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In this article, solid state analysis of microcrystalline silicon tandem solar cell, c-Si/a-Si:H/µc-SiGe, performed to investigate the lack of the efficiency in quarter pyramid solar cells. The optical and electrical characterization is performed in FDTD software for 2D device characteristics analysis. After carried out the device characteristics, the efficiency of the microcrystalline silicon tandem solar cell with three different light trapping techniques is studied and compared with planar solar cell and with anti-light reflecting coatings (ITO and Si3N4). The outcome of this work shows that checkerboard light trapping design gives η = 12.40%. The increase in efficiency with Checker-board light trapping design is 20.5% as compared to the planar solar cell, 17.20% as compared to pyramidal technique, and 15.42% as compared to ITO and Si3N4. Using Quarter Pyramid and Empty Checker Design (QPEC) technique, the percent increase in efficiency is 9.20% compared to the planar solar cell and 3.3% increase as compared to ITO and Si3N4. With Pyramidal Design, light trapping increases and efficiency increases by 4.10% as compared to the planar solar cell and reduces by 2.17% as compared to ITO and Si3N4. The efficiencies for both ITO and Si3N4 antireflection coatings are both 10.48%. [ABSTRACT FROM AUTHOR]

In this work, we report on the deposition of microcrystalline silicon (µc-Si:H) films produced from silane (SiH4), hydrogen (H2), and argon (Ar) mixtures using the plasma-enhanced chemical vapor deposition (PECVD) technique at 200 °C. Particularly, we studied the effect of RF power on the crystalline fraction (XC) of the deposited films, and we have correlated the XC with their optical, electrical, and structural characteristics. Different types of characterization were performed in the µc-Si:H film series. We used several techniques, such as Raman scattering spectroscopy, Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM), among others. Our results show that RF power had a strong effect on the XC of the films, and there is an optimal value for producing films with the largest XC.

Boron doping level and boron activation in silicon thin films grown by PECVD under epitaxial (p+ epi‑Si) and microcrystalline (p+ µc-Si) conditions have been investigated as functions of the substrate material and annealing in the range of 200°C – 300°C. Hall effect measurements show that in the as-deposited state, the conductivity is mainly governed by the carrier concentration, while the hole mobility is controlled by the crystalline quality. SIMS measurements reveal that dark conductivity is not directly proportional to the boron doping level, nor to the presence of B-H complexes, suggesting that carbon contamination and the formation of B-O complexes could play an important role in the electrical properties of the material. Annealing in air resulted in an increase in the dark conductivity for all samples. However, the increase was much higher (up to two orders of magnitude) for the samples deposited on silicon-on-insulator (SOI) substrates which have better crystalline quality and displayed the highest increase in hole carrier concentration, related to boron activation. Thus, the substrate material influences both the crystalline quality and the boron incorporation in the p-type material. At high boron incorporation, the mobility limitations are likely to be due to carrier concentration rather than to the crystalline quality, indicating that p+ µc-Si conditions allow a conductivity advantage over p+ epi‑Si conditions due to a higher doping level, which makes them suitable as hole-selective contacts in solar cells.

In this work, we report on the deposition of microcrystalline silicon (µc-Si:H) films produced from silane (SiH4), hydrogen (H2), and argon (Ar) mixtures using the plasma-enhanced chemical vapor deposition (PECVD) technique at 200 °C. Particularly, we studied the effect of RF power on the crystalline fraction (XC) of the deposited films, and we have correlated the XC with their optical, electrical, and structural characteristics. Different types of characterization were performed in the µc-Si:H film series. We used several techniques, such as Raman scattering spectroscopy, Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM), among others. Our results show that RF power had a strong effect on the XC of the films, and there is an optimal value for producing films with the largest XC. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The degradation of two amorphous silicon‐based photovoltaic (PV) modules, namely, of single junction amorphous silicon (a‐Si) and of micromorph tandem (a‐Si/ μ‐Si), after 11 years of exposure in the south of Spain is analyzed. Their I‐V curves were measured outdoors to study the changes of the electrical parameters in the course of three different periods: during the initial days of exposure, during the first year, and in the subsequent 10‐year period. The translation of the curves to an identical set of operating conditions, which enables a meaningful comparison, was done by the different correction procedures described in the standard IEC60891:2021, including the procedure 3, which does not require the knowledge of module parameters, whose values are typically not available. The annual power degradation rates over the entire 11‐year period are 1.12% for the a‐Si module, which is 3.02% for the first year, and 0.98% for the a‐Si/ μ‐Si, which is 2.29% for the initial year. [ABSTRACT FROM AUTHOR]

The performance of four thin-film photovoltaic modules is analyzed after an initial stabilization period and a subsequent outdoor exposition. The seasonal variations and the degradation rates of a single-junction hydrogenated amorphous silicon (a-Si:H) module, a tandem amorphous microcrystalline Silicon (a-Si/ μ c-Si) module, a heterostructure cadmium sulfide-cadmium telluride (CdS/CdTe) module and a copper indium gallium selenide (CIGS) are examined and correlated to spectral changes. The I–V curves have been measured every 5 min; the electrical parameters and parasitic resistances have been identified. By exploiting a number of experimental measurements acquired within a narrow interval of irradiance and cell temperature, a novel mathematical model has been developed and fitted: it considers a stationary seasonal variation component and a linear long-term degradation component. The results show annual power degradation rates of 4.0% for the a-Si:H module, 3.4% for the a-Si/ μ c-Si and 3.5% for the CdS/CdTe, whereas for the CIGS module the annual degradation is not significant, i.e. 0.2%. [Display omitted] [ABSTRACT FROM AUTHOR]

A novel compact realization of the XNOR/ XOR function is demonstrated with multimodal transistors (MMTs). The multimodal thin-film transistors (MMT’s) structure allows efficient use of layout area in an implementation optimized for unipolar thin-film transistor (TFT) technologies, which may serve as a multipurpose element for conventional and emerging large-area electronics. Microcrystalline silicon device fabrication is complemented by physical simulations. [ABSTRACT FROM AUTHOR]

A waveguide-mode sensor detects changes in the complex refractive index on the surface of a planar waveguide chip with high sensitivity. We developed a waveguide-mode sensor chip with the Si/SiO2 structure. It was predicted from simulations that a third layer of high refractive index added to the outermost surface of the planar waveguide may improve the sensitivity of the waveguide-mode sensor. In this research, we designed and manufactured a borosilicate glass substrate chip with a Si/SiO2/SiOx structure via sputtering deposition, and we improved the sensitivity of the waveguide-mode sensor chip. The Si/SiO2/SiOx structure chip was approximately 1.5 times more sensitive to refractive index changes than the Si/SiO2 structure chip. [ABSTRACT FROM AUTHOR]

Abstract The intrinsic microcrystalline silicon thin films were deposited by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD). Two series of films with different deposition rate 0.30 nm/s and 1.94 nm/s were prepared. The film surface and gas phase reaction growth processes were monitored with real-time spectroscopic ellipsometry and optical emission spectroscopy. The effect of deposition rate on the microcrystalline silicon thin film growth mechanism has been studied. The microcrystalline silicon surface growth was analyzed with KPZ model. The results show that the growth exponent of β is 0.448 for the films with low deposition rate, and the growth exponent of β is 0.302 for the films with high deposition rate. The growth exponent does not increase with deposition rate, but declines. And the reasons for this phenomenon were explained. [ABSTRACT FROM AUTHOR]

The major issues of thin-film silicon solar cells have been the light-induced metastability of hydrogenated amorphous silicon (a-Si:H) and the weak infrared light absorption of hydrogenated microcrystalline silicon (μc-Si:H). In order to overcome these challenges, we have developed a novel deposition process for a-Si:H and an improved light trapping scheme for μc-Si:H light absorbers, leading to four record independently-confirmed conversion efficiencies with single-junction and multijunction device structures. In this article, we review some technological progresses that led to the notable improvement in thin-film silicon solar cells, and address some limitations imposed by the absorber layer quality as well as the cell design. [ABSTRACT FROM AUTHOR]

Tandem amorphous/microcrystalline silicon thin-film solar modules with large-area panels, high energy yield, low light-induced degradation, and high damp-heat reliability are commercially manufactured. Several novel technologies are researched, developed, and introduced into the production line. These include (1) special passivation to increase the shunt resistance by an order of magnitude and enhance modules' low-light performance; (2) large-area uniformity of transparent-conducting-oxide films and lamination processes to reduce the problem of cells' current and segments’ voltage mismatches; (3) segment laser scribing to enable the modules' output voltage to 70 V and 30 V; (4) novel front reflective layers to enable customized color appearance; and (5) special 4-step laser scribing to produce see-through modules of purple, dark blue, light blue, silver, golden, orange, red wine, and coffee colors. Two new types of modules: low-voltage modules and see-through color modules are successfully developed, manufactured, and installed. The performance ratio of a 900 kWp system of 30 V low-voltage modules has been simulated and projected to be 92.1%, which is 20% more than its crystalline silicon and CdTe counterparts. The see-through color modules have been achieved with the highest module power reaching 105 W and the highest visible-light transmittance near 20%. [ABSTRACT FROM AUTHOR]

Thermoelectric technology has not yet been able to reach full-scale market penetration partly because most commercial materials employed are scarce/costly, environmentally unfriendly and in addition provide low conversion efficiency. The necessity to tackle some of these hurdles leads us to investigate the suitability of n-type hydrogenated microcrystalline silicon (μc-Si: H) in the fabrication of thermoelectric devices, produced by plasma enhanced chemical vapour deposition (PECVD), which is a mature process of proven scalability. This study reports an approach to optimise the thermoelectric power factor (PF) by varying the dopant concentration by means of post-annealing without impacting film morphology, at least for temperatures below 550°C. Results show an improvement in PF of more than 80%, which is driven by a noticeable increase of carrier mobility and Seebeck coefficient in spite of a reduction in carrier concentration. A PF of 2.08 × 10−4 W/mK2 at room temperature is reported for n-type films of 1 μm thickness, which is in line with the best values reported in recent literature for similar structures. [ABSTRACT FROM AUTHOR]

An atmospheric-pressure plasma deposition system was developed and used to deposit intrinsic hydrogenated microcrystalline silicon (μc-Si:H) thin films for μc-Si:H thin film solar cells. The helium (He) gas concentration in plasma increased Raman crystallinity (X c ) of μc-Si:H, which was a critical parameter to determine photovoltaic performance. In addition, dependence of X c on the He concentration is shown to be closely related to the atomic hydrogen flux during film growth, which is evidenced by plasma diagnostics derived from in situ optical emission spectroscopy measurements. Those analysis contributed to achieve impressive photovoltaic performance – namely, a power conversion efficiency of 4.60%, an open-circuit voltage of 0.52 V, a short-circuit current density of 13.62 mA/cm 2 , and a fill factor of 0.65, which is the first experimental demonstration of μc-Si:H thin film solar cells fabricated with the atmospheric-pressure plasma deposition under very high working-pressure regime at 13.3 kPa. [ABSTRACT FROM AUTHOR]

Low-temperature growth of microcrystalline silicon (mc-Si) is attractive for many optoelectronic device applications. This paper reports a detailed comparison of optical properties, microstructure, and morphology of amorphous silicon (a-Si) thin films crystallized by furnace annealing and flash lamp annealing (FLA) at temperatures below the softening point of glass substrate. The initial a-Si films were grown by plasma enhanced chemical vapor deposition (PECVD). Reflectance measurement indicated characteristic peak in the UV region ~280 nm for the furnace annealed (>550 °C) and flash lamp annealed films, which provided evidence of crystallization. The film surface roughness increased with increasing the annealing temperature as well as after the flash lamp annealing. X-ray diffraction (XRD) measurement indicated that the as-deposited samples were purely amorphous and after furnace crystallization, the crystallites tended to align in one single direction (202) with uniform size that increased with the annealing temperature. On the other hand, the flash lamp crystalized films had randomly oriented crystallites with different sizes. Raman spectroscopy showed the crystalline volume fraction of 23.5%, 47.3%, and 61.3% for the samples annealed at 550 °C, 650 °C, and with flash lamp, respectively. The flash lamp annealed film was better crystallized with rougher surface compared to furnace annealed ones. [ABSTRACT FROM AUTHOR]

Abstract: Microcrystalline silicon thin‐film solar cells prepared on hexagonal tiled surfaces exhibit record short‐circuit current densities and energy conversion efficiencies. However, it remains unclear if hexagonal textured substrates represent the best possible substrate tiling. In this study, hexagonal tiled substrates are compared with square and triangular tiled substrates in terms of photon management and microstructure. The 3D interface morphology of the individual layers of the solar cells is calculated and used as input parameters for the prediction of microcracks in the film and the simulation of 3D optical wave propagation. A comparison of the calculated interface morphologies with experimental results exhibits a good agreement for solar cells on hexagonal textured substrates, permitting calculations for solar cells on square and triangular textured substrates. The investigation of the crack formation process indicates that the square and the triangular textured substrates are superior to the hexagonal textured substrates. Finally, crack‐free triangular textured solar cells exhibit increased short‐circuit current densities compared to hexagonal and square textured solar cells. [ABSTRACT FROM AUTHOR]

One challenge for microcrystalline silicon (μc-Si:H) deposition is to achieve high deposition rates while maintaining high quality films. In this work, an inductively-coupled plasma (ICP) is used to deposit μc-Si:H on glass substrates by means of a novel planar resonant antenna at 13.56 MHz. No particle formation occurs in the low pressure (5 Pa) plasma, but the films suffer post-oxidation. By embedding a 5 MHz RF-biased substrate, films deposited simultaneously with and without RF bias are compared. It is shown that large area, low pressure (5 Pa), particle-free ICP deposition at 1 nm/s of μc-Si:H films can be obtained without post-oxidation by means of a planar resonant antenna, provided that RF substrate bias is included for independent control of the ion energy. [ABSTRACT FROM AUTHOR]

In this paper, we present the characterization and modeling of the electrical transport of hydrogenated microcrystalline silicon (μc-Si:H). Electrical conductivity measurements for several crystalline fractions have been carried out. The latter have been combined with surface potential measurements from atomic force microscopy in order to investigate the electrical transport in the heterogeneous structure. We propose a new numerical model based on a three-dimensional electrical circuit to extract the parameters involved in the transport. A physical based model of tunneling at large grain boundary is implemented. Combining the latter with other conductivities in the large electrical circuit, the percolation behavior in respect to crystalline fraction is fully simulated. A benefit of such a model is that it captures the fundamental physics phenomena with only a few comprehensible parameters. [ABSTRACT FROM AUTHOR]

Surface-sensitive UV Raman spectroscopy is used to analyze the crystallinity of silicon films less than 20 nm thick directly on silicon wafers. The 325-nm excitation has a Raman detection thickness of only 13 nm within the silicon film, thus eliminating signal from the substrate. We demonstrate measured crystallinities of microcrystalline silicon thin films that are consistent with the microstructure observed in transmission electron microscopy. Comparison is also made to ellipsometry, which is less able to accurately determine crystallinity than UV Raman spectroscopy. The UV Raman approach is particularly useful for layers grown on substrates of the same material but with different microstructure, and can be extended to non-silicon materials. [ABSTRACT FROM AUTHOR]

We present Schottky junction solar cell composed of graphene transferred onto hydrogenated amorphous and microcrystalline silicon, a low-cost alternative to well-explored crystalline silicon. We demonstrated sample with open-circuit voltage of 445 mV, a remarkable value for undoped graphene-based solar cell. Photovoltaic characteristics of this sample remained stable over 11 months and could be further improved by doping. The graphene/silicon junctions were characterized by current-voltage curves obtained locally by conductive atomic force microscopy (C-AFM) and macroscopically by standard solar simulator. Very good correlation between both independent measurements proved C-AFM as highly useful tool for photovoltaic characterization on nano- and micrometer scale. [ABSTRACT FROM AUTHOR]

An approach that models the fabrication and enables the characterization of randomly self-textured silicon thin film solar cells is developed and are compared to experimental results. The optical and electrical properties of the solar cells depend on the morphology of the randomly self-textured substrate and the formation of the individual layers of the solar cell. The influence of the interface morphology on the optical and electrical properties is investigated by 3D morphological algorithms. The calculated interface morphologies are compared to measured surfaces, and used as input parameters to simulate the optical wave propagation and to determine the formation of regions with reduced order (cracks) in the solar cells. The calculations are compared to experimentally realized 1.1 µm thick microcrystalline silicon solar cells prepared on randomly self-textured substrates with high energy conversion efficiency of up to 9.4%. Guidelines for the optical and electronic optimization are provided. [ABSTRACT FROM AUTHOR]

The influence of triangular grating used as a light trapping structure on the optical wave propagation within thin-film microcrystalline silicon (µc-Si:H) solar cells is investigated. A finite difference time domain (FDTD) approach is used to rigorously solve the Maxwell's equations in three dimensions. We apply two parameters of mean surface roughness ( S a ) and slope ( k ) to define triangular structure and study their influence on the absorption of µc-Si:H. When S a and k are set to 400 nm and 1, respectively, a largest enhancement of absorption is achieved. The optimum short circuit photocurrent ( J sc ) of a 1-µm thick µc-Si:H solar cell made on such a textured substrate can reach 27.0 mA/cm 2 . The carrier generation rate in the µc-Si:H material is also rigorously analyzed. Finally, we identify some key optical losses in µc-Si:H solar cells and propose for further optimizing the device design. [ABSTRACT FROM AUTHOR]

The influence of working pressure and inter-electrode gap distance on the quality of microcrystalline silicon prepared by PECVD at 40 MHz in three different KAI™ reactors designs with inter-electrode gaps of 28 mm, 16 mm and 7 mm has been investigated. The microcrystalline devices were implemented and studied as bottom cells in MICROMORPH™ tandem modules or processed with an optical filter to simulate the absorption of a top cell on a module size of 1.43 m 2 . Increasing the working pressure from 250 Pa to 2000 Pa resulted in an improvement of the efficiency of 1% absolute due to improvement in the open circuit voltage V oc and the fill factor FF . The influence of the deposition rate on the quality of the intrinsic absorber layers has been investigated and optimized. An unconventional crystallinity profile throughout the intrinsic absorber layer has been developed to further improve either the current density J sc or V oc and FF . By controlling and tuning the Raman crystallinity a very high open circuit voltage V oc of >1.42 V in a tandem cell design in full size modules (1.43 m 2 ) could be realized. [ABSTRACT FROM AUTHOR]

We present the study of high efficiency single and multi-junction solar cells, focusing on the stability against degradation under illumination. In both single and multijunction solar cells, the thickness of the a-Si:H absorber layer was varied over a wide range up to 790 nm. While single junction a-Si:H solar cells show reduced stability against prolonged light illumination with an increase in layer thickness, themultijunction solar cells are significantly more stable. In these cells the total thickness of the a-Si:H absorber layers (first and second sub-cells) can be significantly increased up to 790 nm while keeping the degradation level low (below 13%) after 1000 hrs of light soaking. The possible origins of an improved stability against degradation are addressed in the paper. [ABSTRACT FROM AUTHOR]

Spectral responses above the unity at short wavelengths have not been yet reported in μc-Si:H based n-i-p devices illuminated with a red bias light. In solar cells this effect is known as the Complementary Photo-Gating Effect. After calibrating the input parameters of our computer code by matching experimental output device characteristics, the necessary conditions to predict these anomalous responses at short wavelengths were explored. In order to obtain SR higher than unity at short wavelengths in μc-Si:H n-i-p devices under red bias illumination a highly defective buffer layer must be present at the p/i interface. The short wavelength a.c. probe beam modulates the carrier concentration trapped at the gap states of the defective interface strengthen the electrical field in the intrinsic layer and weaken the electrical field inside the p-doped and p/i buffer layers. The short wavelength a.c. probe beam reduces the total recombination loss inside the intrinsic layer with respect to its counterpart under only red bias light illumination generating a net gain and spectral responses over unity. This phenomenon is predicted in devices with either high or low mobility (p)-layers, such as (p)-a-SiC:H and (p)-μc-Si:H respectively, that are not very efficiently doped with boron. Spectral responses higher than one are very sensitive to the electrical parameters of the p/i defective buffer such as mobility gap, thickness, density of defects, mobilities, capture cross sections of donor traps, and to the Boron density present in the p-layer and to the spectral content of the red bias light. [ABSTRACT FROM AUTHOR]

The phosphorus-doped microcrystalline silicon thin films were deposited by PECVD (Plasma-enhanced chemical vapor deposition), the activation energy of thin films were measured by activation energy testing equipment. The activation energy of samples with different doping concentration and different depositing temperature were studied. The results showed that: the activation energy of phosphorus-doped microcrystalline silicon thin films lesser than intrinsic films. The unit of activation energy is meV. Crystalline volume fractions have little influence on activation energy when thin films have a good crystalline volume fraction, impurity effect plays an important role on the conductivity. [ABSTRACT FROM AUTHOR]

In this paper, microcrystalline silicon layer is proposed to replace the amorphous silicon layer in the tunneling oxide passivated contact (TOPCon) solar cell. Both the microcrystalline silicon layer and amorphous silicon layer were deposited by plasma enhanced chemical vapor deposition on quartz substrate and analysed by Raman spectra. The effects of high temperature annealing of TOPCon samples were revealed by scanning electron microscope and dopant profiler. It was observed that, for amorphous silicon layer, high crystallization could be realized by annealing at high temperature, which tends to damage the silicon layer as well as the tunneling silicon oxide. The microcrystalline silicon layer deposited by reducing the silane concentration can achieve higher crystallization at annealing temperature as low as 600 °C. Low temperature annealing avoids the blistering of the silicon layer and the balling-up of the tunneling silicon oxide, resulting in improved passivation. Furthermore, the higher doping efficiency of microcrystalline layer enhanced the performance of TOPCon solar cells, which were investigated by simulation study. [ABSTRACT FROM AUTHOR]