Dark Saturation Current Density Research Articles

34.151 % (33.93 %) - Maximal Efficiencies investigated in New n+(p+) - p(n) CdTe1-xSx, CdTe1-xSex - Crystalline Alloy Junction Solar Cells at 300 K, According to Highest Hot Reservoir Temperatures

In two new single n+(p+)−p(n) X(x)-alloy junction solar cells at 300 K, [X(x)≡CdTe1−xSx, CdTe1−xSex],0≤x≤1, by basing on the same physical model-and-treatment method, as used in our recent works [1, 2], and also other works [3-11], some important results, obtained in the present work, are reported in the following.As noted in Tables 2.1, 3.1, 4.1 and 5.1, the dark carrier-minority saturation current density

Enhanced Spectral Response of ZnO-Nanorod-Array-Based Ultraviolet Photodetectors by Alloying Non-Isovalent Cu-O with CuAlO2 P-Type Layer.

CuAlO2 was synthesized by a hydrothermal method, in which the Cu-O dimers were incorporated by simply altering the ratio of the reactants and the temperature. The incorporation process increases the grain size in CuAlO2, and modulates the work function and binding energies for CuAlO2 due to the partial substitution of Cu+ 3d10 with Cu2+ 3d9 orbitals in the valence band maximum by alloying non-isovalent Cu-O with a CuAlO2 host. Based on the ZnO nanorod arrays (NRs) ultraviolet photodetector, CuAlO2/Cu-O fabricated by the low-cost drop-coating method was used as the p-type hole transport layer. The incorporation of the Cu-O clusters into CuAlO2 lattice to enhance the conductivity of CuAlO2 is an effective way for improving ZnO NRs/CuAlO2 device performance. The photodetectors exhibit significant diode behavior, with a rectification ratio approaching 30 at ±1 V, and a dark saturation current density 0.81 mA cm-2. The responsivity of the ZnO-NRs-based UV photodetector increases from 13.2 to 91.3 mA/W at 0 V bias, with an increase in the detectivity from 2.35 × 1010 to 1.71 × 1011 Jones. Furthermore, the ZnO NRs/[CuAlO2/Cu-O] photodetector exhibits a maximum responsivity of 5002 mA/W at 1.5 V bias under 375 nm UV illumination.

Stack Diffusion Process for Cost- and Energy-Efficient Boron Emitter Formation

The boron emitter formation for tunnel oxide passivated contact (TOPCon) solar cells faces higher costs compared to the POCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> diffusion for passivated emitter and rear (PERC) solar cells due to the requirement for higher temperatures and longer process times. This work presents an alternative energy-efficient and low cost of ownership boron diffusion approach for TOPCon solar cells, enabling a highly increased throughput compared to the typically used gas phase diffusion. We use an atmospheric pressure chemical vapor deposition borosilicate glass layer as the boron dopant source and combine it with a subsequent thermal anneal in a quartz tube furnace for dopant drive-in. Here, we either use a conventional single-slot quartz boat configuration, or, for highly increased throughput, a vertical wafer stack configuration with the wafer surfaces in direct contact with each other. We show that this approach yields an emitter doping profile comparable to the state-of-the-art gas phase diffusion with sufficient uniformity across the wafer area. We further investigate the emitter dark saturation current densities <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0e</sub> as well as the energy conversion efficiency of TOPCon solar cells fabricated for each configuration and compare the results to those of a BBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> reference process. These solar cells achieve energy conversion efficiencies exceeding 23% for the stack diffusion approach. Additionally, we demonstrate a potential reduction in both the cost of ownership and the specific electricity consumption of the presented approach.

Inline-Feasible Contrast Separation in Luminescence Imaging for Silicon Solar Cells

We present an article about separating contrasts in luminescence images of silicon solar cells for industrial application, i.e., in very short measurement times significantly below one second. The well-known method “Coupled Determination of Dark Saturation Current Density and Series Resistance” by Glatthaar <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> is optimized to drastically decrease the required exposure time. The correction using an image under short-circuit conditions is omitted. Simulations with Quokka3, which give insight into the mechanisms of contrast separation, are performed. The operating points at which the images are acquired are adjusted allowing short data acquisition times. The optimized method decreases the necessary exposure time by more than a factor of 6 to 160 ms for a multicrystalline silicon passivated emitter and rear cell (PERC) solar cell. The quality regarding contrast separation can be maintained.

Heterojunction between crystalline silicon and nanocomposite coupled ZnO·SnO2 and optimization of its photovoltaic performance

In this work coupled ZnO·SnO2 nanocomposite has been used as heterojunction partner to Si for photovoltaic application and its performance is optimized. The interface defect more than 1012 cm−2 reduces the short circuit current density, fill factor and efficiency of the device. In addition, the best device performance is observed at the vicinity of 280K. The junction of the device has a dark saturation current density and ideality factor of the order of 10−4 Acm−2 and 21 respectively. In addition, four different organic materials are used as back surface field layer (BSL) to the same device and performance is improved. The best conversion efficiency and open circuit voltage as high as 4.1% and 0.591 V respectively are obtained for the device with CuSCN as BSL. Consequently, a range of combined values of the energy band gap and electron affinity of the BSL materials are examined for optimal device performance.

Investigating the degradation behaviours of n+-doped Poly-Si passivation layers: An outlook on long-term stability and accelerated recovery

In this article, we study the kinetics of firing-activated degradation and recovery of industrially processed n + -doped poly-Si on thin oxide passivation layers subjected to illuminated annealing at elevated temperatures. The impact of a comprehensive range of fast-firing conditions on the subsequent degradation and recovery were assessed. The results indicate that the recovery process is dependent on the peak firing temperature, where higher temperatures led to an improvement in effective lifetime of up to 20% compared to the pre-fired state, and a very low surface dark saturation current density of 2.9 fA/cm 2 . By cycling through light soaking and dark anneal conditions, we show that unlike the commonly studied boron-oxygen light-induced degradation (BO-LID) and light- and elevated temperature-induced degradation (LeTID), this newly observed instability in n + -doped poly-Si passivation layers is not reversible, that is, once a degradation/recovery cycle is completed, the lifetime remains very stable under subsequent light soaking. This indicates that the surface related instability may be able to be completely resolved following the completion of the first degradation/recovery cycle. With this in mind, we investigate the potential for high intensity laser illumination (up to 150 kW/m 2 ) to rapidly increase the recovery rates, however, this does not seem sufficient to cycle through degradation and recovery on a timescale that is amenable with mass production. The mitigation of any potential instabilities at the poly-Si interface has significant implications for the reliability of n-type tunneling oxide passivated contact (TOPCon) solar cells. • Firing conditions have a significant impact in stability of polysilicon passivation. • The firing-induced surface instability is different to previous degradation modes. • Cycling between degraded and recovered states does not occur.

Industrial High Throughput Emitter Formation and Thermal Oxidation for Silicon Solar Cells by the High Temperature Stack Oxidation Approach

Herein, the high temperature stack oxidation (HiTSOx) approach for the fabrication of passivated emitter and rear cells (PERCs) is investigated. This approach features a combination of phosphorus oxychloride (POCl3) diffusion shortened to the phosphosilicate glass (PSG) deposition phase as well as high temperature thermal oxidation using stacked wafers. During the latter thermal oxidation, the incorporated phosphorus is redistributed and diffuses deeper into the silicon wafer. The simultaneously growing thermal dioxide serves as a passivation layer. Due to the use of stacked wafers, the throughput of the HiTSOx approach is three times higher in comparison to state‐of‐the‐art oxidation at moderate temperature. Applying a busbarless metallization layout, a median energy conversion efficiency of η = 22.2% is achieved for the HiTSOx approach, being similar to the performance of the reference group with state‐of‐the‐art PERC processing also with η = 22.2%. Despite stacking of the wafers during the thermal oxidation, an excellent homogeneity of the oxide layer thickness of ±1 nm over the wafer surface is found, whereas the passivation quality features dark saturation current densities j0e as low as j0e = (30 ± 3) fA cm−2 at emitter sheet resistances Rsh = (199 ± 6) Ω sq−1.

Interfacial engineering of a thiophene-based 2D/3D perovskite heterojunction for efficient and stable inverted wide-bandgap perovskite solar cells

Fabricating highly efficient and stable inverted wide-bandgap (WBG) perovskite solar cells (PSCs) is the key factor for developing high-efficiency and stabilized tandem solar cells. Herein, we propose an interfacial engineering strategy to form a 2D/3D perovskite heterojunction using 2-thiopheneethylammonium chloride (TEACl). The thiophene-based 2D/3D perovskite heterojunction improves the optoelectronic properties of the perovskite absorber, passivates the electron and hole traps, increases the activation energy of the ion movement, and lowers the dark saturation current density of the device. As a result, the device with TEACl treatment delivers a champion power conversion efficiency of 20.31% with a 1.68-eV bandgap. In addition, the devices with TEACl treatment exhibit superior stability than the control devices under various testing conditions. Finally, an efficiency of 24.0% is achieved for a 4-terminal perovskite/CIGS tandem solar cell. Our results demonstrate that the thiophene-based 2D/3D perovskite heterojunction is a promising approach for achieving efficient and stable WBG PSCs.

Revised parametrization of the recombination velocity at SiO2/SiNx-passivated phosphorus-diffused surfaces

We investigate the effective surface recombination velocity Seff of alkaline textured, Phosphorus-diffused and thermal SiO2/SiNx passivated surfaces with an emphasis on the impact of the thermal oxidation temperature. The application of a recent calibration procedure for the carrier lifetime measurements enables a precise determination of the dark saturation current density. The experimental results include 25 diffusion/oxidation process combinations that cover a wide range of final surface concentration levels Ns between 3⋅1020 cm−3 and 1⋅1019 cm−3, using oxidation temperatures Tox from 650 °C to 900 °C. This yields a data set that enables a revision of the commonly applied parameterization of the effective surface recombination velocity of this passivation scheme using numerical simulation. In addition, the impact of fixed surface charges is modeled for separating field effect and chemical passivation properties. Also, the role of the oxidation temperature on the passivation quality is investigated.

Impact of boron doping on electrical performance and efficiency of n-TOPCon solar cell

A big challenge to improve the conversion efficiency of n-type solar cell is the recombination and electrical contacting of boron (B)-doped emitters in n-TOPCon solar cells. This work investigates the emitter dark saturation current density under the passivation layer (J0e, passivated), the metallization-induced recombination current density under the metal contact (J0e, metal), and the I–V parameters, including short-circuit current density (Jsc), open circuit voltage (Voc), fill factor (FF) and efficiency (Eff) as functions of the peak concentration (Nmax) and junction depth of B-doped profile. We introduced the profile with the peak concentration of 1–1.5 × 1019 atoms/cm3 and a junction depth of 0.75–1.0 μm to improve the conversion efficiency of 23.4%. The results revealed that Jsc, implied Voc (iVoc) and the contact resistance (ρc) were negative correlated with the Nmax and junction depth. However, J0e, passivated had a positive correlation with the same. The results from ρc, J0e along with the I–V showed the junction depth of emitter doping profiles need to exceed the corroded depth of Ag/Al paste to get a low ρc, meanwhile, a low J0e should be ensured. The results suggested theB-selective emitters were developed with a low ρc and a low J0e. After optimizing B-selective emitters and passivation processes, we obtained industry-grade TOPCon cells with Eff, Voc, Jsc, and FF as high as 23.7%, 709 mV, 40.8 mA/cm2, and 82%, respectively. This optimized B-doped and simplified B-selective emitters processes can be commercially applied in photovoltaics.

Low Recombination Firing-Through Al Paste for N-Type Solar Cell with Boron Emitter

A kind of low recombination firing-through screen-printing aluminum (Al) paste is proposed in this work to be used for a boron-diffused N-type solar cell front side metallization. A front side fire-through contact (FTC) approach has been carried out for the formation of local contacts for a front surface passivated solar cell. With a low contact resistivity (ρc) of 1.0 mΩ·cm2, good ohmic contact between the boron-doped front surface of the silicon sample and the Al paste was realized. To obtain a good energy conversion efficiency, a balance can be achieved between the open circuit voltage (Voc) and contact resistivity (ρc) of the cell by combining suitable Al powders and appropriate additives. The detailed micro-contact difference in Si/metallization between the firing-through Al paste and silver-aluminum (Ag-Al) paste was analyzed. The dark saturation current density beneath the metal contact (J0, metal) of the Si/metallization region using our firing-through Al paste was discussed, which was proven to be 61% lower than using Ag-Al paste. The pseudo energy conversion efficiency of the cell using Al paste measured by Suns-VOC was also higher than using Ag-Al paste. The role of Al paste in low surface metal recombination is discussed. The utilization of this new kind of Al paste was much cheaper and more convenient, compared to the traditional process using Ag or Ag-Al paste.

Advanced Series Resistance Imaging for Silicon Solar Cells via Electroluminescence

Herein, a method for advanced series resistance imaging via electroluminescence (EL) for silicon solar cells is presented. The well‐known method by Haunschild et al. is revisited. The Fuyuki assumption of a linear relation between diffusion length and EL signal is shown to be not applicable to silicon devices nowadays due to larger minority charge carrier diffusion lengths and thinner solar cells. A new relation derived by Breitenstein is used here instead. The updated method for series resistance and saturation current imaging based on two EL images, which show a far superior separation of contrast and almost 60% shorter data acquisition times in comparison with the original method by Haunschild, is presented. The Weber contrast of the unwanted signal caused by recombination in resistance image is reduced from 0.89 to 0.44, using the advanced method for a prominent feature on the sample cell. The contrast due to resistance stays at the same level. The dark saturation current density images show 20% higher peaks at recombination active areas and also a 5% low.

Detection of 9.5 μm CO2 laser pulses in indium doped PbTe p-n junction

A unique feature of the PbTe semiconductor is the growth of its forbidden energy gap with increasing temperature. This allows saving diode-typical characteristics at temperatures up to 180 K. PbTe p-n diodes were fabricated by means of indium donor diffusion into PbTe single crystals grown using the Czochralski technique. The dark saturation current density was ~10−5 A/cm2 at T = 100 K, whereas at T = 180 K it reached ~10−1 A/cm2. The photovoltage signals induced by a pulsed CO2 laser light across PbTe p-n junction were investigated over the 100–180 K temperature range. The two-photon absorption-caused photovoltaic effect is observed for the first time in In doped PbTe p-n junction for 9.5 μm wavelength at T = 100 K.

A round Robin-Highliting on the passivating contact technology

The aim of this work is to demonstrate the maturity of the TOPCon technology by conducting a round-robin on symmetrically processed lifetime samples in the leading European PV institutes EPFL, ISC, CEA-INES, ISFH, IMEC and Fraunhofer ISE within the H2020 funded project called HighLite. For all layers, dark saturation current-densities ranging between 2 and 10 fA/cm2 can be reported. Simultaneously, no metal induced recombination for the two lower sintering temperatures have been observed pointing towards a true passivated contact. Furthermore, contact resistivities below 10 mΩcm2 have been achieved. It seems that the industrial passivating contact matured to a fully passivated and conducting contact enabling full efficiency potential. The fact that this can be realized using either PECVD or LPCVD from various manufacturer is expected to drive costs down and contribute to the increased adoption of the TOPCon technology.

Recombination and Resistive Losses of Transferred Foil Contacts for Silicon Heterojunction Solar Cells

Silicon heterojunction (SHJ) solar cells have been studied extensively due to their potential to reach high energy conversion efficiencies. However, one of the limiting factors for this technology is the metallization, which uses low‐curing‐temperature silver pastes that result in fingers with higher bulk resistivity. Herein, a simple approach to fabricate the SHJ solar cell contacts is demonstrated with commercially available low‐cost silver (Ag) electrically conductive adhesive (ECA) pastes and aluminium (Al) foils. This technique can result in a transparent conductive oxide (TCO)‐free cell structure and has the potential to combine cell metallization and interconnection. Recombination and resistive loss analyses are performed on the fabricated test samples. A dark saturation current density at the contact (J0c) of 3.05 fA cm−2 for test samples before annealing is reported. The analysis of the experimental and simulated photoluminescence (PL) images shows negligible added recombination. The contact resistivity (ρc) value is 49.3 mΩ cm2 after annealing which can be optimized by specialized ECA pastes.

Study of surface photovoltage spectrum in p+-GaAs/p-GaAlAs/p-GaAs structures

Surface photovoltage (SPV) in p+-GaAs/p-GaAlAs/p-GaAs has been studied by establishing a multilayer model and measuring the SPV at room temperature. The model mainly considers surface recombination velocity, interface recombination velocity and the space charge region (SCR) at the surface of p+-GaAs. The SPV of the multilayer structure is shown to originate predominantly from the minority carrier diffusion, which caused photovoltage between the surface and bottom. Subsequently, the minority carrier diffusion lengths in p+-GaAs and in p-GaAs are obtained from fitting experimental data to the theoretical model. At the same time, the minority carrier diffusion length in p-GaAs is obtained by illuminating the backside (illuminating on p-GaAs) of the p+-GaAs/p-GaAlAs/p-GaAs. The p+-GaAs in p+-GaAs/p-GaAlAs/p-GaAs structure with different thickness are measured to show the variation of SPS with different thickness, but the experimental parameters are not affected. In multi-layer structure, the SPV contributed by different layers has a great difference with different dark saturation current density.

A Mixed-Phase SiOx Hole Selective Junction Compatible With High Temperatures Used in Industrial Solar Cell Manufacturing

We present a p-type passivating rear contact that complies with integration into standard solar cell manufacturing with phosphorus-diffused front side. Our contact structure consists of a thin SiOx tunneling layer grown by wet chemistry and a stack of layers deposited in one single run by plasma-enhanced chemical vapor deposition. The layers of the stack were tailored to protect the interfacial oxide layer, to act as a source for boron diffusion into the wafer and to connect to the external metallisation with low contact resistivity. We found that this stack tolerated annealing at 900 °C over a wide range of dwell times: for 15 min anneals we obtained dark saturation current densities (Jo) as low as 10 fA·cm−2 (after hydrogenation) and after 12-fold increase of the annealing time to 180 min, J0 was only increased to 12 fA·cm−2. These values corresponded to implied open circuit voltages ( i Voc) of 718 and 715 mV, respectively. To test passivating rear contacts under realistic operation conditions, we combined them with an n-type heterojunction into hybrid solar cells. With conversion efficiencies abovementioned 22% and Voc > 705 mV, these devices demonstrated high level of rear surface passivation. Finally, we demonstrated the integration of the hole selective rear contact with a POCl3 diffusion process. To this end, we added a phosphorus diffusion barrier to our layer stack by depositing one additional layer of amorphous SiOx on top of the stack. For symmetric samples with this layer structure on both sides, we observed i Voc values of 714 and 712 mV on n- and p-type silicon wafers after hydrogenation, respectively. Co-diffused cells with POCl3 front diffused emitter and rear passivating contact resulted so far in efficiencies of 20.4% and 20.1% for n- and p-type wafers, respectively.

A Comprehensive Evaluation of Contact Recombination and Contact Resistivity Losses in Industrial Silicon Solar Cells

Reliable characterization techniques to accurately quantify the metallization-induced recombination losses as well as contact resistivity losses of screen-printed cells are crucial for successful optimization of the contact grid design. Previously, the dark saturation current density at the contact ( ${J}_{\rm 0c}$ ) is often assumed to be constant for different finger width. Similarly, impact of finger width on contact resistivity ( ${\rho }_{\rm c}$ ) is rarely reported. Therefore, we performed a comprehensive evaluation of ${J}_{\rm 0c}$ and ${\rho }_{\rm c}$ as a function of finger width, spacing as well as firing temperature. We found out that ${J}_{\rm 0c}$ increases from $\approx$ 2000 to $\approx$ 8100 $\text{fA/cm}^{2}$ , when the finger width increases from 60 to 400 $\mu$ m; and ${\rho }_{\rm c}$ decrease from 7.2 to 2.2 $\text{m}{\Omega }\cdot \text{cm}^{2}$ when using a wide -TLM rather than a narrow -TLM structure, for samples fired at 840 $^{\circ }$ C. Based on our cross-sectional and top-down scanning electron microscopy images, we believe that the physical root cause can be explained by the difference in the microstructure formed at the metal–silicon interface during the firing process for the screen-printed contacts.

Comparative Study of the Electrical Parameters of Individual Solar Cells in a c-Si Module Extracted Using Indoor and Outdoor Electroluminescence Imaging

In this article, electroluminescence (EL) imaging is applied to characterize monocrystalline silicon photovoltaic (PV) modules under indoor and outdoor conditions. EL images of PV modules are analyzed to extract dark saturation current density and series resistance for individual cells within the module. These individual solar cells' parameters together with the terminal voltages of the modules, are used to model the current-voltage (I-V) characteristics of individual cells and the module using the one-diode model of solar cells and LTspice. We have explored the method for both indoor and outdoor EL images and compared the results with indoor I-V measurements under standard test conditions (STC). The electrical parameters of the PV module estimated using this approach for both, indoor and outdoor EL measurements are in good agreement with a relatively small deviation of less than 3% from the reference measurements performed under STC. This method is particularly useful to extract the electrical parameter and information on module degradation in the field using the EL only, without performing an I-V measurement.

In-situ phosphorus-doped polysilicon prepared using rapid-thermal anneal (RTA) and its application for polysilicon passivated-contact solar cells

A rapid thermal anneal (RTA) is used to crystallize the plasma-enhanced chemical vapor deposition (PECVD) deposited hydrogenated amorphous silicon (a-Si:H) thin film to form the phosphorus-doped polysilicon passivated contact in tunnel oxide passivated contact (TOPCon) solar cells. The effects of annealing temperature, annealing time, cooling time, and the polysilicon thickness on the surface passivation are investigated. The primary advantage of the RTA is reducing the whole crystallization period to ~15 min, shorter than the conventional tube-furnace annealing period of >60 min. We find that the RTA is a robust method to prepare high-quality polysilicon passivated contact without introducing blistering when the thickness of the a-Si:H is less than 40 nm. The optimized RTA process leads to an implied open-circuit voltage (iVoc) of 712 mV and a single-sided dark saturation current density (J0,s) of 12.5 fA/cm2 in the as-annealed state, which is inferior to the surface passivation of the controlled one prepared by a tube furnace annealing. Fortunately, a subsequent Al2O3 capping hydrogenation improves the iVoc and J0,s to 727 mV and 4.7 fA/cm2, respectively. The champion conversion efficiency of 23.04% (Voc = 679.0 mV, Jsc = 41.97 mA/cm2 and FF = 80.86%) is achieved, which demonstrates the effectiveness of RTA for preparing a high-efficiency polysilicon passivated-contact solar cell.