom probe tomography (APT), and isotopic substitution that enables unambiguous detection and quantification of hydrogen atoms present at crystallographic defects in mc‐Si.

A Bifunctional Electrolyte Additive for High-Voltage LiNi0.5Mn1.5O4 Positive Electrodes.

4-(Trimethylsiloxy)-3-pentene-2-one (TMSPO) is tested as an electrolyte additive to enhance Coulombic efficiency and cycle retention for the Li/LiNi0.5Mn1.5O4 (LNMO) half-cell and graphite/LNMO full-cell. TMSPO carries two functional groups, siloxane (-Si-O-) and carbon-carbon (C═C) double bonds. It is found that the siloxane group reacts with hydrogen fluoride (HF), which is generated by hydrolysis of lithium hexafluorophosphate (LiPF6) by impure water in the electrolyte solution, to produce 4-hydroxypent-3-ene-2-one (HPO). The as-generated HPO, as well as TMSPO itself, is electrochemically oxidized to form a protective surface film on the LNMO electrode, in which it is inferred that the carbon-carbon (C═C) double bond initiates radical polymerization. The surface film derived from the TMSPO-added electrolyte shows a superior passivating ability to that generated from the pristine (TMSPO-free) electrolyte. The suppression of electrolyte oxidation enabled by the superior passivating ability offers two beneficial features to the half-cells and full-cells: the suppression of both HF generation and deposition of the resistive surface film on LNMO. As a result, the metal dissolution by HF attack on LNMO appears to be smaller by the addition of TMSPO. The cell polarization is also less significant because of the latter beneficial feature. In short, the bifunctional activity of TMSPO (HF scavenger and protective film former) allows an enhanced Coulombic efficiency and cycle retention to the half-cell and full-cell.

Enhanced irradiation and corrosion resistance of 316LN stainless steel with high densities of dislocations and twins

The irradiation and corrosion damages of nuclear materials have been a major challenge for the nuclear energy industry. Here, rotationally accelerated shot peening was used to improve the radiation and corrosion resistance of 316LN austenitic stainless steel by introducing high densities of dislocations and nanoscale twin boundaries. The dislocations and twins not only impeded the formation of helium bubbles and shear bands during irradiation, but also facilitated the formation of a superior passivation film, which significantly improved its corrosion performance. These observations provide an effective approach for designing irradiation- and corrosion-resistant nuclear materials.

Vanadium contamination on the stability of zeolite USY and efficient passivation by La2O3 for cracking of residue oil

It is of great significance to identify the destructive role of high deposited vanadium on the USY-based cracking catalysts and find a facile approach to vanadium passivation for processing residue oil. Herein, the destruction degree of the steam-treated vanadium-contaminated USY zeolites, which also contained a certain amount of Na ions, was investigated by N2 physical adsorption, NH3-TPD, HRTEM, 27Al MAS NMR and catalytic cracking evaluation. The results reveal that high deposited vanadium causes severe damage to the structure of USY, resulting in a sharp deterioration in cracking performance. Furthermore, CeO2 and La2O3 were studied as vanadium passivating agents. The introduction of La2O3 using physical mixing could preserve the zeolite structure to a large extent without altering the properties of USY. The superior passivation performance might be mainly attributed to the fact that La2O3 introduced by simple physical mixing prefers to interact with vanadium species, rather than migrate into the channels and cavities of zeolites USY.

Improved amorphous/crystalline silicon interface passivation for silicon heterojunction solar cells by hot-wire atomic hydrogen during doped a-Si:H deposition

Intrinsic/doped stacked hydrogenated amorphous silicon (a-Si:H) are widely used passivation layers for amorphous/crystalline silicon (a-Si/c-Si) heterojunction solar cells. This work reports that hot wire chemical vapor deposition of doped a-Si:H can significantly modify the property of the underlying intrinsic a-Si:H (a-Si:H(i)) as well as a-Si/c-Si interface passivation, which stems from the in-diffusion of highly reactive atomic hydrogen. Fourier transform infrared spectroscopy, spectroscopic ellipsometry and Raman analyses indicate that the underlying a-Si:H(i) films become more compact and less defected as a result of network reconstruction during doped a-Si:H capping. After this reconstruction, underdense a-Si:H(i) films obtained superior passivation quality than widely used dense layers, despite the inferior quality in the initial state. Effective minority carrier lifetime of c-Si passivated by underdense a-Si:H(i) was 19.9 ms, much higher than 15.2 ms in the case of using dense a-Si:H(i). The porous structure of underdense a-Si:H(i) facilitates hydrogen diffusion towards a-Si/c-Si interface and hence a rapid reduction of interface defect densities occurs, accounting for the better passivation quality. SHJ solar cells (160 μm, 156 × 156 mm2) with industry-compatible process were fabricated, yielding the efficiency up to 23.0% with high Voc values of 741 mV.

PbSe Quantum Dot Passivated Via Mixed Halide Perovskite Nanocrystals for Solar Cells With Over 9% Efficiency

PbSe quantum dots (QDs) have stronger electronic coupling resulting from a large Bohr exciton radius, suggesting PbSe QDs may be able to achieve superior charge separation and transport in optoelectronic devices compared with PbS QDs. However, PbS QDs solar cell have achieved a certified 12.01% power conversion efficiency (PCE), whereas PbSe QD photovoltaics lag behind at 8.2% PCE. One reason for this difference is that there has been significantly less work done on surface passivation of PbSe QDs. Here, the surface passivation of chlorinated PbSe QDs is optimized via a halide ion exchange treatment using mixed halide CsPb(Br/I)3 perovskite nanocrystals. Champion devices made from treated QDs achieved a PCE of 9.2%, Voc of 0.56 V, Jsc of 25.7 mA cm−2, and fill factor of 64%. Average PCEs for optimized cells are 8.9%. Detailed physical characterizations including capacitance‐voltage (C‐V), Voc, and Jsc as a function of light intensity, transient photovoltage, and photocurrent measurements are all carried out to investigate the mechanism of the improvement in the PCE and to understand the role of the mixed halide perovskites in providing superior surface passivation for PbSe solar cells. At this time, 9.2% is the highest PCE yet reported for PbSe QDs solar cells.

Dry Passivation Process for Silicon Heterojunction Solar Cells Using Hydrogen Plasma Treatment Followed by <italic>In Situ</italic> a-Si:H Deposition

A fully dry and hydrofluoric-free low-temperature process has been developed to passivate n-type crystalline silicon (c-Si) surfaces. Particularly, the use of a hydrogen (H2) plasma treatment followed by in situ intrinsic hydrogenated amorphous silicon (a-Si:H) deposition has been investigated. The impact of H2 gas flow rate and H2 plasma processing time on the a-Si:H/c-Si interface passivation quality is studied. Optimal H2 plasma processing conditions result in the best effective minority carrier lifetime of up to 2.5 ms at an injection level of 1 × 1015 cm−3, equivalent to the best effective surface recombination velocity of 4 cm/s. The reasons that enable such superior passivation quality are discussed in this paper based on the characterization of the a-Si:H/c-Si interface and c-Si substrate using transmission electron microscopy, high angle annular dark field scanning transmission electron microscopy, and deep-level transient spectroscopy.

Simple and versatile UV-ozone oxide for silicon solar cell applications

Semiconductor surface clean is sometimes perceived as costly but long recognized as pivotal in determining the final semiconductor device performance and yield. In this contribution, we investigated the effectiveness of crystalline silicon surface cleaning by a simple UV-ozone process in comparison to the industry standard RCA clean for silicon photovoltaic applications. We present a unique method of processing the silicon surface effectively by UV-ozone cleaning. Despite being simple, UV-ozone cleaning results in a superior surface passivation quality that is comparable to high-quality RCA clean. When used as a stack dielectric—UV-ozone oxide overlaid by aluminum oxide—the thickness of UV-ozone oxide plays an important role in determining the passivation quality. Of all treatment times, 15 min of UV-ozone treatment results in an outstanding passivation quality, achieving the effective carrier lifetime of 3 ms and saturation current density of 5 fA/cm2. In addition, we present a simple and effective technique to extract values of electron/hole capture cross-section for the purpose of analyzing the interface passivation quality from already measured surface recombination parameters of saturation current density, interfacial trap density and total fixed charge, instead of measuring on the separately prepared metal-insulated-semiconductor (MIS) samples by the techniques: frequency-dependent parallel conductance or deep-level transient spectroscopy.