N-type Crystalline Silicon Substrates Research Articles

Investigation of the effect of oxygen flow modulation on ITO film properties to improve the performance of SHJ solar cells

Photovoltaics offer a sustainable solution for the growing energy needs of the world, while reducing environmental impact. Transparent Conductive Oxides (TCOs), which are essential in photovoltaic technology, offer high light transmittance and effective charge carrier extraction. This research focuses on the impact of oxygen (O2) flow rates in the deposition of indium tin oxide (ITO) films on n-type crystalline silicon (c-Si) substrates by DC magnetron sputtering. The structural, optical, and electrical properties were analyzed. Based on the results, the optimal O2 ratio was determined and used in the fabrication of SHJ solar cells, achieving an efficiency of 18.6%.

Effects of Chamber Pressures on the Passivation Layer of Hydrogenated Nano-Crystalline Silicon Mixed-Phase Thin Film by Using Microwave Annealing

This paper proposes the effects of chamber pressures on the passivation layer of hydrogenated nano-crystalline silicon (nc-Si:H) mixed-phase thin film using microwave annealing (MWA) to achieve a high-quality thin film. The use of 40.68 MHz very-high-frequency plasma-enhanced chemical vapor deposition (VHFPECVD) deposited the nc-Si:H mixed-phase thin film on the top and bottom of the n-type crystalline silicon substrate. The chamber pressures (0.2, 0.4, 0.6, and 0.8 Torr) of the VHFPECVD were critical factors in controlling the carrier lifetime of the symmetric structure. By using the VHFPECVD to deposit the nc-Si:H and using the MWA to enhance the quality of the symmetric structure, the deposited nc-Si:H’s properties of a crystalline volume fraction of 29.6%, an optical bandgap of 1.744 eV, and a carrier lifetime of 2942.36 μs were well achieved, and could be valuable in thin-film solar-cell applications.

Fabrication of Tantalum-Doped Titanium-Oxide Electron-Selective Contacts with High Passivation Quality

In this paper, we report on the fabrication of Ta-doped TiO2 (TiO2:Ta) electron-selective contacts and their improved passivation qualities. By using thermal atomic layer deposition, 3.5 nm-thick, undoped TiO2 films and 3.5 nm-thick TiO2:Ta films with Ta concentrations of 1.5, 2.8, and 5.5 at.% were formed at 150 °C on n-type crystalline silicon substrates with ∼1 nm-thick chemical SiO2 layers. Rutherford backscattering spectroscopic measurements confirmed the Ta concentrations in the films and uniform distributions of Ta atoms in the films. X-ray photoelectron spectrometry measurements implied that Ta atoms rather cause local structural changes than enter substitutionally into Ti sites. After annealing at 130 °C in air, the effective minority carrier lifetime (τ eff) of the TiO2:Ta-passivated samples were significantly higher than those of the samples passivated with undoped TiO2 films. The highest τ eff was obtained for the samples with a relatively low Ta-doping concentration of 1.5 at.%. On the other hand, the passivation quality was degraded by Ta doping with a too high concentration (for example, 18.4 at.%). These results indicate that moderate Ta doping improves the passivation quality of TiO2 thin films.

Improvement in the passivation quality of titanium oxide thin films by doping with tantalum

We demonstrate that the passivation quality of TiO2 electron-selective contacts can be improved by Ta doping. By using atomic layer deposition, 3.5-nm-thick, undoped TiO2 films and Ta-doped TiO2 (TiO2:Ta) films with Ta concentrations of 1.5, 2.8, and 5.5 at.% were formed on n-type crystalline silicon substrates with chemical SiO2 layers. After annealing at 130 °C, the effective minority-carrier lifetime (τeff) of the TiO2:Ta-passivated samples were significantly higher than that of the undoped-TiO2-passivated samples, and the highest τeff was obtained at a relatively low Ta-doping concentration of 1.5 at.%. These indicate that moderate Ta doping improves the passivation quality of TiO2 thin films.

Observation of photovoltaic effect within locally doped silicon nanojunctions using conductive probe AFM

Abstract Localized p-doped nanojunctions (200–300 nm in diameter) were formed in n-type crystalline silicon substrates and were characterized using scanning electron microscopy (SEM) and conductive-probe atomic force microscopy (C-AFM). Localized doping was performed by diffusion through sub-micron sized holes in a silicon-oxide mask defined using self-organized polystyrene nanoparticles. After oxide removal, a significant brightness contrast in the SEM top and side view images strongly suggested the successful local doping of these areas. Furthermore, local current-voltage measurements performed by C-AFM revealed an open circuit voltage and a short-circuit current only in the areas defined as nanojunctions. This photovoltaic effect is driven by the laser used to control cantilever deflection in the AFM.

Direct observation of changes in the effective minority-carrier lifetime of SiNx-passivated n-type crystalline-silicon substrates caused by potential-induced degradation and recovery tests

We directly observed reductions in the effective minority-carrier lifetime (τeff) of n-type crystalline silicon (c-Si) substrates with silicon-nitride passivation films caused by potential-induced degradation (PID). We prepared PID-test samples by encapsulating the passivated substrates with standard photovoltaic-module encapsulation materials. After PID tests applying −1000V to the c-Si samples from the glass surface, the τeff was decreased, which probably pertains to Na introduced into the c-Si. After PID tests applying +1000V, the sample, on the other hand, showed a considerably rapid τeff reduction, probably associated with the surface polarization effect. We also performed recovery tests of predegraded samples, by applying a bias opposite to that used in a degradation test. The τeff of a sample predegraded by applying +1000V was rapidly completely recovered by applying −1000V, while those of predegraded by applying −1000V show only slight and insufficient τeff recovery.

The bifunctional tin-doped indium oxide as hole-selective contact and collector in silicon heterojunction solar cell with a stable intermediate oxide layer

The tin-doped indium oxide (ITO) and the intermediate nanometer-scale SiOx layers were synthesized directly on n-type crystalline silicon (n-Si) substrate by radio-frequency magnetron sputtering deposition. During the ITO-sputtering deposition, the effect of shallow implantation intermixing led to forming an ultra-thin SiOx layer, which could successfully lessen the interface states and promote the transportation of carriers. The photovoltaic properties of devices showed the open-circuit voltage (Voc) strongly correlated to the carrier concentration of ITO (nITO), indicating a hole-selective contact of ITO. An equivalent “p-type Fermi level” (hole as majority carriers) was reasonably employed to interpret the decrease of Voc with the increase of nITO. The impact of the work function difference between ITO and n-Si on Voc of ITO/SiOx/n-Si heterojunction cells was tentatively equivalent to the difference of the defined quasi-Fermi levels. Through the modification of surface-reflectance and rear contact, the heterojunction structure solar cells achieved efficiency of 11.50 ± 0.17%. Furthermore, the stability of the devices in conversion efficiency was excellent over a whole year. The temperature coefficient of −0.34%/°C was obtained, which was better than −0.45%/°C of a typical diffused-junction silicon solar cell.

Composition of nanocomposites based on thin layers of tin on porous silicon formed by magnetron sputtering

Using scanning electron microscopy and X-ray photoelectron spectroscopy the features of morphology and peculiarities of the surface composition of nanocomposites made of thin tin layers by magnetron sputtering formed on porous silicon with pores size of 50–150nm. Porous silicon was obtained on n-type conductivity crystalline silicon substrate. The obtained nanocomposites were found differ between themselves by the ratio of the main phases: tin dioxide, sub-oxide and metal tin in a dependence on the thickness of the deposited tin layer. Fraction of the oxidized tin in the phase composition of composites was reduced from the surface to the bulk of the sample. Moreover, it was determined that the deposition of tin nanolayers did not result in a considerable change of the phase composition of porous silicon substrate.

Boron Emitter Formation by Plasma Immersion Ion Implantation in n-type PERT Silicon Solar Cells

The use of plasma immersion ion implantation (PIII) is a relevant approach for the development of advanced solar cells technologies at lower cost (€/Wp). In this paper, we report on the development of homogeneous boron (B) doping of n-type crystalline silicon (cSi) substrate by the PIII technique. Using diborane (B2H6) as gas precursor, various doping profiles were identified fitting the requirements for boron-doped emitters in n-type PERT solar cells. Particularly, saturation current density (J0e) of 50 fA/cm2 were achieved on symmetrical samples for a 94 Ω/sg textured B-emitter passivated with SiO2/SiN stack. Bifacial n-type Passivated Emitter Rear Totally-diffused (n-PERT) solar cells were fabricated using the PIII technology and conversion efficiencies up to 19.8% on 239 cm2 Cz-Si wafers were obtained. As a consequence, these results indicate that PIII can compete with beamline technology but will have lower running cost. It is therefore a promising technology to create high efficiency cSi solar cells.

Electrical Hole Transport Properties of an Ambipolar Organic Compound With Zn-Atoms on a Crystalline Silicon Heterostructure

In this paper, we investigate the electrical hole transport properties of an organic/inorganic heterostructure consisting of a thin organic film, that combines hole and electron conducting molecules around a bridging Zn-atom, deposited on top of an n-type crystalline silicon substrate. Current-voltage characteristics and capacitance voltage measurements have been used for the determination of the organic layer dielectric and hole conduction parameters.

Surface passivation and optical characterization of Al2O3/a-SiCx stacks on c-Si substrates

The aim of this work is to study the surface passivation of aluminum oxide/amorphous silicon carbide (Al2O3/a-SiCx) stacks on both p-type and n-type crystalline silicon (c-Si) substrates as well as the optical characterization of these stacks. Al2O3 films of different thicknesses were deposited by thermal atomic layer deposition (ALD) at 200 °C and were complemented with a layer of a-SiCx deposited by plasma-enhanced chemical vapor deposition (PECVD) to form anti-reflection coating (ARC) stacks with a total thickness of 75 nm. A comparative study has been carried out on polished and randomly textured wafers. We have experimentally determined the optimum thickness of the stack for photovoltaic applications by minimizing the reflection losses over a wide wavelength range (300–1200 nm) without compromising the outstanding passivation properties of the Al2O3 films. The upper limit of the surface recombination velocity (Seff,max) was evaluated at a carrier injection level corresponding to 1-sun illumination, which led to values below 10 cm/s. Reflectance values below 2% were measured on textured samples over the wavelength range of 450–1000 nm.

Advancements in n‐Type Base Crystalline Silicon Solar Cells and Their Emergence in the Photovoltaic Industry

The p-type crystalline silicon wafers have occupied most of the solar cell market today. However, modules made with n-type crystalline silicon wafers are actually the most efficient modules up to date. This is because the material properties offered by n-type crystalline silicon substrates are suitable for higher efficiencies. Properties such as the absence of boron-oxygen related defects and a greater tolerance to key metal impurities by n-type crystalline silicon substrates are major factors that underline the efficiency of n-type crystalline silicon wafer modules. The bi-facial design of n-type cells with good rear-side electronic and optical properties on an industrial scale can be shaped as well. Furthermore, the development in the industrialization of solar cell designs based on n-type crystalline silicon substrates also highlights its boost in the contributions to the photovoltaic industry. In this paper, a review of various solar cell structures that can be realized on n-type crystalline silicon substrates will be given. Moreover, the current standing of solar cell technology based on n-type substrates and its contribution in photovoltaic industry will also be discussed.

수소 희석비에 따른 실리콘 이종접합 계면에 대한 분석 및 태양전지로의 응용

Hydrogenated amorphous silicon (-Si:H) layers deposited by plasma enhanced chemical vapor deposition (PECVD) are investigated for use in silicon hetero-junction solar cells employing n-type crystalline silicon (c-Si) substrates. The optical and structural properties of silicon hetero-junction devices have been characterized using spectroscopy ellipsometry and high resolution cross-sectional transmission electron micrograph (HRTEM). In addition, the effective carrier lifetime is measured by the quasi-steady-state photocoductance (QSSPC) method. We have studied on the correlation between the order of -Si:H and the passivation quality at the interface of -Si:H/c-Si. Base on the result, we have fabricated a silicon hetero-junction solar cell incorporating the -Si:H passivation layer with on open circuit voltage () of 637 mV.

An ultra-thin Schottky diode as a transmission particle detector forbiological microbeams

We fabricated ultrathin metal-semiconductor Schottkydiodes for use as transmission particle detectors in the biologicalmicrobeam at Columbia University's Radiological Research AcceleratorFacility (RARAF). The RARAF microbeam can deliver a precise dose of ionizingradiation in cell nuclei with sub-micron precision. To ensure an accuratedelivery of charged particles, the facility currently uses a commercialcharged-particle detector placed after the sample. We present here atransmission detector that will be placed between the particle acceleratorand the biological specimen, allowing the irradiation of samples that wouldotherwise block radiation from reaching a detector behind the sample. Fourdetectors were fabricated with co-planar gold and aluminum electrodesthermally evaporated onto etched n-type crystalline silicon substrates, withdevice thicknesses ranging from 8.5 μm - 13.5 μm. We showcoincident detections and pulse-height distributions of charged particles inboth the transmission detector and the commercial detector above it.Detections are demonstrated at a range of operating conditions, includingincoming particle type, count rate, and beam location on the detectors. The13.5 μm detector is shown to work best to detect 2.7 MeV protons(H+), and the 8.5 μm detector is shown to work best to detect 5.4 MeV alpha particles (4He++). The development of a transmissiondetector enables a range of new experiments to take place at RARAF onradiation-stopping samples such as thick tissues, targets that needimmersion microscopy, and integrated microfluidic devices for handlinglarger quantities of cells and small organisms.

Hot wire chemical vapor deposited boron carbide thin film/crystalline silicon diode for neutron detection application

Boron carbide films have been deposited on n-type crystalline silicon substrate by hot wire chemical vapor deposition technique using ortho-carborane precursor. The deposited films have been characterized by secondary ion mass spectrometry for their isotopic study which shows the presence of 10B in the film making them suitable for thermal neutron absorber application. These films have a p-type semiconducting nature and hence can be employed to form a p-n junction with n-type silicon. We have demonstrated for the first time the formation of a p-n junction with films deposited by hot wire chemical vapor deposition technique. The current–voltage characteristics of the diode have been measured and the characteristics show low leakage current (nA) in the reverse bias condition. From capacitance–voltage study, it is observed that the depletion width is of the order of few microns which is sufficient for detection of alpha particle released by 10B in the n, α reaction. The results of this study indicate that hot wire chemical vapor deposited boron carbide/crystalline silicon diode could be used as a compact device for thermal neutron detection.

Electronic structure and formation mechanism of complex Ti–Nb oxide

Two-layer thin film specimens of Nb2O5 and TiO2 were deposited on optical-grade quartz and n-type single crystalline silicon substrates with (100) crystallographic orientation by a magnetron deposition source under high vacuum. All samples were subjected to 1–5h of resistive heating at ultra high vacuum, and in situ X-ray diffraction measurements (XRD) were made in the temperature range of 300–1373K. Analysis of the XRD data confirmed the growth of TiNbO4 during cooling of the two-layered specimens which had been previously heated to 1373K. Optical measurements revealed a band gap value of 3.78eV for the direct transition and 3.29eV for the indirect one. The samples had a transmittance of 85% in the visible range. Electrophysical measurements in high vacuum established the electroresistivity vs. temperature dependence in the range of 300–773K, from 7.3⁎10−1 to 3.9⁎10−2Ω cm, respectively. X-ray photoelectron spectroscopy measurements were used to examine the chemical shift for Nb 3d, with a value of −1.1eV in comparison with Nb5+ and matched to Nb4+[1], while the Ti lines correspond to Ti4+[2].

Photovoltaic Response of Carbon Nanotube-Silicon Heterojunctions: Effect of Nanotube Film Thickness and Number of Walls

We report on the multiwall carbon nanotube application as energy conversion material to fabricate thin film solar cells, with nanotubes acting as photogeneration sites as well as charge separators, collectors and carrier transporters. The device consists of a semitransparent thin film of nanotubes coating a n-type crystalline silicon substrate. Under illumination electron-hole (e-h) pairs, generated in the nanotubes and in the silicon substrate underneath, are split and charges are transported through the nanotubes (electrons) and the n-Si (holes). We found that a suitable thickness of the nanotube thin film, high density of Schottky junctions between nanotubes and n-Si and lowest number of nanotube walls are all fundamental parameters to improve the device incident photon to electron conversion efficiency. Multiwall carbon nanotubes have been synthesized by chemical vapour deposition in an ultra high vacuum chamber by evaporating a given amount of iron at room temperature and then exposing the substrate kept at 800 degrees C at acetylene gas. The amount of deposited iron is found to directly affect the nanotube size distribution (inner and outer diameter) and therefore the number of walls of the nanotubes.

Development of Interdigitated Back Contact Silicon Heterojunction (IBC Si-HJ) Solar Cells

Abstract This study deals with the development and optimization of Interdigitated Back Contact (IBC) Silicon Heterojunction (Si-HJ) solar cells based on n-type crystalline silicon (c-Si) substrates. Both one-dimensional (1D) and 2D aspects of IBC Si-HJ cells are explored in this work. Rear Emitter (RE) Si-HJ cells are fabricated to study the influence of the emitter stack on 1D resistive losses. It is shown that the rear emitter stack has to be carefully designed to maintain a high surface passivation level without inducing series resistance (RSeries). On IBC Si-HJ structures, the influence of 2D features such as emitter contact fraction are confirmed both experimentally and by modeling. Using the screen printing technology, 25 cm2 IBC Si-HJ structures have been fabricated with an efficiency of 15.7%.

I– V characteristics of a-Si–c-Si hetero-junction diodes made by hot wire CVD

p-Type hydrogenated amorphous silicon (a-Si:H) was deposited on n-type crystalline silicon (c-Si) substrates to obtain hetero-junction diodes. Additionally, a thin intrinsic a-Si:H layer was inserted between both the p-type film and the n-type substrate to study its passivation effect on the c-Si surface. The amorphous films were obtained by the hot wire chemical vapor deposition (HWCVD) technique, using a tungsten filament and silane (SiH 4), hydrogen (H 2) and diborane (B 2H 6) gases, where the deposition parameters such as gas flow, substrate temperature and filament temperature were varied. Optical band gap, deposition rate and conductivity were measured for all the films. We studied the influence of the quality of the amorphous films upon the performance of the hetero-junction diodes. In particular, the diode ideality factor ( n) and the saturation current density ( J 0) were determined by measuring the current–voltage characteristics in dark conditions. It is shown that the presence of the intrinsic layer is fundamental for making good diodes, since devices made without this film cause the diodes to have high saturation current density and ideality factor ( J 0>10×10 −6 A/cm 2, n>4) as compared to diodes with a good intrinsic layer ( J 0=5×10 −9 A/cm 2, n=1.39). The results obtained are encouraging, but the quality of the intrinsic films still should be improved for applying them to HIT solar cells.

Carrier transport and sensitivity issues in heterojunction with intrinsic thin layer solar cells on N-type crystalline silicon: A computer simulation study

Heterojunction with intrinsic thin layer or “HIT” solar cells are considered favorable for large-scale manufacturing of solar modules, as they combine the high efficiency of crystalline silicon (c-Si) solar cells, with the low cost of amorphous silicon technology. In this article, based on experimental data published by Sanyo, we simulate the performance of a series of HIT cells on N-type crystalline silicon substrates with hydrogenated amorphous silicon (a-Si:H) emitter layers, to gain insight into carrier transport and the general functioning of these devices. Both single and double HIT structures are modeled, beginning with the initial Sanyo cells having low open circuit voltages but high fill factors, right up to double HIT cells exhibiting record values for both parameters. The one-dimensional numerical modeling program “Amorphous Semiconductor Device Modeling Program” has been used for this purpose. We show that the simulations can correctly reproduce the electrical characteristics and temperature dependence for a set of devices with varying I-layer thickness. Under standard AM1.5 illumination, we show that the transport is dominated by the diffusion mechanism, similar to conventional P/N homojunction solar cells, and tunneling is not required to describe the performance of state-of-the art devices. Also modeling has been used to study the sensitivity of N-c-Si HIT solar cell performance to various parameters. We find that the solar cell output is particularly sensitive to the defect states on the surface of the c-Si wafer facing the emitter, to the indium tin oxide/P-a-Si:H front contact barrier height and to the band gap and activation energy of the P-a-Si:H emitter, while the I-a-Si:H layer is necessary to achieve both high Voc and fill factor, as it passivates the defects on the surface of the c-Si wafer. Finally, we describe in detail for most parameters how they affect current transport and cell properties.