We report the electrical properties of an AlGaN/GaN high-electron-mobility transistor (HEMT) with epitaxial Nd2O3 as a gate insulator. The introduction of Nd2O3 between the metal and the semiconductor in the gate region results in a tenfold reduction in gate leakage current. The transconductance remains at its peak over a significant range of gate bias (4.5 V), and the transconductance flatness is maintained at an elevated temperature of 200 C-degrees. This linearity is attributed to the increased electron concentration in the channel due to the introduction of epitaxial Nd2O3 and the resulting strain on the AlGaN barrier layer. The increased two-dimensional electron gas density also leads to an increase in the maximum output drain current in the case of the metal-oxide-semiconductor HEMT compared to the standard metal-semiconductor HEMT used as the control sample.

This letter reports electrical properties of Al-GaN/GaN high electron mobility transistor (HEMT) with epitaxial Nd2O3 as a gate insulator. The introduction of Nd2O3 between metal and semiconductor in the gate region, results in two orders of magnitude reduction of gate leakage current, which remains unchanged even at higher temperature of 200°C. The Ion/I off also remains constant at 200°C and the transconductance stays at its peak over a significant range of gate bias (4.5 V). This linearity is attributed to the increased electron concentration in channel due to introduction of epitaxial Nd2O3 and the resulting strain on AlGaN barrier layer. The increased 2DEG density also leads to an increase in output drain current from the metal oxide semiconductor(MOS)-HEMT.

In this article, we report the temperature-dependent transistor characteristics of Epi-Nd2O3/AlGaN/GaN MOSHEMT. The entire heterostructure, including epi-Nd2O3, is grown by Molecular Beam Epitaxy technique (MBE). The introduction of an epitaxial rare earth oxide reduces the OFF current of the transistor while it also makes it temperature independent at least up to 473 K [9]. The thickness of the oxide taken is 5.2 nm. It is observed here that the gate leakage current of all epitaxy MOSHEMT measured at 298 K and at 473 K, respectively, remains unchanged. The I-on/I-off ratio of the MOSHEMT is seen to improve by an order of magnitude approximately 2 as compared to metal semiconductor HEMT (MSHEMT). The ON current of the transistor is observed to decrease with an increase in temperature because of polar optical phonon scattering. Reliability study by application of bias thermal stress is also done for the fabricated MOSHEMT.

Large surface area applications such as high-efficiency > 26% solar cells require surface patterning with 1-10 micrometers periodic patterns at high fidelity over 1-10 cm^2 areas (before up scaling to 1 m^2) to perform at, or exceed, the Lambertian (ray optics) limit of light trapping. Here we show a pathway to high-resolution sub-1 micrometer etch mask patterning by ablation using direct femtosecond laser writing performed at room conditions (without the need for a vacuum-based lithography approach). A Bessel beam was used to alleviate the required high surface tracking tolerance for ablation of 0.3-0.8 micrometer diameter holes in ~40 nm alumina Al2O3-mask at high writing speed, 7.5 cm/s; a patterning rate 1 cm^2 per 20 min. The plasma etching protocol was optimised for a zero-mesa formation of photonic crystal (PhC) trapping structures and smooth surfaces at the nanoscale level. Scaling up in area and throughput of the demonstrated approach is outlined.

AbstractFabrication and characterization of solar cells based on multicrystalline silicon (mc‐Si) thin films are described and synthesized from low‐cost soda‐lime glass (SLG). The aluminothermic redox reaction of the silicon oxide in SLG during low‐temperature annealing at 600 – 650 °C leads to an mc‐Si thin film with large grains of lateral dimensions in the millimeter range, and moderate p‐type conductivity with an average Al acceptor concentration between 5 × 1016 and 1.2 × 1017 cm−3 in the bulk. A residual composite layer of mainly alumina and unreacted Al forms beneath the mc‐Si thin film as the second product of the crystalline silicon synthesis (CSS) process, which can be used as rear contact in a vertical solar cell design. The mc‐Si absorber (≈10 µm) is thin enough that the diffusion length given by a minority carrier lifetime of ≈1 µs exceeds the path length to the top contact several times. Homojunction and heterojunction diodes have been fabricated on the mc‐Si thin films and show great potential of CSS for the realization of high‐performance solar cells.

Fast changing irradiation on vehicle‐integrated photovoltaic (VIPV) modules may impose demanding requirements for maximum power point tracking (MPPT) to ensure high energy conversion efficiency. In this work, the results of simulations regarding the output and efficiency of an exemplary VIPV module under real‐life irradiation conditions as measured with high time resolution are resulted. Herein, resistive as well as voltage source load is used as two idealized models of the MPPT. The simulations show that, in most cases, tracking with a resistive load at 1 Hz preserves above 90%relof the convertible energy determined by the cell performances under given irradiance levels. With a voltage source load, these values do not undercut 97%relat 0.1 Hz. Herein, it is also found that partial shading across the exemplary series connected module can reduce the converted energy in the range of 5–10%relin relation to complete negligence of this effect.

In this article, we report the temperature-dependent transistor characteristics of Epi-Nd <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> /AlGaN/GaN MOSHEMT. The entire heterostructure, including epi-Nd <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> , is grown by Molecular Beam Epitaxy technique (MBE). The introduction of an epitaxial rare earth oxide reduces the OFF current of the transistor while it also makes it temperature independent at least up to 473 K [9]. The thickness of the oxide taken is 5.2 nm. It is observed here that the gate leakage current of all epitaxy MOSHEMT measured at 298 K and at 473 K, respectively, remains unchanged. The I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</inf> /I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</inf> ratio of the MOSHEMT is seen to improve by an order of magnitude approximately 2 as compared to metal semiconductor HEMT (MSHEMT). The ON current of the transistor is observed to decrease with an increase in temperature because of polar optical phonon scattering. Reliability study by application of bias thermal stress is also done for the fabricated MOSHEMT.

In addition to excellent surface passivation and carrier selectivity, the structure based on the heavily doped polysilicon layer on an ultrathin silicon oxide interlayer also demonstrates strong impurity gettering effects. Herein, the gettering strength of a range of phosphorus‐ or boron‐doped polysilicon films from different fabrication techniques is assessed and compared. Iron, one of the most common metallic impurities in silicon, is used as a tracer impurity to quantify the gettering strength (segregation coefficient). A comparison of the experimental results to the literature, combined with measurements of the electrically active and inactive dopant concentrations, enables us to suggest the main gettering mechanisms in different polysilicon films. The differences in the segregation coefficients of the phosphorus‐doped polysilicon films for iron are within one order of magnitude, in spite of their different combinations of gettering mechanisms. On the other hand, boron‐doped polysilicon films show a large variation in their gettering effects, although the predominant gettering mechanisms are all attributed to electrically inactive boron, according to the current understanding of the gettering mechanisms from the literature. Finally, the impact of different polysilicon gettering effects on the efficiency of tunnel oxide‐passivated contact (TOPCon) cells is simulated and discussed.

The commonly observed absorption around 265 nm in AlN is hampering the outcoupling efficiency of light‐emitting diodes (LEDs) emitting in the UV‐C regime. Carbon impurities in the nitrogen sublattice (C N ) of AlN are believed to be the origin of this absorption. A specially tailored experiment using a combination of ion implantation of boron, carbon, and neon with subsequent high‐temperature annealing allows to separate the influence of intrinsic point defects and carbon impurities regarding this absorption. Herein, the presented results reveal the relevance of the intrinsic nitrogen‐vacancy defect V N . This is in contradiction to the established explanation based on C N defects as the defect causing the 265 nm absorption and will be crucial for further UV‐LED improvement. Finally, in this article, a new interpretation of the 265 nm absorption is introduced, which is corroborated by density functional theory (DFT) results from the past decade, which are reviewed and discussed based on the new findings.

For vehicle integrated photovoltaics (VIPV) there are possibly specific requirements on the speed of maximum power point tracking. However, a certain delay in the response of solar cells to fast irradiance changes might impact those requirements on the MPPT. The subject of this work is therefore the investigation of the transient electrical behaviour of state-of-the-art silicon heterojunction solar cells. We use a fast switchable LED-array and an oscilloscope to investigate the cell voltage of silicon heterojunction solar cells under transient illumination. We find that these cells have a switch-off delay that is smaller than one millisecond when operated at or close to the maximum power point. This can be assumed to be faster than the time scale on that irradiances change typically occur on a car body while driving. We also find that, after switching off the light source, the transient cell voltage does not show a simple capacitive behaviour, but a more complex characteristic. A theoretical analysis shows that this behaviour can be explained by the nonlinear dependency of the diffusion and depletion capacitance and the minority carrier lifetime on the cell voltage.

Vehicle integrated photovoltaic (VIPV) systems have much different requirements on maximum power tracking compared to stationary setups. The occurrence of fast changes between full irradiance and shading are demanding. To evaluate the specific impact of these conditions on the specifications of VIPV systems, we conduct high resolution measurements of the incident irradiance onto a car body while driving. We investigate the influence of environmental conditions like weather, season and building density in an urban environment on measured irradiance on the roof and the sides of a vehicle. We find that weather conditions have the highest impact on the measured irradiance on the roof, while the relative irradiance on the side depends more heavily on the season. We also find that changes in irradiance occur predominantly at frequencies below 1 Hz, but changes with 100 Hz or more can occur in certain situations, with a tendency toward higher frequencies for sunny weather. This must be considered in maximum power point tracker design.

Polycrystalline-silicon/oxide (poly-Si/SiOx) passivating contacts for high efficiency solar cells exhibit excellent surface passivation, carrier selectivity, and impurity gettering effects. However, the ultrathin SiOx interlayer can act as a diffusion barrier for metal impurities and this potentially slows down the overall gettering rate of the poly-Si/SiOx structures. Herein, the factors that determine the blocking effects of the SiOx interlayers are identified and investigated by examining two general types of the SiOx interlayers: 1.3-nm ultrathin tunneling SiOx with negligible pinholes and 2.5-nm SiOx with thermally created pinholes. Iron is used as a tracer impurity in silicon to quantify the gettering rate. By fitting the experimental gettering kinetics by a diffusion-limited segregation gettering model, the blocking effects of the SiOx interlayers are quantified by a transport parameter. Both the oxide stoichiometry and pinhole density affect the effective transport of iron through SiOx interlayers. The oxide stoichiometry depends strongly on the oxidation method, while the pinhole density is affected by the activation temperature, doping concentration, doping technique, and possibly the dopant type as well. To enable a fast gettering process during typical high-temperature formation of the poly-Si/SiOx structures, a SiOx interlayer that is less stoichiometric or with a higher pinhole density is preferred.

Polycrystalline‐silicon/oxide (poly‐Si/SiO x ) passivating contacts for high efficiency solar cells exhibit excellent surface passivation, carrier selectivity, and impurity gettering effects. However, the ultrathin SiO x interlayer can act as a diffusion barrier for metal impurities and this potentially slows down the overall gettering rate of the poly‐Si/SiO x structures. Herein, the factors that determine the blocking effects of the SiO x interlayers are identified and investigated by examining two general types of the SiO x interlayers: 1.3 nm ultrathin tunneling SiO x with negligible pinholes and 2.5 nm SiO x with thermally created pinholes. Iron is used as tracer impurity in silicon to quantify the gettering rate. By fitting the experimental gettering kinetics by a diffusion‐limited segregation gettering model, the blocking effects of the SiO x interlayers are quantified by a transport parameter. Both the oxide stoichiometry and pinhole density affect the effective transport of iron through SiO x interlayers. The oxide stoichiometry depends strongly on the oxidation method, while the pinhole density is affected by the activation temperature, doping concentration, doping technique, and possibly the dopant type as well. To enable a fast gettering process during typical high‐temperature formation of the poly‐Si/SiO x structures, a SiO x interlayer that is less stoichiometric or with a higher pinhole density is preferred.

Passivating contacts consisting of heavily doped polycrystalline silicon (poly-Si) and ultrathin interfacial silicon oxide (SiOx) films enable the fabrication of high-efficiency Si solar cells. The electrical properties and working mechanism of such poly-Si passivating contacts depend on the distribution of dopants at their interface with the underlying Si substrate of solar cells. Therefore, this distribution, particularly in the vicinity of pinholes in the SiOx film, is investigated in this work. Technology computer-aided design (TCAD) simulations were performed to study the diffusion of dopants, both phosphorus (P) and boron (B), from the poly-Si film into the Si substrate during the annealing process typically applied to poly-Si passivating contacts. The simulated 2D doping profiles indicate enhanced diffusion under pinholes, yielding deeper semicircular regions of increased doping compared to regions far removed from the pinholes. Such regions with locally enhanced doping were also experimentally demonstrated using high-resolution (5-10 nm/pixel) scanning spreading resistance microscopy (SSRM) for the first time. The SSRM measurements were performed on a variety of poly-Si passivating contacts, fabricated using different approaches by multiple research institutes, and the regions of doping enhancement were detected on samples where the presence of pinholes had been reported in the related literature. These findings can contribute to a better understanding, more accurate modeling, and optimization of poly-Si passivating contacts, which are increasingly being introduced in the mass production of Si solar cells.

Stability of the passivation quality of poly‐Si on oxide junctions against the conventional mainstream high‐temperature screen‐print firing processes is highly desirable and also expected since the poly‐Si on oxide preparation occurs at higher temperatures and for longer durations than firing. We measure recombination current densities (J0) and interface state densities (Dit) of symmetrical samples with n‐type poly‐Si contacts before and after firing. Samples without a capping dielectric layer show a significant deterioration of the passivation quality during firing. The Dit values are (3 ± 0.2) × 1011 and (8 ± 2) × 1011 eV/cm2 when fired at 620°C and 900°C, respectively. The activation energy in an Arrhenius fit of Dit versus the firing temperature is 0.30 ± 0.03 eV. This indicates that thermally induced desorption of hydrogen from SiH bonds at the poly‐Si/SiOx interface is not the root cause of depassivation. Postfiring annealing at 425°C can improve the passivation again. Samples with SiNx capping layers show an increase in J0 up to about 100 fA/cm2 by firing, which can be attributed to blistering and is not reversed by annealing at 425°C. On the other hand, blistering does not occur in poly‐Si samples capped with AlOx layers or AlOx/SiNy stacks, and J0 values of 2–5 fA/cm2 can be achieved after firing. Those findings suggest that a combination of two effects might be the root cause of the increase in J0 and Dit: thermal stress at the SiOz interface during firing and blistering. Blistering is presumed to occur when the hydrogen concentration in the capping layers exceeds a certain level.

We demonstrate the fabrication of a fully screen‐printed p‐type silicon solar cell with local hole‐collecting Al‐alloyed (Al‐p + ) contacts with a record open circuit voltage of 716 mV. The solar cell is fabricated by using almost the same process equipment as PERC cells. One of the dominant recombination losses in PERC cells is the recombination in the passivated and in the contacted emitter regions that so far limit the open circuit voltage to values below 700 mV. We eliminate these loss channels by substituting the P‐diffused emitter by a passivating n‐type poly‐Silicon on Oxide (nPOLO) contact. We place this contact on the rear side because of its otherwise strong parasitic absorption. The Al‐p + contacts are also located at the rear side to avoid front‐side shading. This results in a POLO‐IBC cell structure. The efficiency of the best cell so far is 23.0% with a designated area of 4 cm 2 fabricated on a M2‐sized wafer. Scanning electron microscopy reveals an Al‐p + thickness of less than 3.3 μm and only a few 100 nm at the contact ends, which is less than the 5 μm typically for optimized Al‐p + contacts. A comparison of measured and simulated current‐voltage curves over a variation of the contact fraction extracts a high saturation current density of the Al‐p + contact of J 0‐Al ‐p+ = 2,250 fA cm −2 for the current screen‐print conditions and Al‐paste causing an absolute efficiency loss of 0.5% abs . The recombination at the AlO x /SiN y surface and the shunt resistance limits the cell by 0.6% abs each.

The setting up of a practical electrically driven light commercial demonstration vehicle with integrated photovoltaics (PV) is reported. The demonstrator vehicle is equipped with 15 modules based on the crystalline Si/amorphous Si heterojunction technology. The nominal total peak power under standard testing conditions is 2180 Wp. Specifically, the PV‐converted energy is fed into the high‐voltage (HV; 400 V) board‐net for a utilization of the large capacity of the HV battery and thus for direct range extension. The demonstrator vehicle is equipped with irradiation, wind, temperature, magnetic, and global positioning system sensors. Irradiation and temperature as well as the energy flows from modules, maximum power point trackers (MPPTs), low‐voltage buffer battery to HV battery via DC/DC, and from the HV battery to the loads during an exemplarily test drive day (May 31, 2021) are monitored. The range extension obtained at this day on our test route (51° 59′ N, 9° 31′ E) was 36 km, the corresponding CO2 savings account for ≈2.3 kg. The chain efficiency of the electronic components from the input side of the MPPTs to the HV output side of the DC/DC was 68.6%, whereas the DC/DC itself has an average efficiency of 90%.

Polysilicon-on-oxide (POLO) passivating contacts and interdigitated back-contact (IBC) cell technologies have recently attracted a lot of interest as candidates for the implementation in the next generation of solar cells. An IBC cell with POLO junctions for both polarities − a POLO2-IBC cell − has to electrically isolate the highly defective p+ and n+ poly-Si regions on the rear side of the cell to avoid parasitic recombination. Inserting an initially undoped, intrinsic (i) region between the p+ and n+ poly-Si regions was demonstrated to successfully prevent the parasitic recombination in the transition region of ISFH's 26.1%-efficient POLO2-IBC cell. In order to further improve the conversion efficiency towards 27%, we apply hydrogen-donating dielectric layer stacks to the p+-(i)-n+ POLO interdigitating rear side to enhance the passivation quality of the POLO junctions. We indeed show a significant improvement of POLO junctions on symmetrical full-area homogenously doped reference samples, but when we apply a hydrogen-donating layer stack on the p+-(i)-n+ POLO interdigitating rear side, we observe a strong degradation in the performance of the POLO2-IBC cell. We attribute this to the formation of a conductive channel between the p+ and n+ poly-Si regions due to the strong negative charge density of the hydrogen-donating layer stack.