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In p-type Czochralski-grown (Cz) silicon a light-induced degradation of the minoritycarrier lifetime is well known in the literature. Reducing the extent of this degradation would significantly improve the stable effective lifetime and thus the related performance of solar cells. In this work, the reduction of the density of the metastable defect underlying the degradation is performed by rapid thermal annealing (RTA). For a proper analysis it is extremely important to avoid contamination by the RTA furnace. Both, SiN[sub x] and SiO[sub 2] were examined as a barrier layer. A 60 nm SiN[sub x] layer was proven to act as the most effective barrier layer, allowing maintenance of a very high lifetime of 700 µs on 1·25 Ω cm p-type FZ material A design-of-experiments (DOE) study was used to analyze the effect of five process parameters on the stable effective lifetime. Especially, the plateau temperature shows a strong correlation with τ[sub d], the stable effective lifetime after light-induced degradation. The effect of plateau temperature on τ[sub d] of Cz- and FZ-Si wafers is examined in the temperature range of 700-1050°C for plateau time 120 s. It was found that the stable effective lifetime of all RTA-treated Cz-wafers is increased compared with the initial stable effective lifetime before processing. The highest increase of stable effective lifetime (by a factor of around 2) is obtained at 900°C with a process time of 120 s. This increase in lifetime is reflected in a reduced concentration of the metastable defect. [ABSTRACT FROM AUTHOR]

In order to utilize the full potential of solar cells fabricated on n-type silicon, it is necessary to achieve an excellent passivation on B-doped emitters. Experimental studies on test structures and theoretical considerations have shown that a negatively charged dielectric layer would be ideally suited for this purpose. Thus, in this work the negative-charge dielectric Al2O3 was applied as surface passivation layer on high-efficiency n-type silicon solar cells. With this front surface passivation layer, a confirmed conversion efficiency of 23.2% was achieved. For the open-circuit voltage Voc of 703.6 mV, the upper limit for the emitter saturation current density J0e, including the metalized area, has been evaluated to be 29 fA/cm2. This clearly shows that an excellent passivation of highly doped p-type c-Si can be obtained at the device level by applying Al2O3. [ABSTRACT FROM AUTHOR]

In the last years, novel materials for the formation of electron-selective contacts on n-type crystal-line silicon (c-Si) heterojunction solar cells were explored as an interfacial layer between the metal electrode and the c-Si wafer. Besides inorganic materials like transition metal oxides or alkali metal fluorides, also interfacial layers based on organic molecules with a permanent dipole moment are promising candidates to improve the contact properties. Here, the dipole effect plays an essential role in the modification of the interface and effective work function of the contact. The amino acids L-histidine, L-tryptophan, L-phenylalanine, glycine, and sarcosine, the nucleobase adenine, and the heterocycle 4-hydroxypyridine were investigated as dipole materials for an electron- selective contact on the back of p- and n-type c-Si with a metal electrode based on aluminum (Al). Furthermore, the effect of an added fluorosurfactant on the resulting contact properties was examined. The performance of n-type c-Si solar cells with a boron diffusion on the front was significantly increased when L-histidine and/or the fluorosurfactant was applied as a full-area back surface field. This improvement was attributed to the modification of the interface and the effective work function of the contact by the dipole material which was corroborated by numerical device simulations. For these solar cells, conversion efficiencies of 17.5% were obtained with open-circuit voltages (Voc) of 625 mV and fill factors of 76.3%, showing the potential of organic interface dipoles for silicon organic heterojunction solar cells due to their simple formation by solution processing and their low thermal budget requirements. [ABSTRACT FROM AUTHOR]

Off‐grid devices require autonomous power supply systems that can be achieved via coupling a solar cell with a supercapacitor in one integrated multifunctional device that is able to harvest energy from the environment, store, and release it on demand. Herein, a straight‐forward approach is proposed to realize a monolithic photosupercapacitor rechargeable under illumination by integrating a silicon (Si) solar cell with an electrochemical double‐layer capacitor (EDLC) based on mesoporous N‐doped carbon nanospheres (MPNC) in a three‐electrode configuration, i.e., via a shared electrode. The optimized porous structure of the MPNC‐EDLC electrodes results in a high storage efficiency of 95% and a superior performance compared to an activated carbon based EDLC. When monolithically integrated with a highly compatible and technologically robust Si solar cell in a photosupercapacitor, fast charging up to 0.63 V (2.5 V for a module of four photosupercapacitors connected in series) in less than 5 s is attained even under weak illumination conditions, with an outstanding peak overall efficiency of 11.8%. These results show high potential toward the development of photorechargeable and decentralized power sources for deployed smart electronic devices. [ABSTRACT FROM AUTHOR]

Passivating contacts based on thin tunneling Oxides (SiOx) and n- and p-type semi-crystalline or polycrystalline silicon (poly-Si) enable high passivation quality and low contact resistivity, but the integration of these p+/n emitter and n+/n back surface field junctions into interdigitated back contact silicon solar cells poses a challenge due to high recombination at the transition region from p-type to n-type poly-Si. Here, the transition region was created in different configurations--(a) p+ and n+ poly-Si regions are in direct contact with each other ("pn-junction"), using a local overcompensation (counterdoping) as a self-aligning process, (b) undoped (intrinsic) poly-Si remains between the p+ and n+ poly-Si regions ("pin-junction"), and (c) etched trenches separate the p+ and n+ poly-Si regions ("trench")--in order to investigate the recombination characteristics and the reverse breakdown behavior of these solar cells. Illumination- and injection-dependent quasi-steady state photoluminescence (suns-PL) and open-circuit voltage (suns-Voc) measurements revealed that non-ideal recombination in the space charge regions with high local ideality factors as well as recombination in shunted regions strongly limited the performance of solar cells without a trench. In contrast, solar cells with a trench allowed for open-circuit voltage (Voc) of 720?mV, fill factor of 79.6%, short-circuit current (Jsc) of 41.3?mA/cm², and a conversion efficiencies (η) of 23.7%, showing that a lowly conducting and highly passivating intermediate layer between the p+ and n+ poly-Si regions is mandatory. Independent of the configuration, no hysteresis was observed upon multiple stresses in reverse direction, indicating a controlled and homogeneously distributed breakdown, but with different breakdown characteristics. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The Metal Wrap Through+ (HIP-MWT+) solar cell is based on the PERC concept but features two additional electrical contacts, namely the Schottky contact between p-type Si bulk and Ag n-contact and the metal-insulator-semiconductor (MIS) contact on the rear side of the cell below the n-contact pads. To prevent thermal hotspots under reverse bias, both contacts shall either restrict current flow or allow a homogenous current flow at low voltage. In this work we present both options. First the stable reverse bias characteristics up to −15 V with a MIS contact using industrially manufactured SiON passivation and second, an integrated by-pass diode using AlOX as insulator in the passivation stack allowing current flows at approximately Vrev = –3.5 V depending on the chosen screen-print paste. The examined Schottky contacts break down at around Vrev = –2.5 V. Reverse bias testing of the cells reveals a solid performance of the cells under reverse bias and an average conversion efficiency of η = 21.2% (AlOX) and η = 20.7% (SiON), respectively. [ABSTRACT FROM AUTHOR]

Passivated contacts (poly-Si/SiOx/c-Si) doped by shallow ion implantation are an appealing technology for high efficiency silicon solar cells, especially for interdigitated back contact (IBC) solar cells where a masked ion implantation facilitates their fabrication. This paper presents a study on tunnel oxide passivated contacts formed by low-energy ion implantation into amorphous silicon (a-Si) layers and examines the influence of the ion species (P, B, or BF2), the ion implantation dose (5×1014cm-2 to 1×1016cm-2), and the subsequent high-temperature anneal (800 °C or 900 °C) on the passivation quality and junction characteristics using double-sided contacted silicon solar cells. Excellent passivation quality is achieved for n-type passivated contacts by P implantations into either intrinsic (undoped) or in-situ B-doped a-Si layers with implied open-circuit voltages (iVoc) of 725 and 720 mV, respectively. For p-type passivated contacts, BF2 implantations into intrinsic a-Si yield well passivated contacts and allow for iVoc of 690 mV, whereas implanted B gives poor passivation with iVoc of only 640 mV. While solar cells featuring in-situ B-doped selective hole contacts and selective electron contacts with P implanted into intrinsic a-Si layers achieved Voc of 690mV and fill factor (FF) of 79.1%, selective hole contacts realized by BF2 implantation into intrinsic a-Si suffer from drastically reduced FF which is caused by a non-Ohmic Schottky contact. Finally, implanting P into in-situ B-doped a-Si layers for the purpose of overcompensation (counterdoping) allowed for solar cells with Voc of 680mV and FF of 80.4%, providing a simplified and promising fabrication process for IBC solar cells featuring passivated contacts. [ABSTRACT FROM AUTHOR]

Thin layers of Al2O3 are well known for the excellent passivation of p-type c-Si surfaces including highly doped p+ emitters, due to a high density of fixed negative charges. Recent results indicate that Al2O3 can also provide a good passivation of certain phosphorus-diffused n+ c-Si surfaces. In this work, we studied the recombination at Al2O3 passivated n+ surfaces theoretically with device simulations and experimentally for Al2O3 deposited with atomic layer deposition. The simulation results indicate that there is a certain surface doping concentration, where the recombination is maximal due to depletion or weak inversion of the charge carriers at the c-Si/Al2O3 interface. This pronounced maximum was also observed experimentally for n+ surfaces passivated either with Al2O3 single layers or stacks of Al2O3 capped by SiNx, when activated with a low temperature anneal (425 °C). In contrast, for Al2O3/SiNx stacks activated with a short high-temperature firing process (800 °C) a significant lower surface recombination was observed for most n+ diffusion profiles without such a pronounced maximum. Based on experimentally determined interface properties and simulation results, we attribute this superior passivation quality after firing to a better chemical surface passivation, quantified by a lower interface defect density, in combination with a lower density of negative fixed charges. These experimental results reveal that Al2O3/SiNx stacks can provide not only excellent passivation on p+ surfaces but also on n+ surfaces for a wide range of surface doping concentrations when activated with short high-temperature treatments. [ABSTRACT FROM AUTHOR]

Over the past decade, the global cumulative installed photovoltaic (PV) capacity has grown exponentially, reaching 591 GW in 2019. Rapid progress was driven in large part by improvements in solar cell and module efficiencies, reduction in manufacturing costs and the realization of levelized costs of electricity that are now generally less than other energy sources and approaching similar costs with storage included. Given this success, it is a particularly fitting time to assess the state of the photovoltaics field and the technology milestones that must be achieved to maximize future impact and forward momentum. This roadmap outlines the critical areas of development in all of the major PV conversion technologies, advances needed to enable terawatt-scale PV installation, and cross-cutting topics on reliability, characterization, and applications. Each perspective provides a status update, summarizes the limiting immediate and long-term technical challenges and highlights breakthroughs that are needed to address them. In total, this roadmap is intended to guide researchers, funding agencies and industry in identifying the areas of development that will have the most impact on PV technology in the upcoming years. [ABSTRACT FROM AUTHOR]

This review explores the current state of the art in spatially resolved characterization of mixed‐halide perovskite solar cells. As the size of perovskite cells and modules continues to grow, quantification of the spatial distribution of key cell parameters will become increasingly valuable in predicting ultimate cell‐level performance and tracking process homogeneity. Here, both high resolution microscopic approaches using scanning techniques and camera‐based methods for full‐area cell and/or module analysis are discussed. The value of this local data in predicting performance losses at the cell level is particularly emphasized. Measurable physical parameters sensitive to losses of voltage, current, fill factor, and efficiency are discussed together with selected experimental results. It is demonstrated that a combination of spatially resolved cell parameter mapping/imaging can be used to quantitatively discriminate various loss contributions at high resolution. The impact and control of inhomogeneities become particularly important when upscaling from small devices to large formats compatible with industrial mass production. [ABSTRACT FROM AUTHOR]

The efficiency of photovoltaic energy conversion is a decisive factor for low-cost electricity from renewable energies. In recent years, the efficiency of crystalline silicon solar cells in mass production has increased annually by about 0.5–0.6%abs per year. In order to maintain this development speed, new technologies must be developed and transferred to industrial production. After the transition from full area Al back surface field cells to passivated emitter and rear contact cells, passivating contacts are an important step to get as close as possible to the efficiency limit of single junction Si solar cells. The theoretical background and the two prominent technologies for passivating contacts are presented and discussed. After implementing passivating contacts, the fundamental limit of single junction Si solar cells of 29.4% is in reach. Multi-junction solar cells are the most promising option to achieve efficiencies greater than 30%. Tandem technologies based on crystalline silicon as bottom cells have the advantage that they are based on a mature technology established on a gigawatt scale and can partially use the existing production capacity. In addition, silicon has an ideal bandgap for the lower subcell of a tandem solar cell. The two most promising material candidates for the top cell, i.e., III/V and perovskites, will be discussed. The presented technology routes show that silicon is able to maintain its outstanding position in photovoltaics in the coming years. [ABSTRACT FROM AUTHOR]

In this work, we analyse the light and elevated temperature induced degradation (LeTID) behaviour of gallium (Ga)-doped Czochralski (Cz) passivated emitter and rear cells (PERC). We show that these cells, based on industrial precursors, are prone to LeTID, degrading on average 8.3% rel in efficiency. The degradation and regeneration is slower than in boron (B)-doped PERC cells leading to a greater loss of energy over a 20 year lifespan of a solar module on a German rooftop, since, according to our experiments, regeneration does not start during that time frame. We show that the method of mitigating LeTID by slightly altering the temperature profile during fast firing, previously introduced on B-doped PERC cells, also works on Ga-doped PERC cells, reducing the maximum degradation to between 1% rel and 4% rel. This process does only slightly reduce the initial efficiency of the cell by up to 0.8% rel. Lastly, we show that increasing illumination and temperature from 0.15 suns eq. to 2 suns eq. and 75 °C to 140 °C, respectively, is an adequate way to accelerate LeTID testing on Ga-doped samples by more than two orders of magnitude while achieving qualitatively and quantitatively similar results to those obtained in a standard test. • Ga-doped PERC cells made from industrial precursors can show severe LeTID-degradation. • LeTID can be mitigated by adapting FFO firing profile. • This process can be implemented at relatively high belt speeds. [ABSTRACT FROM AUTHOR]

Light- and elevated temperature-induced degradation (LeTID), which can lead to significant module power loss in the field, has been extensively studied for boron (B)-doped silicon solar cells in the past. Current mass-production has shifted to gallium (Ga)-doped silicon substrates. Therefore, process influences on LeTID must be re-investigated for the changed acceptor species, as the LeTID-degradation extent and kinetics can be drastically different. We study the influence of the dielectric layer and the firing profile on the LeTID extent in Ga-doped lifetime samples. Furthermore, the effect of the bulk doping concentration is investigated. We find that a dielectric layer with high hydrogen content, a-SiN x :H (PECVD), leads to largest LeTID degradation. However, AlO x (PECVD) interlayers serve as very effective diffusion barriers, thus mitigating LeTID, as expected from studies on B-doped material. We observe no significant dependence of LeTID susceptibility on the doping concentration. Most interestingly, it appears that modifying the peak firing temperature, which has the greatest effect on the extent of LeTID in B-doped silicon, has a much smaller effect on the Ga-doped material, with LeTID being observed even when firing at 700 °C. • Ga-doped lifetime samples can show severe LeTID-degradation. • LeTID can be mitigated by adapting passivation layer and/or FFO firing profile. • Increasing temperature and illumination accelerates LeTID tests by a factor of 1000. [ABSTRACT FROM AUTHOR]

The excellent surface passivation of crystalline silicon provided by Al2O3 requires always an activation by a thermal post-deposition treatment. In this work, we present an indirect study of the reaction kinetics during such thermal activation treatments for Al2O3 synthesized by atomic layer deposition. The study was performed for Al2O3 deposited at varying temperatures, which results in different micro-structures of the films and, in particular, different hydrogen concentrations. The effective carrier lifetime was measured sequentially as a function of the annealing time and temperature. From these data, the reaction rate Ract and the activation energy EA were extracted. The results revealed a rather constant EA in the range of 1.4 to 1.5 eV, independent of the deposition temperature. The reaction rate, however, was found to increase with decreasing deposition temperature, which correlates with an increasing amount of hydrogen being incorporated in the Al2O3 films. This is a strong indication for an interface hydrogenation that takes place during the thermal activation, which is limited by the amount of hydrogen provided by the Al2O3 layer. [ABSTRACT FROM AUTHOR]

Multilayer stacks in the sequence c-Si/(Al 2 O 3 /SiO 2) n with n=1 (single multilayer stacks) or n=3 (triple multilayer stacks) with a thickness in the nanometer range were deposited to study their effects on silicon surface passivation and their charge dynamics compared to c-Si/Al 2 O 3 layer. It was revealed that field-effect passivation could be tuned by manipulating Q tot in the multilayer stacks by applying a voltage stress (V stress) of varying magnitude, duration and polarity. However, a degradation of τ eff after the application of high bias voltages is revealed which correlates with a strong increase of D it after the V stress application. [Display omitted] • Multilayers of c-Si/(Al 2 O 3 /SiO 2) n can modify material properties on nanometer scale. • Multilayers of c-Si/(Al 2 O 3 /SiO 2) n can modify material properties on nanometer scale. • High bias voltage degrades τ eff which correlate s with D it increase after V stress. Multilayer stacks in the sequence c-Si/(Al 2 O 3 /SiO 2) n with n = 1 (single multilayer stacks) or n = 3 (triple multilayer stacks) were deposited at different temperatures by plasma-enhanced atomic layer deposition (PEALD) with varying Al 2 O 3 thickness to investigate the formation of dipoles or trapped charges at the interfaces and their effect on the surface passivation quality. It was shown that the field-effect passivation deteriorated in multilayer stacks compared to an Al 2 O 3 single layer as flat-band voltage (V fb) and total amount of effective charges (Q tot) were lower than Al 2 O 3 reference layer (Al 2 O 3 single layer) (V fb = 2.36 V and Q tot = −1.13 × 1013 cm−3). However, choosing the right process conditions, the chemical passivation is comparable to the Al 2 O 3 reference layer. Multilayer stacks deposited at 250 °C with 3 nm of Al 2 O 3 interlayers exhibited a superior chemical passivation with effective lifetimes (τ eff) of 11 ms, characterized by a very low interface trap density (D it), which was comparable to the Al 2 O 3 reference layer. Furthermore, it was observed that field-effect passivation could be tuned by manipulating Q tot in the multilayer stacks by applying a voltage stress (V stress) of varying magnitude, duration and polarity (voltage of particular magnitude and sign applied for a specific time) before the capacitance–voltage measurement. The charge dynamics demonstrated that Q tot shifted from their original values under the effect of V stress which showed a high V fb shift (∼6.5 V), providing a gateway in tailoring the field-effect passivation quality of multilayer stacks on c-Si. Nevertheless, bias-photoconductance measurements reveal a degradation of τ eff after the application of high bias voltages which correlated with a strong increase of D it after the V stress application. [ABSTRACT FROM AUTHOR]

One drawback of passivating contacts in crystalline silicon solar cells is the current loss due to parasitic absorption within the involved material layers. When employed on an illuminated side of the cell, the full spectrum of the incident light will be partly absorbed before reaching the silicon bulk. Additionally, near-infrared (NIR) absorption can substantially reduce the cell's NIR spectral response (SR) also when employed on the non-illuminated side. As those losses are hard to measure directly, optical modeling is crucial for their quantification. This paper presents an extension to an analytical light-trapping model to account for parasitic absorption in the near-surface region via a new parameter A ppp (absorbed fraction per perpendicular pass). We test the model by analyzing i) reflectance measurements on samples with varying doping profiles, ii) SR measurements on TOPCon solar cells with varying back-side poly-silicon layers, and iii) SR measurements of a bifacial silicon heterojunction cell. We show that the model can well be calibrated by fitting a single value for A ppp to reflectance measurements. This enables a quantification of the parasitic absorption loss without requiring knowledge of all layer's optical properties. The model also is able to predict parasitic absorption in TOPCon cells when knowing the thickness and doping density of the poly-Si layer. Having proven the usefulness of A ppp to represent parasitic absorption as a single-valued quantity, we suggest A ppp as a third figure of merit for the quality of a passivating contact, next to the recombination parameter J 0c and the contact resistivity ρ c. • New parameter A ppp quantifies near-surface parasitic absorption in a c-Si solar cell. • A ppp extends an existing analytical light-trapping model. • Model can be fitted to reflectance to quantify parasitic absorption current loss. • Proposed as third figure of merit for a passivating contact besides J 0c and ρ c. [ABSTRACT FROM AUTHOR]

Abstract: 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) AlOx layers. Saturation current densities in the range of 5.2–38fAcm−2 (at 300K) were achieved on planar surfaces. In particular, we present an industrially relevant boron emitter, allowing for about 700mV open circuit voltage on textured surfaces, after a firing process. This high passivation quality could be achieved using AlOx passivation layers deposited by PECVD. The passivation quality is found to be equivalent to AlOx layers deposited by plasma-assisted atomic-layer-deposition. A wide range of surface doping concentration (2.5–70×1018 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. [Copyright &y& Elsevier]

In order to push silicon solar cell efficiencies further towards their limit, as well as to ensure accuracy of luminescence based characterization techniques, an accurate modeling of radiative recombination is important. It is well-known that the radiative recombination coefficient B rad of silicon shows a substantial charge carrier density dependence (c -dependence), often modelled via the scaling factor B rel quantified by Altermatt et al. Another effect lowering the total radiative recombination is photon recycling (PR), which depends mainly on the width and optical properties of the sample. PR also depends on free-carrier absorption (FCA), which introduces a further c -dependence. This work comprehensively reassesses and quantifies those influences on radiative recombination in silicon for photovoltaic (PV) applications. Firstly, it is evidenced that Altermatt's B rel model is dominated by the effect of band-gap narrowing (BGN). This clarifies that it should not be combined with a different BGN model to avoid modeling inconsistencies. It is thereby further confirmed that the band-to-band absorption coefficient of silicon does not show a relevant c -dependence for PV conditions. Next, a PR model is suggested which calculates a scaling factor B rel,PR. The model is proven useful in improving the interpretation of very high lifetime measurements. Finally, it is found that the c -dependence introduced by FCA affects the direct proportionality between luminescence signal and radiative recombination beyond charge carrier densities of 1016 cm−3 for samples thicker than typical wafer widths, and should then be considered in characterization techniques like e.g. calibrated lifetime measurements via photoluminescence. • Reviews common models and parameterizations for radiative recombination in silicon. • Charge carrier dependence is dominated by band-gap narrowing. • Altermatt's "Brel" model is a quantification of band-gap narrowing. • An analytical light-trapping model predicts photon recycling probability. • Photon recycling relevant for interpretation of very high lifetime measurements. [ABSTRACT FROM AUTHOR]

In this work, we present an approach to model metallization-induced recombination losses j 0,met of screen-printed fire-through metallization pastes, which are used e.g. for the contacts on the front side of passivated emitter and rear cells (PERC). Modelling is based on the local phosphorus emitter doping profile and the local microstructure of the interface between metal contact and silicon surface, which is characterized during a quantitative microstructural analysis using the scanning electron microscope (SEM). By comparing the modelled j 0,met to measured j 0,met results determined at the same position of both, the microstructural analysis and emitter doping profile, we find that in most cases recombination is dominated by the etch back of the emitter by the glass frit rather than by penetration of crystallites into the doped region. However, for crystallites protruding deep into the emitter or rather up to the junction, recombination at the crystallites becomes significant as well. Our modelled results yield indications that the etch depth into the emitter doping profile by the glass frit contained in the metallization paste, is sensitive to the emitter doping profile itself. • Metallization-induced recombination is dominated by the etch back of the emitter doping profile • Etch back of the emitter doping profile is sensitive to doping profile itself • Plating useful to enhance contrast for microstructure analysis [ABSTRACT FROM AUTHOR]

A vital part of poly-Si passivating contacts is the ultrathin interfacial oxide layer sandwiched between heavily-doped poly-Si and c-Si absorber that will herein be investigated in detail. The stoichiometry of differently prepared interfacial oxides in the as-grown state was investigated by XPS. The findings are correlated with the thermal stability of the oxide layers integrated in tunnel-oxide passivating contacts (TOPCon) which experience further structural modification during the high-temperature annealing step. More specifically, it was observed that a more stoichiometric interfacial oxide is a more effective diffusion barrier for dopants and, thereby enhanced the thermal stability of TOPCon structures with respect to the passivation quality. Furthermore, stoichiometric changes in the oxide layer upon subsequent contact formation (thermal annealing) were analyzed by XPS after selective etch back of the doped poly-Si layer. It is found that the interfacial oxide becomes more stoichiometric during annealing. In addition, a slight increase in oxide thickness was observed which tentatively could be explained by a large amount of unbound interstitial oxygen in the interface region. • Interfacial oxides in poly-Si based passivating contacts. • Stoichiometry of thermal interfacial oxides studied by XPS after oxidation and after high temperature annealing in TOPCon. • Thermal stability of interfacial oxide and TOPCon passivation quality. [ABSTRACT FROM AUTHOR]

Intense pulsed light (IPL) is capable of entirely replacing thermal annealing (curing and contact formation) within back end processing of silicon solar cells with passivating contacts. In order to demonstrate this, full-size silicon heterojunction (SHJ) cells with IPL-processed screen-printed metal contacts are fabricated. The device with the highest conversion efficiency reaches 23.0%, which is confirmed by Fraunhofer ISE CalLab. On average, IPL-annealed SHJ cells outperform their thermally treated pendants by 0.3–0.4% abs , in particular due to higher open-circuit voltages and fill factors. To further exploit the potential of IPL, it is applied to tunnel oxide passivating contacts (TOPCon). 2 cm × 2 cm-sized p -type solar cells with TOPCon layers on both sides are fabricated. On the front they exhibit indium tin oxide (ITO) layers as well as screen-printed metal contacts which are either thermally or IPL-annealed. The trade-off between low contact resistivity at the TOPCon/ITO interface and high-quality surface passivation (open-circuit voltages of up to 709.4 mV) is balanced, which is a current challenge for the optimization of such devices. The IPL-processed cells' series resistances do not differ significantly from those of thermally treated ones. Due to the pulse durations of several milliseconds only, IPL is very fast and offers a high throughput and, therefore, cost saving potential. • Full replacement of thermal annealing by intense pulsed light in back end processing of Si heterojunction solar cells, whereby conversion efficiency is increased and process time is reduced. • Presentation of the first intense-pulsed-light-annealed solar cells with tunnel oxide passivating contacts featuring screen-printed metal electrodes. • Understanding of intense-pulsed-light-induced electrical contact formation of screen-printed metal electrodes. [ABSTRACT FROM AUTHOR]

• Hybrid route for high band gap perovskite absorbers for tandem application. • Low-temperature n-i-p PSCs without use of toxic or reactive solvents. • Continuous band gap tuning shown by optical and structural analysis. • Investigation of co-evaporated inorganic scaffold and spin-coated solution. • Conformal high band gap perovskite thin film on µm-sized random pyramid textured silicon. Most efficient perovskite solar cells are synthesized by the one-step spin coating method. However, when applied on µm-sized textures, e.g. for efficient monolithic perovskite silicon tandems, no conformal film formation is achieved. In this respect, we investigate hybrid evaporation/ spin coating for mixed cation mixed halide perovskite absorbers [HC(NH 2) 2 0.83 Cs 0.17 Pb(I 1- x Br x) 3 (x = 0–0.28). By control of the 2nd deposition step, we demonstrate systematic band gap tuning from 1.54 to 1.75 eV. Moreover, critical criteria for synthesis and underlying charge transport materials (CTM) are determined by investigation of planar as well as scaffolded electron transport layers. Regarding the applicability on textures, the tandem-relevant 1.7 eV high band gap absorber is deposited on planar, pyramidal, and spiky black silicon to investigate crystallization and layer formation dependent on the substrate's topography. We recommend the presented hybrid method for realization of dense crystalline perovskite films with flat surface, deposition on planar CTM, and textured Si-based tandems with random pyramids. [ABSTRACT FROM AUTHOR]

Compositional engineering of organic-inorganic metal halide perovskite allows for improved optoelectrical properties, however, phase segregation occurs during crystal nucleation and limits perovskite solar cell device performance. Herein, we show that by applying tetrabutylammonium bistriflimide as an additive in the perovskite precursor solution, ultra-uniform perovskite crystals are obtained, which effectively increases device performance. As a result, power conversion efficiencies (PCEs) of 24.5% in a cell and 21.2% in a module are achieved, together with high stability under illumination, humidity and elevated thermal conditions., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

While perovskite photovoltaic (PV) devices are on the verge of commercialization, promising methods to recycle or remanufacture fully encapsulated perovskite solar cells (PSCs) and modules are still missing. Through a detailed life-cycle assessment shown in this work, we identify that the majority of the greenhouse gas emissions can be reduced by re-using the glass substrate and parts of the PV cells. Based on these analytical findings, we develop a novel thermally assisted mechanochemical approach to remove the encapsulants, the electrode, and the perovskite absorber, allowing reuse of most of the device constituents for remanufacturing PSCs, which recovered nearly 90% of their initial performance. Notably, this is the first experimental demonstration of remanufacturing PSCs with an encapsulant and an edge-seal, which are necessary for commercial perovskite solar modules. This approach distinguishes itself from the "traditional" recycling methods previously demonstrated in perovskite literature by allowing direct reuse of bulk materials with high environmental impact. Thus, such a remanufacturing strategy becomes even more favorable than recycling, and it allows us to save up to 33% of the module's global warming potential. Remarkably, this process most likely can be universally applied to other PSC architectures, particularly n-i-p-based architectures that rely on inorganic metal oxide layers deposited on glass substrates. Finally, we demonstrate that the CO 2 -footprint of these remanufactured devices can become less than 30 g/kWh, which is the value for state-of-the-art c-Si PV modules, and can even reach 15 g/kWh assuming a similar lifetime., Competing Interests: The authors declare the following competing financial interest(s): P.v.W. is an employee of Energy21 BV, D.Ma., S.N. and A.V. are employees of Solaronix SA, S.S. is a co-founder of Swift Solar., (© 2024 The Authors. Published by American Chemical Society.)

The efficiency of perovskite/silicon tandem solar cells has exceeded the previous record for III-V-based dual-junction solar cells. This shows the high potential of perovskite solar cells in multi-junction applications. Perovskite/perovskite/silicon triple-junction solar cells are now the next step to achieve efficient and low-cost multi-junction solar cells with an efficiency potential even higher than that for dual-junction solar cells. Here we present a perovskite/perovskite/silicon triple-junction solar cell with an open circuit voltage of >2.8 V, which is the record value reported for this structure so far. This is achieved through employing a gas quenching method for deposition of the top perovskite layer as well as optimization of interlayers between perovskite subcells. Moreover, for the measurement of our triple-junction solar cells, precise measurement procedures are implemented to ensure the reliability and accuracy of the reported values., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

A resist-free metallization of copper-plated contacts is attractive to replace screen-printed silver contacts and is demonstrated on large-area silicon heterojunction (SHJ) solar cells. In our approach, a self-passivated Al layer is used as a mask during the plating process. In this study, Al/AlO x or Al 2 O 3 plating masks are further functionalized by a self-assembled monolayer (SAM) of octadecyl phosphonic acid (ODPA). The ODPA adsorption is characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy in attenuated total reflectance (FTIR-ATR) (in situ), and contact angle measurements to link the surface chemical composition to wetting properties. The SAM leads to homogeneous hydrophobic surfaces on large-area textured solar cells and planar flexible printed circuit boards (PCBs), which allows reproducible patterning of narrow lines by inkjet printing of an etchant. Selective copper plating is then performed to complete the metallization process and produce Cu contacts in the patterned areas. Silicon heterojunction (SHJ) solar cells metallized by the complete sequence reached up to 22.4% efficiency on a large area.

Measuring the surface temperature of objects that are processed in conveyor belt furnaces is an important tool in process control and quality assurance. Currently, the surface temperature of objects processed in conveyor belt furnaces is typically measured via thermocouples. However, infrared (IR) thermography presents multiple advantages compared to thermocouple measurements, as it is a contactless, real-time, and spatially resolved method. Here, as a representative proof-of-concept example, an inline thermography system is successfully installed into an IR lamp powered solar firing furnace, which is used for the contact firing process of industrial Si solar cells. This protocol describes how to install an IR camera into a conveyor belt furnace, conduct a customer correction of a factory calibrated IR camera, and perform the evaluation of spatial surface temperature distribution on a target object.

We present a process development leading to efficient rear side light trapping structures with the purpose of enhancing the infrared response of a silicon-based tandem solar cell. To this end, we make use of phase separation effects of two immiscible polymers, polystyrene and poly(methyl methacrylate), resulting in a non-periodic polystyrene structure on silicon with a well-defined size distribution. Onto this pattern, we evaporate silver as a scattering rear side mirror and contact layer. Average feature sizes and periods can be tuned by varying material properties (e.g. molar weights or ratios of the polymers) as well as processing conditions during the spin coating. This way a favorable pseudo period of approx. 1 µm for these disordered structure features was realized and successfully implemented into a silicon solar cell. The structure shows a ring-shaped scattering distribution which is beneficial for light trapping in solar cells. External quantum efficiency measurements show that a gain in short circuit current density of 1.1 mA/cm 2 compared to a planar reference can be achieved, which is in the same range as we achieved using nanoimprint lithography in a record triple-junction III/V on a silicon device.

Homogeneous layer formation on textured silicon substrates is essential for the fabrication of highly efficient monolithic perovskite silicon tandem solar cells. From all well-known techniques for the fabrication of perovskite solar cells (PSCs), the evaporation method offers the highest degree of freedom for layer-by-layer deposition independent of the substrate's roughness or texturing. Hole-transporting polymers with high hole mobility and structural stability have been used as effective hole-transporting materials (HTMs) of PSCs. However, the strong intermolecular interactions of the polymers do not allow for a layer formation via the evaporation method, which is a big challenge for the perovskite community. Herein, we first applied a hole-transporting terthiophene polymer (PTTh) as an HTM for evaporated PSCs via an in situ vapor-phase polymerization using iodine (I 2 ) as a sublimable oxidative agent. PTTh showed high hole mobility of 1.2 × 10 -3 cm 2 /(V s) and appropriate energy levels as HTM in PSCs ( E HOMO = -5.3 eV and E LUMO = -3.3 eV). The PSCs with the in situ vapor-phase polymerized PTTh hole-transporting layer and a co-evaporated perovskite layer exhibited a photovoltaic conversion efficiency of 5.9%, as a proof of concept, and high cell stability over time. Additionally, the polymer layer could fully cover the pyramidal structure of textured silicon substrates and was identified as an effective hole-transporting material for perovskite silicon tandem solar cells by optical simulation.

Perovskite silicon tandem solar cells have the potential to overcome the efficiency limit of single-junction solar cells. For both monolithic and mechanically stacked tandem devices, a semi-transparent perovskite top solar cell, including a transparent contact, is required. Usually, this contact consists of a metal oxide buffer layer and a sputtered transparent conductive oxide. In this work, semi-transparent perovskite solar cells in the regular n-i-p structure are presented with tin-doped indium oxide (ITO) directly sputtered on the hole conducting material Spiro-OMeTAD. ITO process parameters such as sputter power, temperature, and pressure in the chamber are systematically varied. While a low temperature of 50 °C is crucial for good device performance, a low sputter power has only a slight effect, and an increased chamber pressure has no influence on device performance. For the 5 × 5 mm 2 perovskite cell with a planar front side, a 105 nm thick ITO layer with a sheet resistance of 44 Ω sq -1 allowing for the omission of grid fingers and a MgF 2 antireflection coating are used to improve transmission into the solar cells. The best device achieved an efficiency of 14.8%, which would result in 24.2% in a four-terminal tandem configuration.