Minority Charge Carrier Lifetime Research Articles

Long-term carrier lifetime instabilities in n-type FZ- and Cz-silicon under illumination at elevated temperature

Even though n-type Si wafers show a lower extent of light-induced degradation, similar degradation and regeneration behavior as in p-type Si materials has been observed for various n-type Si monocrystalline materials. In this work, the long-term behavior of minority charge carrier lifetime in non-diffused n-type FZ-Si and Cz-Si wafers during illumination at elevated temperatures is investigated. Thereby, various influencing factors such as peak firing temperature and treatment temperature are considered. Degradation and a very strong regeneration effect, which exceeds the initial effective lifetime value, can be observed in the samples. Since surface-related saturation current density remains almost constant during degradation and regeneration, the effect seems to be bulk related. The extent of degradation and regeneration could be shown to be firing temperature-dependent. It could also be shown for n-type FZ-Si wafers that higher firing temperatures result in an increased H2 content within the silicon bulk. Investigations of the injection-dependent defect density revealed that the defect formed during degradation is not a deep level Shockley-Read-Hall defect. Observations at different treatment temperatures and constant illumination of 0.9(1) sun photon flux equivalent have shown that a higher treatment temperature leads to faster degradation and regeneration kinetics. Similarly, higher injection rates also speed up regeneration kinetics. Since degradation also occurs in darkness, the bulk related degradation effect in n-type FZ-Si is charge carrier-induced and not necessarily light-induced.

Recombination Activity of Crystal Defects in Epitaxially Grown Silicon Wafers for Highly Efficient Solar Cells

Aiming for highly efficient solar cells based on wafers with a low carbon footprint, silicon (Si) EpiWafers are grown epitaxially on reusable, highly doped Si substrates with a stack of porous Si layers (PorSi) for detachment. A state‐of‐the‐art p‐type Si EpiWafer exhibiting a minority charge carrier lifetime of up to 2.2 ms detected at an excess charge carrier density of ≈1 × 1015 cm−3 by photoluminescence (PL) imaging is presented. This translates to a predicted solar cell efficiency of 25.6%, calculated by efficiency limiting bulk recombination analysis (ELBA), and corresponds to losses of less than 1%abs compared to the theoretical limit of the investigated solar cell concept. A detailed loss analysis shows that the major remaining quality limitations are structural defects, specifically stacking faults (SFs). Therefore, the recombination activity of isolated SFs in epitaxially grown reference (EpiRef) wafers on polished substrates without a PorSi is assessed by highly resolved μPL mappings. The recombination activity rises with the number of dislocations within an SF as demonstrated by a comparison to microscope images. When using highly doped substrates, as currently required for EpiWafer fabrication, EpiRef wafers show more SFs exhibiting additionally a higher number of dislocations than SFs in EpiRef wafers on moderately doped substrates.

Optimizing inorganic SnS/ZrS2 heterojunction solar cells: Numerical analysis and performance insights

The SnS and ZrS2 have emerged as promising photovoltaic materials. This paper gives the first numerical analysis of inorganic SnS/ZrS2 heterojunction solar cells using SCAPS-1D. The study focuses on the effect of several parameters, such as thickness, doping charge carrier concentration, and energy bandgap, on fundamental solar cell properties in both the window and active layers. Our findings show that a variety of parameters influence solar cell performance, including built-in voltage, minority charge carrier lifetime, depletion breadth, charge carrier collection length, photogenerated current, and recombination rate. The maximum efficiency (η) attained in our simulated devices was 32.13 %, with FF of 84.51 % and Voc of 0.796 V. To achieve this efficiency, particular SnS parameters were used, such as a band gap of 1.00 eV, thickness of 5.0 μm, and doping charge carrier concentration of 1020 cm−3. In ZrS2, characteristics such as a band gap of 1.2 eV, thickness of 0.2 μm, and doping charge carrier content optimized 1020 cm−3 contribute to the observed efficiency. Our simulation results indicate that inorganic SnS/ZrS2 heterojunction devices have potential for solar device production that is cost-effective, large-scale, and high-efficiency. High performance enables a new path toward clean energy.

The effects of different anode manufacturing methods on deep levels in 4H-SiC p+n diodes

The manufacture of bipolar junctions is necessary in many 4H-SiC electronic devices, e.g., junction termination extensions and p+in diodes for voltage class >10 kV. However, the presence of electrically active levels in the drift layer that act as minority charge carrier lifetime killers, like the carbon vacancy (VC), undermines device performance. In the present study, we compared p+n diodes whose anodes have been manufactured by three different methods: by epitaxial growth, ion implantation, or plasma immersion ion implantation (PIII). The identification of the electrically active defects in the drift layers of these devices revealed that a substantial concentration of VC is present in the diodes with epitaxial grown or ion implanted anode. On the other hand, no presence of VC could be detected when the anode is formed by PIII and this is attributed to the effects of strain in the anode region. Our investigation shows that PIII can be a useful technique for the manufacture of bipolar devices with a reduced concentration of lifetime killer defects.

Investigation on the Long-Term Stability of AlOx/SiNy:H and SiNy:H Passivation Layers During Illuminated Annealing at Elevated Temperatures

Most crystalline Si based solar cells, e.g. passivated emitter and rear cells, rely on SiNy:H and AlOx/SiNy:H passivation layers. In this work, the long-term behavior of minority charge carrier lifetime in such symmetrically passivated samples during illuminated annealing at elevated temperatures is investigated by means of photoconductance decay based lifetime measurements, corona charging and capacitance voltage measurements. Thereby, AlOx layers, which are known to reduce H in-diffusion due to their barrier properties, deposited by atmospheric pressure chemical vapor deposition as well as by atomic layer deposition were considered enabling a comparison of different deposition techniques. The frequently published behavior of the bulk related degradation could be confirmed and the qualitative correlation between maximum defect density and the changing total amount of H in the Si bulk due to the barrier properties of the individual layers dielectric layers could be shown. Furthermore, for the subsequently observed degradation accelerated by a treatment at higher temperatures, literature indicates degradation to be caused by surface related degradation. Investigations on field effect passivation during degradation by means of corona charging and CV measurements showed a large drop in fixed negative charges in the passivation layer stacks.

Toward Highly Efficient Low‐Carbon Footprint Solar Cells: Impact of High‐Temperature Processing on Epitaxially Grown p‐Type Silicon Wafers

Conventional silicon (Si) wafers are produced by energy‐intensive ingot crystallization which is responsible for a major share of a solar cell's carbon footprint. This work explores Si epitaxially grown silicon wafers (EpiWafers) that are produced by direct epitaxial deposition of trichlorosilane on a reusable substrate. This approach requires less energy and material and hence offers a potential for reduced cost and carbon footprint. Solar cells made from EpiWafers usually suffer from efficiency losses due to recombination at structural crystal defects associated with epitaxial growth. The nature of these defects is investigated and defects at the EpiWafer's back surface are critical. Most of these defects are highly recombination‐active, pairwise‐connected misfit dislocations in the <110> direction. They originate from a lattice mismatch between the highly doped substrate and the less‐doped epitaxially grown layer. In this contribution, the detrimental impact of these defects can be mitigated using typical manufacturing processes of high‐efficiency solar cells, such as KOH etching, gettering, and oxidation. Local minority charge carrier lifetimes as high as 2.2 ms after industrially feasible processes are reported. Simulations using efficiency‐limiting bulk recombination analysis implies that the material would allow conversion efficiencies of up to 25.6% considering tunnel oxide‐passivated contact acting as rear emitter solar cell design.

Industrial Czochralski n‐type Silicon Wafers: Gettering Effectiveness and Possible Bulk Limiting Defects

An assessment of the bulk material quality of industrial Czochralski (Cz) grown phosphorus‐doped n‐type silicon (Si) wafers along an ingot is reported. The minority charge carrier lifetimes of the Cz‐Si wafer bulk before and after phosphorous (POCl3) diffusion gettering are assessed, by applying room‐temperature superacid surface passivation to avoid any additional gettering or hydrogenation effect. A substantial increase in the bulk lifetime of all of the n‐type Cz‐Si wafers along the ingot is observed, indicating the effectiveness of a gettering step for such wafers and the presence of getterable metallic impurities in these wafers. By experimentally monitoring the lifetime changes upon a gettering anneal and simulating the gettering kinetics based on different metal diffusivities, iron is identified to be a limiting defect, at least for the wafers from the tail part of the ingot. A dissolved iron concentration of is estimated from the bulk lifetimes of the tail wafers. This lifetime kinetics approach is also a demonstration of a new method to identify iron, or other getterable metals with moderate diffusivities such as chromium, in n‐type silicon wafers.

Optimising standard solar cell designs for maximum efficiency using genetic algorithms

ABSTRACT Solar energy is an alternative to conventional fossil fuels, and maximising the energy collected through solar cell design improvements is worthwhile. Genetic algorithms (GAs) have been historically useful in pursuing design improvements in solar cell architecture and manufacturing, particularly in combination with cell modelling software. This study demonstrates solar cell structural optimisation using PC3D software in combination with a genetic algorithm (GA) to maximise solar cell power conversion efficiency. PC3D is an Excel-based tool for modelling solar cells. The cell models examined here are: Passivated-Emitter Rear Contact (PERC), Interdigitated Back Contact (IBC), Aluminium-Back Surface Field (Al-BSF), and Passivated-Emitter Rear Locally Diffused (PERL). These are all silicon PV cells with varying structural features that significantly alter the performance of each cell. Absolute efficiency improvements of 2% for PERC, 1.6% for Al-BSF, 0.9% for IBC, and 0.5% for PERL cells are achieved. The main parameters impacting cell efficiency in this model are cell thickness and minority charge carrier lifetime, which feature a necessary trade-off between the higher absorption resulting from a thicker cell and the increased likelihood of charge collection arising from longer carrier lifetimes. These parameters are managed through other related values such as cell doping.

Increasing the Efficiency of Silicon Solar Elements by Doping with Nickel

It is shown that in the near-surface region of the solar cells (SCs) the concentration of nickel atoms is higher than in the bulk by 2–3 orders of magnitude, therefore, the gettering rate in the near-surface region is higher. Optimal modes of gettering by nickel clusters (i.e., nickel diffusion – Т = 800–850 °С, additional thermal annealing – Т = 750–800 °С) and the structure of a silicon SC were experimentally determined, which makes it possible to increase the efficiency of silicon SCs by 25–30% relative to the control. The physical mechanisms of the influence of the processes of diffusion of impurity nickel atoms and additional thermal annealing on the state of nickel atoms in the near-surface region and the SCs base and, accordingly, on the parameters of the SC are revealed. Physical models of the structure of a cluster of nickel atoms in silicon and the process of fast diffusing impurities gettering by clusters of nickel atoms are created. The binding energy of fast dissusing impurities atoms with a nickel cluster is estimated to be ~ 1.39 eV. The calculation shows that doping with nickel can increase the lifetime of minority charge carriers by 2–4 times, and the collection coefficient by 1.4–2 times. The experiment showed an increase in the minority charge carriers lifetime up to 2 times and an increase in efficiency by 25–30%.

Application of n‐Polysilicon Rear Emitter for High‐Efficiency p‐TOPCon Solar Cells

AbstractThis study entails the examination of tunnel oxide passivated contact on p‐type silicon wafers (p‐TOPCon) passivated with n‐polysilicon for a solar cell by using Quokka‐3, a numerical simulation program. The effects of the thickness, bulk lifetime, resistivity, and selectivity of charge carriers due to the polysilicon passivated contact are investigated. Through such n‐polysilicon passivated contact, the back‐emitter solar cells engender higher internal power owing to enhanced surface passivation. This further reduces the shading loss due to front metallization; however, the reduced minority carrier lifetime of the p‐type Czochralski (Cz) wafer restricts the possibilities for high efficiency. Subsequently, the minority charge carrier lifetime of the p‐type wafer conceivably becomes an obstacle to realizing TOPCon solar cells with a high conversion efficiency. This study demonstrates that a configuration suitable for the industrial manufacturing of high‐efficiency solar cells is a crystalline silicon solar cell on a p‐type wafer through a rear‐emitter n‐polysilicon passivated contact. A roadmap toward 24.87% of the p‐TOPCon solar cells through the n‐type polysilicon passivated contact is also devised.

Effect of nickel doping on the spectral sensitivity of silicon solar cells

In the modern industrial production of solar cells (SC), there is a growing trend to utilize “solar silicon” as the base material due to its cost-effectiveness. However, solar silicon possesses a drawback - it has a shorter lifetime of minority charge carriers (MCC), making it challenging to achieve high efficiency in solar cells. To address this limitation and improve the efficiency of solar cells based on “solar silicon,” two key objectives need to be met. Firstly, it is essential to increase the lifetime of photogenerated charge carriers. Secondly, there is a need to minimize both optical and electrical energy losses. To achieve an increase in the lifetime of minority charge carriers in SCs, a process called gettering can be employed. This process involves utilizing clusters of nickel atoms to trap uncontrolled impurity atoms. The paper presents the results of a study on the additional doping of silicon solar cells with nickel atoms, for factors affecting the long-wave and short-wave efficiency. Nickel doping has been shown to increase the efficiency of solar cells. It is determined that in the visible region of the spectrum the spectral sensitivity of a silicon solar cell doped with nickel is higher up to 25÷35% due to a decrease in surface recombination. Technological recommendations for nickel doping of single-crystal silicon solar cells are proposed to be combined without significant changes with the standard technological process for manufacturing solar cells.

IMPROVEMENT OF THE PASSIVATION PROPERTIES OF SiO<sub>2</sub> FILMS, GROWN BY THE METHOD OF RAPID THERMAL ANNEALING, AFTER CHEMICAL RCA TREATMENT

As it is known, increasing the efficiency of silicon solar cells is one of the most important tasks in modern alternative energy industry. Optimization of the antireflection and passivation layer is the most economical way to increase efficiency. In this work, the effect of pretreatment on the passivation properties of silicon dioxide (SiO 2 ) films grown by rapid thermal processing (RTP) at annealing temperatures of 900 and 950°C in a dry oxygen atmosphere, was studied. The growth of thin films of SiO 2 on the surface of monocrystalline silicon wafers was carried out in the AS-ONE 150 rapid thermal annealing chamber (France). Measurements of the lifetime of minority charge carriers by the non-contact microwave method showed that the best passivation of the samples is achieved by applying a preliminary three-stage chemical cleaning (RCA) of the surface of the n-type silicon wafers. IR spectroscopy confirmed the formation of a SiO 2 layer by the presence of an intense maximum at 1071 cm -1 , which was attributed to stretching vibrations of the "tensioncompression" type. The results of calculations of the optical constants of the obtained SiO 2 films using the reflection spectra and the SCOUT software show the presence of a silicon dioxide whose refractive index and extinction coefficient are close to the reference.

Laser ion source for semiconductor applications

Carbon implantation can be effectively used for axial minority charge carriers’ lifetime control in various silicon bulk and epitaxial planar structures. When carbon is implanted, more stable recombination centres are formed and silicon is not doped with additional impurities, as for example, when irradiated with protons or helium ions. Economically, such a process competes with alternative methods, and is more efficient for obtaining small lifetimes (several nanoseconds). I-3 ion injector with laser-plasma ion source at Institute for theoretical and experimental physics (ITEP) is used as ion implanter in semiconductors. The ion source uses pulsed CO2 laser setup with radiation-flux density of 1011 W/cm2 at target surface. The ion source produces beams of various ions from solid targets. The generated ion beam is accelerated in the two gap RF resonator at voltage of up to 2 MV per gap. Resulting beam energy is up to 4 MV per charge. Parameters of carbon ion beam generated and used for semiconductor samples irradiation during experiments for axial minority charge carriers lifetime control in various silicon bulk and epitaxial planar structures are presented.

Distribution of excess charge carriers in bilateral macroporous silicon with the same thickness of porous layers

In this work, to calculate the distribution of the excess minority carrier concentration in bilateral macroporous silicon, the solution of the diffusion equation for stationary conditions is used, which is written for a monocrystalline substrate and macroporous layers. The solution to the diffusion equation is supplemented by boundary conditions at the interface between macroporous layers and a monocrystalline substrate and at the boundaries of a bilateral macroporous silicon sample. The dependence of the distribution of the excess minority carrier concentration in bilateral macroporous silicon with the same thickness of porous layers on the depth of macropores, the thickness of the sample of bilateral macroporous silicon, and the bulk lifetime of minority charge carriers is calculated. It is shown that the distribution function of the excess minority carrier concentration in bilateral macroporous silicon exhibits two maxima. The maxima are located in the frontal macroporous layer, near the surface of the sample, and in a monocrystalline substrate, near the interface, the frontal macroporous layer - monocrystalline substrate.

Simulation of double-junction III-phosphides/silicon solar cells

The characteristics of two-junction solar cells were calculated in this work, in which phosphides of group III are used as the top junction, and Si as the bottom junction. The following ternary phosphide compounds Ga0.52In0.48P (1.85 eV), GaPN0.02 (1.9 eV), and GaPN0.04 (1.7 eV) were considered as the active material of the top junction. The use of GaPN0.04 allowed one to reach the current matching with the bottom Si junction and an efficiency of 30% was achieved. In addition, the influence of the layer thickness, the lifetime of minority charge carriers and the electronic affinity on the efficiency of solar energy conversion were considered.

Influence of minority charge carrier lifetime and concentration on crystalline silicon solar cells based on double antireflection coating: A simulation study

In this work, the optoelectrical properties of silver doped zinc oxide (Ag–ZnO)/ZnO double antireflection coating (ARC) layer were investigated by a simulation approach in terms of their minority charge carriers and surface charge carrier concentrations. From the experimental results, the Ag–ZnO/ZnO double ARC layer on Si solar cells presented the reduced average reflectance by 7.58% which was lowered to ZnO and Ag–ZnO single ARC layer. The simulation study demonstrated the reasonable electron and hole densities of 1.75 × 10 16 cm −3 and 1.51 × 10 16 cm −3 on c-Si solar cells with Ag–ZnO/ZnO double ARC layer. The simulated I–V characteristics evidenced that the performances of Ag–ZnO/ZnO double ARC layer-based Si solar cells gradually increased with the increase of the minority carrier lifetimes. As compared to a single ARC layer, the Ag–ZnO/ZnO double ARC layer-based Si solar cell achieved the highest conversion efficiency 14.32% with a fill factor of 81.35% at a minority carrier lifetime of 10 μs and carrier concentration of 1 × 10 17 cm −3 . The enhanced photovoltaic performance in Ag–ZnO/ZnO double ARC layer-based Si solar cells might be attributed to the high generation of electron-hole pairs, improved minority lifetime, and excellent carrier concentrations. • A simulation study was performed for optoelectrical properties of Ag–ZnO/ZnO double antireflection coating layer > Photovoltaic properties with respect to minority charge carriers/charge carrier concentrations studied > High electron and hole densities of 1.75 × 10 16 cm −3 and 1.51 × 10 16 cm −3 were observed > Ag–ZnO/ZnO double ARC layer based Si solar cell achieved the highest PCE 14.32%.

Extraordinarily High Minority Charge Carrier Lifetime Observed in Crystalline Silicon

Recent progress in surface passivation technology and wafer pretreatment already resulted in significant improvements in the achievable minority charge carrier lifetime of crystalline silicon. Herein, this is further exemplified by studying the lifetime on lowly doped crystalline silicon wafers passivated by poly‐Si. To ensure credible lifetime measurements multiple measurement techniques are compared and good agreement between the investigated approaches is found. The resulting lifetime curves are analyzed in detail and the main limitation is very likely caused by silicon bulk recombination—most likely due to impurities. This analysis indicates that even very low impurity concentrations can be a limiting factor at the extraordinary high level of charge carrier lifetime observed in this study. Despite these limitations, lifetimes of 0.18 s on p‐type and 0.5 s on n‐type crystalline silicon wafers are measured, which to our knowledge exceed previously reported lifetimes. In both cases, these measured lifetimes correspond to an effective minority charge carrier diffusion length of ≈2.5 cm.

Obtaining simultaneously high crystallinity and sub-bandgap absorption in femtosecond laser hyperdoped black silicon using ion beam etching

Femtosecond laser sulfur hyperdoped silicon (fs-hSi) is capable of absorbing photons in the infrared spectral range while simultaneously exhibiting negligible reflection. However, laser processing creates detrimental amorphous and polycrystalline silicon surface layers impairing electronic properties, especially reducing minority charge carrier lifetimes. This paper demonstrates how to selectively remove these disadvantageous layers by ion beam etching, while crystalline IR-absorbing silicon underneath is left. The increase in silicon crystallinity is quantified by laterally probing the fs-hSi samples with Raman spectroscopy.

Спектральні характеристики вихідних та опромінених світлодіодів GaAsP

The optical characteristics of the GaAs1-хPх output LEDs and LEDs irradiated with electrons with Е = 2 MeV, Ф = 1015 ÷ 1016 cm-2 were studied. The width of the band gap of the GaAs1-хPх (х = 0.45) solid solution was estimated. Its growth is caused by the heating of carriers by the field of the p-n junction. The damage coefficients of the lifetime of minority charge carriers for irradiated GaAsP LEDs have been calculated and the consequences of exposure to radiation on the operational parameter Т1, which determines the thermal stability of the diodes, have been analyzed.

Surface Passivation Studies of n-type Crystalline Silicon for HIT Solar Cells

Surface passivation of n-type Crystalline Silicon wafer using thin dielectric films is an important and major factor in improving photovoltaic performance of HIT solar cells. In this study, Numerical simulation was carried out by using AFORS-HET simulation software in which energy band diagram with and without surface passivation (a-Si:H(i)) was investigated and the highest conduction band offset obtained on n type c-Si wafer is 0.85 eV which is comparatively higher than p-type c-Si wafer which was reported between 0.1 and 0.15 eV. Performance of HIT solar cell with passivation layer is simulated and obtained efficiency of 12.9% by incorporating actual conditions to compare with experimentally obtained data. It has been understood that applying an effective dielectric passivation of silicon surface resulted with high open circuit voltage (Voc) and low surface recombination lead to an increase of cell efficiency by 1.1% (from 11.8 to 12.9%). Also, the simulated results shows that to obtain good conversion efficiency Defect density of interface (Dit) should be lower than 1x1011 cm−2eV−1. Validation of the simulation results is done by conducting PECVD experiments for optimizing the amorphous silicon passivation to a layer thickness down to 15 nm. HIT Solar cells have been developed, using the optimum layer of passivation, and their performance have been studied. An improvement in the minority charge carrier lifetime of ~53 µs (from 215 to 268 μs) and on the other hand reduction in the surface recombination velocity of ~ 12.9 cm/s (from 65.11 cm/s down to 52.23 cm/s) has been achieved through passivation which effectively increased the open circuit voltage (Voc) from 0.690 to 0.705 V. In this preliminary study, a conversion efficiency of 11.3% of heterojunction with intrinsic thin layer (HIT) solar cell on 10 mm × 10 mm n-c-Si wafer has been obtained.