Hydrogenated Microcrystalline Silicon Research Articles

Phosphorus doped hydrogenated silicon oxycarbide: Film formation, properties and its application on silicon heterojunction solar cell

An ultrathin phosphorus doped hydrogenated microcrystalline silicon oxycarbide (n-μc-SiCO:H) layer deposited by plasma enhanced chemical vapor deposition (PECVD) method can be used as a window layer for silicon heterojunction solar cells. The optical and electrical properties of n-μc-SiCO:H films were controlled by PECVD deposition conditions. The interplay effects of H2, CO2 and PH3 to SiH4 gas ratio on the chemical composition, material structure and properties of n-μc-SiCO:H film were systematically determined. O, H, C and P atoms were observed to incorporate into the silicon network of n-μc-SiCO:H layer, while most of the atoms bond directly to Si atoms. Incorporation of oxygen and carbon atoms into n-μc-SiCO:H film, confirmed by XPS as formation of Si-O and Si-C bonds, enlarged the optical absorption band gap (Eg) value. Both film crystallinity and phosphorus concentration in n-μc-SiCO:H layer were observed to be controlled by the H2, CO2 and PH3 to SiH4 gas ratio. The electric performance of HJT solar cell was depended on the optical and electrical properties of n-μc-SiCO:H layer. An average efficiency (across ∼ 120 cells) of 26.32 % was achieved in cells with optimized deposition parameters for the n-μc-SiCO:H layer. The reaction gas ratio was also the dominant factor in determining the number and size of nanoscale Si crystallites embedded in the n-μc-SiCO:H layer. The conductivity of n-μc-SiCO:H layer was determined by the activated phosphorus concentration but independent of the total phosphorus concentration. It was also found that large concentrations of small Si crystallites of size less than 3 nm improved film conductivity.

Comparative simulation analysis of μc Si:H and SnS BSF layers in CIGS solar cells

In this paper, we presented Cu(In1-xGax)Se2 (CIGS) based solar cells in which hydrogenated microcrystalline silicon (μc Si:H) and tin sulfide (SnS) are used as back surface field (BSF) layers. In CIGS thin film solar cell technology, thickness serves a crucial factor. Optimizing absorber thickness reduces the usage of scarce and expensive materials such as indium (In) and gallium (Ga) in CIGS cells. Integrating a heavily doped layer between the absorber and the back surface, known as the back surface field (BSF) layer, in solar cell design is a successful strategy for minimizing the thickness of the absorber layer. The suggested configuration utilizes μc-Si:H and SnS as the back surface field (BSF) layer. The buffer layer in this configuration employs less harmful InP instead of the typically utilized CdS layer. All the simulation work is performed using SCAP-1D simulation tool. The utilization of μc Si:H and SnS BSF layers yields optimized efficiencies of 31.51% and 31.01%, respectively. This simulation work demonstrates that use of a proper BSF layer is very effective not only in performance enhancement but also in reducing absorber material thickness.

The Impact of P-Type Layer on Performance and Stability of Thin Film Silicon Solar Cells in Relation to Third Generation: A review Analysis

Thin-film Silicon (Si) Solar Cells (SCs) have emerged as a promising candidate for next-generation photovoltaic devices due to their potential for cost-effectiveness and versatility. However, achieving high efficiency and long-term stability remains a significant challenge in their development. The primary challenges with thin-film Si SCs have been the poor infrared light absorption of Hydrogenated Microcrystalline Silicon (c-Si: H) and the light-induced metastability of Hydrogenated Amorphous Silicon (a-Si: H). This study reviewed the influence of the p-type layer, a key component in thin-film Si SCs, on both performance and stability. Third generation SCs are optimized for high Power Conversion Efficiency (PCE) at low manufacturing costs. According to the review of the comparison analysis, Patel K. et al., (2021) obtained the highest PCE of 30.17% with the a-Si/MoTe2 material (Photocurrent Density Jsc = 32.41mA/cm2, An Open-Circuit Voltage Voc = 1.093V, and Fill Factor (FF) = 85.12%) of the state-of-the-art previous works. The findings presented here contribute valuable insights toward the development of efficient and durable SC technology, crucial for advancing the adoption of renewable energy sources in our ever-growing energy demand.

Nanostructure and doping effects of a-Si:H and μc-Si:H anode in lithium-ion battery performance

The charge/discharge capacity and cycle performance of lithium-ion batteries (LIBs) are studied in terms of the nanostructure of silicon-based anode materials and doping. The anode material is chosen to be either hydrogenated amorphous silicon (a-Si:H) or hydrogenated microcrystalline silicon (μc-Si:H), in which the doping is controlled between non-doped intrinsic i-type and phosphorous-doped n-type. The results show that a LIB test cell composed of a n-type a-Si:H anode yields a higher performance. The specific capacity during discharge is obtained initially at 2478 mAh/g, 1940 mAh/g after 10 cycles, and 1360 mAh/g after 40 cycles under a 0.2C condition.

Effect of Large Uniaxial Stress on the Thermoelectric Properties of Microcrystalline Silicon Thin Films

This study reports on the behaviour of the thermoelectric properties of n- and p-type hydrogenated microcrystalline silicon thin films (µc-Si: H) as a function of applied uniaxial stress up to ±1.7%. µc-Si: H thin films were deposited via plasma enhanced chemical vapour deposition and thermoelectric properties were obtained through annealing at 200 °C (350 °C) for n-(p-) type samples, before the bending experiments. Tensile (compressive) stress was effective to increase the electrical conductivity of n-(p-) type samples. Likewise, stress induced changes in the Seebeck coefficient, however, showing an improvement only in electron-doped films under compressive stress. Overall, the addition of elevated temperature to the bending experiments resulted in a decrease in the mechanical stability of the films. These trends did not produce a significant enhancement of the overall thermoelectric power factor, rather it was largely preserved in all cases.

Simulation of Solar Cell Device Performance Based on Hydrogenated Microcrystal Silicon (µc-Si:H) With Finite Element Method (FEM)

The structure and thickness of the solar cell device layer have a big impact on how well the solar cell works. There for, the aim of this study was to examine how hydrogenated microcrystalline silicon solar cells’ thickness and device structure affected how well they work. Simulation or modeling of the structure in one dimension (1D) is used for the analysis. MATLAB programming was used to analyze the simulation result. The optical band gap changes due to the influence of the structure, therefore the thickness of the p-, I, and n layers are kept constant at 250 Å, 9000 Å, and 250 Å respectively. The results showed that the maximum performance is obtained at the optical band gap, Eci = 1,39 eV, and the resulting power is 0.063465 Watt. Whereas in the simulation of the effect of the thickness on the i-layer, the optical band gap is set to a constant value of Eci = 1,4 eV, while the thickness of the p-layer and n-layer is set to 250 Å. The results also indicate that the maximum performance is at the i-layer thickness of 9000 Å and the power generated is 0.063364 Watt.

Highly Microcrystalline Phosphorous‐Doped Si:H Very Thin Films Deposited by RF‐PECVD

Fine‐tuning the crystallinity and doping of the hydrogenated microcrystalline silicon thin films are the key points in obtaining high‐quality devices for above‐integrated circuit (above‐IC) image sensors. This study focuses on the structural and electrical properties of radio‐frequency plasma enhanced chemical vapor deposition (RF‐PECVD) deposited microcrystalline silicon (μc‐Si:H) contact layers. Herein, phosphorus‐doped μc‐Si:H is deposited by capacitively coupled plasma RF‐PECVD (13,56 MHz) from a SiH4 + H2 + PH3gas mixture with varying phosphine concentrations. The influence of phosphine concentration on dopant concentration, active dopant concentration, and crystallinity is studied by secondary ion mass spectrometry, Hall effect measurement, and Raman spectroscopy, respectively. A high doping level is attained, reaching up to 1.7 × 1020 cm−3. Furthermore, “low‐power” and “high‐power” deposition conditions are studied which lead to incubation layers of different nature.

Performance Enhancement of an a-Si:H/μc-Si:H Heterojunction p-i-n Solar Cell by Tuning the Device Parameters

In this work, the solar cell design parameters like- layer thickness, bandgap, donor and acceptor concentrations are varied to find optimum structure of a hydrogenated amorphous silicon (a-Si:H) and hydrogenated microcrystalline silicon (μc-Si:H) heterojunction p-i-n solar cell. A thin a-Si:H p-layer of 1 to 5 nm followed by a thick a-Si:H i-layer of thickness 1400 to 1600 nm and then thin n-layer of thickness 1 to 5 nm with acceptor concentration of 102 cm−3 and donor concentration of 1020 cm−3 and the bandgaps of p-, i-, and n- layers with higher bandgaps closer to 2.2 eV for a-Si:H p-layer, 1.85 eV for a-Si:H i-layer, and 1.2 eV for μc-Si:H n-layer have showed better performances. The optimum cell has a JSC of 18.93 mA/cm2, VOC of 1095 mV, Fill factor of 0.7124, and efficiency of 14.77%. The overall external quantum efficiency of the numerically designed cell also remained very high from 85-95 % for wavelengths of 300-650 nm range. This indicates that the device will perform its best under both high and low frequency i.e. ultra-violet, near visible and visible light wavelengths. Dhaka Univ. J. Sci. 69(2): 88-95, 2021 (July)

Comparative Study on the Quality of Microcrystalline and Epitaxial Silicon Films Produced by PECVD Using Identical SiF4 Based Process Conditions.

Hydrogenated microcrystalline silicon (µc-Si:H) and epitaxial silicon (epi-Si) films have been produced from SiF4, H2 and Ar mixtures by plasma enhanced chemical vapor deposition (PECVD) at 200 °C. Here, both films were produced using identical deposition conditions, to determine if the conditions for producing µc-Si with the largest crystalline fraction (XC), will also result in epi-Si films that encompass the best quality and largest crystalline silicon (c-Si) fraction. Both characteristics are of importance for the development of thin film transistors (TFTs), thin film solar cells and novel 3D devices since epi-Si films can be grown or etched in a selective manner. Therefore, we have distinguished that the H2/SiF4 ratio affects the XC of µc-Si, the c-Si fraction in epi-Si films, and the structure of the epi-Si/c-Si interface. Raman and UV-Vis ellipsometry were used to evaluate the crystalline volume fraction (Xc) and composition of the deposited layers, while the structure of the films were inspected by high resolution transmission electron microscopy (HRTEM). Notably, the conditions for producing µc-Si with the largest XC are different in comparison to the fabrication conditions of epi-Si films with the best quality and largest c-Si fraction.

Silicon Nanowire Solar Cells with μc‐Si:H Absorbers for Radial Junction Devices

Silicon nanowire (SiNW) radial junction (RJ) solar cells using hydrogenated microcrystalline silicon (μc‐Si:H) as absorber material have been studied. Since 2013, the performance of such RJ devices has been limited by the low fill factor (FF) and open‐circuit voltage (VOC). Thanks to the use of n‐type hydrogenated microcrystalline silicon oxide (μc‐SiOx:H) as a bottom doped layer, the authors developed μc‐Si:H RJ solar cells with a FF of 69.7% and a VOC of 0.41 V yielding a power conversion efficiency of 4.1%, which is more than 40% higher than the previously published efficiency record of 2.9%. Herein, the role of n‐type μc‐SiOx:H in the improvement of FF is highlighted.

Improving structural, optical, and electrical properties of μc-Si:H using non-uniform hydrogen dilution treatment on RF-PECVD prepared layers

Hydrogenated microcrystalline silicon (μc-Si:H) has been used in solar cell technology to improve solar conversion efficiency. In this work, the effects of some of the main preparation parameters of μc-Si:H have been studied. The μc-Si:H films were deposited in a standard RF-PECVD at the frequency of 13.56 MHz on glass and silicon substrates without any extra heat treatment. By changing the combination of silane (SiH4) and hydrogen (H2) in the deposition chamber, the proportion of crystalline silicon in the resulting film can be altered. The effects of hydrogen dilution ratio, defined as R=H2SiH4, on the structural, optical, and electrical properties of hydrogenated silicon, have been investigated. Two hydrogen dilution strategies have been used: uniform and non-uniform. The hydrogen dilution ratio was changed from 20 to 33, while other parameters such as RF power, deposition pressure, temperature, and time were remained constant at 30 W (power density of 300 mW/cm2), 0.3 Torr, 300 °C, and 60 min, respectively. Since increasing the number of hydrogen atoms during the deposition process can cause surface damage and consequently, the reduction of crystal growth, the effect of non-uniform dilution ratio has also been considered. The properties of the resulting hydrogenated microcrystalline silicon films were analyzed using X-ray diffraction (XRD), atomic force microscope (AFM), Raman spectroscopy, UV–Visible–near-infrared spectroscopy, and Fourier transform infrared (FTIR) spectroscopy etc. The maximum crystalline ratio of 61%, the crystallite size of 83.3 nm, the energy gap of 1.6 eV, the hydrogen content of 6.7%, and structural coefficient of 0.53, and the highest conductivity have been obtained for the hydrogenated microcrystalline silicon films prepared using the non-uniform dilution ratio of hydrogen. The lower energy gap of hydrogenated microcrystalline silicon with respect to that of the hydrogenated amorphous silicon, results in the absorption of a wider band of the solar spectrum and, therefore, higher efficiency of the related solar cells. In addition, the higher conductivity of hydrogenated microcrystalline silicon compared to that of the hydrogenated amorphous silicon, is of interest for application in photovoltaic and opto-electronic devices.

Reactive Force-Field Molecular Dynamics Study of SiGe Thin Film Growth in Plasma Enhanced Chemical Vapor Deposition Processes

SiGe thin films, such as hydrogenated amorphous silicon germanium (a-SiGe:H) and hydrogenated microcrystalline silicon germanium (μc-SiGe:H), are formed by plasma enhanced chemical vapor deposition (PECVD) methods from SiH4, GeH4, and H2. Thin film properties such as surface morphology, hydrogen content, and crystal structure are greatly affected by process parameters such as a substrate temperature, gas pressure, and gas composition. For example, SiH3 and GeH3 are dominant species when the SiGe thin film with low defect is deposited under low power density conditions. However, the structural defects are formed by SiH and SiH2 that are highly reactive species under high power density conditions. Although the density and flux of these highly reactive species are much lower than those of the dominant species, the electrical properties of the device are greatly affected by a few structural defects. Therefore, to understand the influence of the composition of each precursor on the thin film properties is important. The purpose of the present study is to clarify the influence of the composition of multiple precursors such as SiH3, GeH3, and H under different substrate temperatures on the surface morphology, hydrogen content, and crystal structure.We performed reactive force-field molecular dynamics (ReaxFF MD) simulations. An existing parameter set was modified to match the dissociation energies in gaseous species because bond formation and breaking are particularly important in this study. The substrate was Si (100)– (2×1), and the size of the simulation box was 30.72 Å× 26.88 Å× 45.00 Å. A periodic boundary condition was applied in the x and y directions, and a fixed boundary condition was applied in the z direction. The first bottom layer of the substrate was fixed to prevent vibrations of the substrate up and down. The second and third layers were controlled constantly at desired temperature by the Berendsen thermostat. The temperature was not controlled on the fourth and subsequent layers to prevent direct influences of changing the velocity of atom due to the temperature control on the surface reaction. The substrate temperature was set at 800 K, 1000 K, 1300 K, and 1600 K. 2000 SiH3 molecules with the velocity corresponding to 1300 K in the direction towards the substrate were deposited one by one onto the substrate surface every 7.5 ps. The initial position of the gaseous species was set at 10 Å above the top of substrate Si atoms, and the in-plane (x-y) position were set randomly. The Velocity-Verlet algorithm was used for time integrations corresponding to 0.25 fs time step. A pre-thermal annealing for 7.5 ps and a post-thermal annealing for 60 ps were performed before and after the deposition to fully equilibrate the substrate and deposited thin films.Figure shows front views of the final configurations and results of analysis when the substrate temperature is 800 K, 1000 K, 1300 K, and 1600 K. The yellow, blue, and red represent substrate Si atoms, added Si atoms, and added H atoms, respectively. Gray shown in the figure are gas-solid surfaces. The surface construction algorithm was used to calculate a surface area that is closely related to the surface morphology. The hydrogen content was calculated using the select type algorithm. The structure identification algorithm for the crystal structure was used to characterize the structure of simulated films. These analyses were carried out by the Open visualization tool (OVITO). The surface area decreases as the substrate temperature increases, indicating that the formation of smoother surface at high temperature. The diffusivity of a SiH3 molecule that reached to the surface increases as the substrate temperature increases, and the atomic scale valleys are filled. This tendency is in good agreement with relevant studies. The hydrogen content was calculated by dividing the number of added H atoms by the total number of atoms existing in the system. The hydrogen content decreases as the substrate temperature increases because a hydrogen desorption is promoted as the substrate temperature increases. Figure 1

Simulation and optimization of a-Si: H/μc-Si: H tandem solar cell with thinner active layers

In this study, the performances of a-Si: H(n-i-p) /μc-Si: H(n-i-p) tandem solar cell based on hydrogenated amorphous silicon (a-Si: H) and hydrogenated microcrystalline silicon (μc-Si: H) with thinner active layers were investigated by using numerical simulation. For simulation, a one-dimensional computer code AMPS-1D was used to investigat the effect of the top single cell n+ layer nature, the effect of the top single cell n+ μc-Si: H layer doping concentration (ND) and, the effect of the two active layers thicknesses, i-a-Si: H layer and i-μc-Si: H layer on the performances of the tandem cell. However, the merit figures, like J(V) characteristics at dark and under illumination, the electric fields, the energy band diagrams and, the cell output parameters are calculated and investigated.According to our calculations it is found that, by using a n+μc-Si: H layer with a doping concentration value ND = 1019 cm−3 instead of a n+ a-Si: H layer in the n-i-p top single cell the tandem solar cell performances were performed. It is also obtained, a values of 50 nm and 600 nm for the active layers i-a-Si: H and i-μc-Si: H thicknesses, respectively, are recommended for a-Si: H/μc-Si: H tandem solar cell good performances. Lastly, the tandem solar cell with top single cell n+μc-Si :H layer and with a thinner active layers thicknesses has the higher output parameters (JSC=10.52 mA/cm2, VOC=1414 mV, FF = 80.2 % and, the efficiency = 12.14 %).

Design and optimization of 26.3% efficient perovskite/FeSi2 monolithic tandem solar cell

A multijunction or tandem technique comprising a wide bandgap top cell and a narrow bandgap bottom cell may be a major stepping stone in an attempt to obtain high-efficiency solar cells. However, easier said than done, it takes a lot to correctly optimize the structure of all the involved layers so as to possibly obtain the desired results. In this paper, a perovskite (CH3NH3PbI3)/FeSi2 (p-i-n structure) 2-terminal (2-T) monolithic tandem solar cell is proposed and investigated using AFORS-HET v2.5 1D simulator. A hydrogenated amorphous silicon (a-Si:H)/hydrogenated microcrystalline silicon oxide (µc-Si1−xOx:H) tunnel recombination junction is employed to interconnect both perovskite and FeSi2 solar cell for current matching. The influence of both top and bottom absorber layer thickness is analyzed to optimize the device performance. The study reveals an optimized 26.3% efficient perovskite/FeSi2 monolithic tandem solar cell with JSC (21.4 mA cm−2), VOC (1.63 V), and FF (74.86%). The results in this paper suggest FeSi2 material with 0.87 eV bandgap as an alternative for narrow bandgap bottom cell for the perovskite-based tandem solar cells so as to obtain much higher efficiencies.

Phosphorus treatment to promote crystallinity of the microcrystalline silicon front contact layers for highly efficient heterojunction solar cells

The current loss is mainly due to the reflection and the parasitic absorption in the indium tin oxide (ITO) and amorphous silicon (a-Si:H) in the front side of silicon heterojunction (SHJ) solar cells. In this paper, we implemented n-type hydrogenated microcrystalline silicon oxide (n-μc-SiOx:H) as the front surface field (FSF) to improve the short-circuit current density (JSC) of SHJ solar cells. The advantage of employing n-μc-SiOx:H layer is due to its low optical absorption coefficient and tunable refractive index. However, the introduction of carbon dioxide increases light transmission but reduces the crystallinity of n-μc-SiOx:H layer. Meanwhile, inhibiting the incubation layer and increasing microcrystalline/amorphous mixture phase during the growth are critical to the solar cell performance. Therefore, we implemented a high phosphorus-doping seed layer to form a nucleation layer to improve the crystallinity of n-μc-SiOx:H layer. In addition, the plasma enhanced chemical vapor deposition (PECVD) process parameters of each layer were optimized to obtain good optical and electrical properties of n-μc-SiOx:H layer. Finally, a 242.5 cm2 solar cell had been fabricated with conversion efficiency of 23.87%, open-circuit voltage (VOC) of 739.8 mV, fill factor (FF) of 82.33% and JSC of 39.19 mA/cm2, which was 0.31 mA/cm2 higher than that of the conventional n type a-Si:H SHJ solar cells.

The effects of air, oxygen and water exposure on the sub-bandgap absorption, the electronic conductivity and the ambipolar diffusion length in highly crystalline microcrystalline silicon films for photovoltaic applications

Reversible and irreversible changes due to long term air and short term de-ionized water (DIW) or pure oxygen exposure were investigated in about 1 µm thick hydrogenated microcrystalline silicon (µc-Si:H) films deposited on rough glass substrates, thereby comparing highly crystalline with compact material. Time and temperature dependent dark conductivity, steady-state photoconductivity, the steady-state photocarrier grating and dual-beam photoconductivity methods have been used to study the effects. Standard measurement procedures defined previously have been carefully applied to record the changes after different treatments using the steady-state methods under light. After long term air exposure of highly crystalline µc-Si:H films, a thermal annealing step leads to an increase in dark conductivity (σD) and steady-state photoconductivity (σph) as well as to a significant increase in the sub-bandgap absorption. These effects are likely due to a reversible recovery from surface adsorbents in a porous microstructure after air exposure resulting in surface charge and Fermi level shifts in agreement with earlier results. Compact µc-Si:H films showed only marginal effects upon an annealing after long term air exposure suggesting much reduced susceptibility to surface adsorbent induced by Fermi level shifts. Five hours exposure to de-ionized water at 80 °C caused more than an order of magnitude increase in σD and σph and a substantial decrease in the sub-bandgap absorption spectrum in highly crystalline as well as in compact µc-Si:H films. In addition, minority carrier diffusion lengths measured by the steady-state photocarrier grating method improved significantly. The changes after exposure to water were not reversible upon our standard annealing procedure. Exposure to high purity oxygen gas at 150 °C resulted in similar effects like the exposure to DIW. Also here the changes in material properties were not reversible upon annealing. Results are discussed in terms of adsorption and chemical reactions on surfaces in the porous highly crystalline material versus the materials with more compact structures. Results are compared to earlier observations and consequences for device application will be indicated.

Pulse measurements of small area thin film μc-Si:H/ZnO:B photodiodes

We introduce a triggered optoelectronic system operating in a pulse mode in the near infrared and visible spectral range 0.75– eV. The system measures current-voltage (I-V) characteristics in dark and under visible light illumination as well as electroluminescence (EL) spectra of small area thin film photodiodes and light emitting diodes with size below 1 mm2. The usefulness of the setup is demonstrated by measurement of optoelectronic properties of a hydrogenated microcrystalline silicon μc-Si:H)p-i-n diode deposited on a semi-transparent nanostructured ZnO:B electrode. No s-shaped I-Vcharacteristics were observed under white illumination near an open circuit voltage Uoc indicating a negligible charge accumulation near μc-Si:H/ZnO:B interface. The weak infrared EL correlates with the current density.

Computer modeling of the front surface field layer on the performance of the rear-emitter silicon heterojunction solar cell with 25 % efficiency

Highly conductive materials with wide band gaps are used as front surface field (FSF) layer to achieve a prominent efficiency in silicon heterojunction (SHJ) solar cells. In this study, we demonstrate an n-type hydrogenated microcrystalline silicon oxide (μc-SiO:H) layer with high conductivity and beneficial optical properties for its application in SHJ solar cells. To develop a substitute to a-Si:H (n), we started our research in the synthesis of HIT-type solar cells with three different layers, namely, a-Si:H (n), micro-crystalline silicon (μc-Si: H(n)), and μc-SiO:H (n). Owing to its better surface passivation, wide optical gap, and high conductivity, the μc-SiO:H (n) layer was employed as a substitute to a-Si:H (n). It is difficult to thoroughly investigate the effects of every parameter, such as the thickness, the electron affinity, and the doping density on the device performance experimentally. We, therefore, used a program based on the automat for simulation of heterostructures (AFORS-HET), to evaluate the limitation of the conversion efficiency, which provides a convenient way to accurately evaluate the role of various parameters. We obtained a high efficiency with open circuit voltage, (VOC) of 755.3 mV and a fill factor (FF) of 79.82 % are essential factors owing to a favorable bending of the conduction band in the μc-SiO:H (n) next to the a-Si:H (i). We achieved a high efficiency of 25.35 % using a μc-SiO:H film with both an appropriate electron affinity of 4.1 eV and the doping density of 1019 cm−3.

Optimization of Transparent Passivating Contact for Crystalline Silicon Solar Cells

A highly transparent front contact layer system for crystalline silicon (c-Si) solar cells is investigated and optimized. This contact system consists of a wet-chemically grown silicon tunnel oxide, a hydrogenated microcrystalline silicon carbide [SiO2/µc-SiC:H( n )] prepared by hot-wire chemical vapor deposition (HWCVD), and a sputter-deposited indium doped tin oxide. Because of the exclusive use of very high bandgap materials, this system is more transparent for the solar light than state of the art amorphous (a-Si:H) or polycrystalline silicon contacts. By investigating the electrical conductivity of the µc-SiC:H( n ) and the influence of the hot-wire filament temperature on the contact properties, we find that the electrical conductivity of µc-SiC:H( n ) can be increased by 12 orders of magnitude to a maximum of 0.9 S/cm due to an increased doping density and crystallite size. This optimization of the electrical conductivity leads to a strong decrease in contact resistivity. Applying this SiO2/µc-SiC:H( n ) transparent passivating front side contact to crystalline solar cells with an a-Si:H/c-Si heterojunction back contact we achieve a maximum power conversion efficiency of 21.6% and a short-circuit current density of 39.6 mA/cm2. All devices show superior quantum efficiency in the short wavelength region compared to the reference cells with a-Si:H/c-Si heterojunction front contacts. Furthermore, these transparent passivating contacts operate without any post processing treatments, e.g., forming gas annealing or high-temperature recrystallization.

Effects of ratio of hydrogen flow on microstructure of hydrogenated microcrystalline silicon films deposited by magnetron sputtering at 100 °C

Hydrogenated microcrystalline silicon (µc-Si:H) films were prepared on glass and silicon substrates by radio frequency magnetron sputtering at 100 °C using a mixture of argon (Ar) and hydrogen (H2) gasses as precursor gas. The effects of the ratio of hydrogen flow (H2/(Ar+H2)%)) on the microstructure were evaluated. Results show that the microstructure, bonding structure, and surface morphology of the µc-Si:H films can be tailored based on the ratio of hydrogen flow. An amorphous to crystalline phase transition occurred when the ratio of hydrogen flow increased up to 50%. The crystallinity increased and tended to stabilize with the increase in ratio of hydrogen flow from 40% to 70%. The surface roughness of thin films increased, and total hydrogen content decreased as the ratio of hydrogen flow increased. All µc-Si:H films have a preferred (111) orientation, independent of the ratio of hydrogen flow. And the µc-Si:H films had a dense structure, which shows their excellent resistance to post-oxidation.