N-type Microcrystalline Silicon Research Articles

High-Performance Amorphous Silicon Thin Film Solar Cells Prepared at 100 °C: Toward Flexible Building-Integrated Photovoltaics

For low-cost and lightweight polymer/plastic substrates in flexible building-integrated photovoltaic (BIPV) modules, low-temperature processing is essential. Amorphous silicon (a-Si:H) requires processing at a temperature of 200–250 °C by plasma-enhanced chemical vapor deposition to obtain satisfactory optoelectronic properties, which limits such substrates in terms of thermal budget. This study is focused on the fabrication of p–i–n-type a-Si:H solar cells at relatively low temperatures (100 °C). Intrinsic a-Si:H films with large optical gaps (1.83 eV) were prepared at 100 °C using a high hydrogen dilution ratio. In addition, p-type amorphous silicon oxide and n-type microcrystalline silicon oxide films with large optical gaps and suitable conductivities were prepared at 100 °C using a gas mixture containing the dopant B2H6 or PH3 and CO2. Finally, an a-Si:H p–i–n cell was fabricated at 100 °C; it exhibited an excellent power conversion efficiency of 9.0%, which was higher than those reported for a-Si:H thin film photovoltaics prepared at 100 °C. We believe that this study will open promising routes for the development of high-performance and flexible BIPVs.

Mechanical Microsensors for Pulse Measurement

Health parameters measurement is the focus of many researches because of their wide application area. Mechanical sensors have also many interests, especially if their sensitivity is enough high to measure small deformations. Their application can then address pulse measurement or muscle and tendons movements (fig. 1). Mechanical sensor are widely developed. Low temperature technologies allow to fabricate them on many types of substrates including flexible substrates. These sensors require the use of piezoresistive materials. We previously develop mechanical sensors based on microcrystalline silicon resistances. Microsensors are fabricated on 25 µm thick Kapton. The piezoresistive material is N-type doped microcrystalline silicon deposited by PECVD. The main problem of this thin substrate is the stress induced during the process that deforms and creates cracks in each layer (fig. 2). In order to avoid this phenomenon, various possibilities were studied, first using different structures with nitride silicon layers. A specific cleaning process was also defined and the design of a shadow mask that reduce the surface of the microcrystalline silicon deposit was proposed. The combination of the three methods made that our samples are flatten and the cracks practically disappear. Different designs were then studied in order to obtain a good sensitivity to deformation. Resistances are characterized under mechanical stresses. Their response to variable deformations was measured. In order to increase the sensitivity of the sensor, a specific electronic circuit is used, including a variable amplification of the measured signal (typically equal to 7). Sensors are placed on a thin layer which shape can be change with pressure variation. Several deformations can then be applied. Sensors are able to response to variable frequencies and different excitation waves like simple delta pulse or complicated signals like the ECG wave. The sensor response to deformation is studied with those different signals and at different frequencies (fig. 3). Several geometries are compared with the aim of obtaining the most sensitive design. The sensitivity to deformation as well as the response time are studied. This shows the feasibility and development of a highly sensitive system for small deformation measurements. Figure 1

Mechanical Microsensors for Pulse Measurement

This paper presents a low cost flexible sensor that has been characterized by a homemade circuit. The technological process of the sensor was carried out at low temperature (180 °C) allowing to fabricate them on many types of substrates including flexible. As piezoresistive materials, N-type doped microcrystalline silicon deposited by PECVD was used. In order to obtain a good sensitivity to deformation, different designs were studied. Sensors are able to response to variable frequencies and different excitation waves such as a simple delta pulse or complex signals like the ECG wave. Several geometries are compared with the aim of obtaining the most sensitive design. This shows the feasibility and development of a highly sensitive system for small deformation measurements.

Influence of N-type μc-SiOx:H intermediate reflector and top cell material properties on the electrical performance of “micromorph” tandem solar cells

Amorphous silicon (a-Si:H) / micro-crystalline silicon (μc-Si:H), "micromorph" tandem solar cells have been investigated using a detailed electrical - optical model. Although such a tandem has good light absorption over the entire visible spectrum, the a-Si:H top cell suffers from strong light-induced degradation (LID). To improve matters, we have replaced a-Si:H by hydrogenated polymorphous silicon (pm-Si:H), a nano-structured silicon thin film with lower LID than a-Si:H. But the latter’s low current carrying capacity necessitates a thicker top cell for current-matching, again leading to LID problems. The solution is to introduce a suitable intermediate reflector (IR) at the junction between the sub-cells, to concentrate light of the shorter visible wavelengths into the top cell. Here we assess the suitability of N-type micro-crystalline silicon oxide (μc-SiOx:H) as an IR. The sensitivity of the solar cell performance to the complex refractive index, thickness and texture of such a reflector is studied. We conclude that N-μc-SiOx:H does concentrate light into the top sub-cell, thus reducing its required thickness for current-matching. However the IR also reflects light right out of the device; so that the initial efficiency suffers. The advantage of such an IR is ultimately seen in the stabilized state since the LID of a thin top cell is low. We also find that for high stabilized efficiencies, the IR should be flat (having no texture of its own). Our study indicates that we may expect to reach 15% stable tandem micromorph efficiency.

Development of highly conducting n-type micro-crystalline silicon oxide thin film and its application in high efficiency amorphous silicon solar cell

Wide band gap and highly conducting n-type nano-crystalline silicon film can have multiple roles in thin film solar cell. We prepared phosphorus doped micro-crystalline silicon oxide films (n-μc-SiO:H) of varying crystalline volume fraction (Xc) and applied some of the selected films in device fabrication, so that it plays the roles of n-layer and back reflector in p-i-n type solar cells. It is generally understood that a higher hydrogen dilution is needed to prepare micro-crystalline silicon, but in case of the n-μc-SiO:H an optimized hydrogen dilution was found suitable for higher Xc. Observed Xc of these films mostly decreased with increased plasma power (for pressure<2.0Torr), increased gas pressure, flow rate of oxygen source gas and flow rates of PH3>0.08 sccm. In order to determine deposition conditions for optimized opto-electronic and structural characteristics of the n-μc-SiO:H film, the gas flow rates, plasma power, deposition pressure and substrate temperature were varied. In these films, the Xc, dark conductivity (σd) and activation energy (Ea) remained within the range of 0–50%, 3.5×10−10S/cm to 9.1S/cm and 0.71eV to 0.02eV, respectively. Low power (30W) and optimized flow rates of H2 (500 sccm), CO2 (5 sccm), PH3 (0.08 sccm) showed the best properties of the n-μc-SiO:H layers and an improved performance of a solar cell. The photovoltaic parameters of one of the cells were as follows, open circuit voltage (Voc), short circuit current density (Jsc), fill-factor (FF), and photovoltaic conversion efficiency (η) were 950mV, 15mA/cm2, 64.5% and 9.2% respectively.

Wide gap microcrystalline silicon carbide emitter for amorphous silicon oxide passivated heterojunction solar cells

Wide gap n-type microcrystalline silicon carbide [µc-SiC:H(n)] is highly suitable as window layer material for silicon heterojunction (SHJ) solar cells due to its high optical transparency combined with high electrical conductivity. However, the hot wire chemical vapor deposition (HWCVD) of highly crystalline µc-SiC:H(n) requires a high hydrogen radical density in the gas phase that gives rise to strong deterioration of the intrinsic amorphous silicon oxide [a-SiOx:H(i)] surface passivation. Introducing an n-type microcrystalline silicon oxide [µc-SiOx:H(n)] protection layer between the µc-SiC:H(n) and the a-SiOx:H(i) prevents the deterioration of the passivation by providing an etch resistance and by blocking the diffusion of hydrogen radicals. We fabricated solar cells with µc-SiC:H(n)/µc-SiOx:H(n)/a-SiOx:H(i) stack for the front side and varied the µc-SiOx:H(n) material properties by changing the microstructure of the µc-SiOx:H(n) to evaluate the potential of such stack implemented in SHJ solar cells and to identify the limiting parameters of the protection layer in the device. With this approach we achieved a maximum open circuit voltage of 677 mV and a maximum energy conversion efficiency of 18.9% for a planar solar cell.

A novel strategy for preparing a selective back surface field of n-type emitter wrap through solar cells

In the present study, we have developed a novel mixed co-diffusion (MCD) process by which to prepare a selective back surface field (BSF) of n-type emitter wrap through (EWT) solar cells, which combines a plasma enhanced chemical vapor deposition (PECVD) phosphorus-doped n-type microcrystalline silicon as the dopant source, with a low temperature thermal oxidation (LTO) process. Through comparison between our MCD process and a standard co-diffusion (SCD) process, a BSF with a shallow doping depth of 0.56µm and high doping concentration of 1.9×1020at/cm3 is easily obtained by the MCD process under the low temperature of 750℃. Therefore, the MCD process is shown to reduce the number of high temperature processes, which cannot produce dopant redistribution, and can accurately control the doping concentrations and depths of the BSF and emitter. In addition, the novel method also eliminates the boron-rich layer, which induces misfit dislocations and bulk lifetime degradation, without extra chemical treatment. Therefore, the MCD process' open circuit voltage, short circuit current density, conversion efficiency and fill factor of the solar cells are respectively increased by 7mV, 6mA/cm2, 2% and 2%. These results indicate that the MCD process is a novel and potential agent for the SCD process.

Role of oxygen and nitrogen in n-type microcrystalline silicon carbide grown by hot wire chemical vapor deposition

N-type microcrystalline silicon carbide (μc-SiC:H(n)) deposited by hot wire chemical vapor deposition provides advantageous opto-electronic properties for window layer material in silicon-based thin-film solar cells and silicon heterojunction solar cells. So far, it is known that the dark conductivity (σd) increases with the increase in the crystallinity of μc-SiC:H(n)films. However, due to the fact that no active doping source is used, the mechanism of electrical transport in these films is still under debate. It is suggested that unintentional doping by atmospheric oxygen (O) or nitrogen (N) contamination plays an important role in the electrical transport. To investigate the impact of O and N, we incorporated O and N in μc-SiC:H(n) films and compared the influence on the microstructural, electronic, and optical properties. We discovered that, in addition to increasing the crystallinity, it is also possible to increase the σd by several orders of magnitude by increasing the O-concentration or the N-concentration in the films. Combining a high concentration of O and N, along with a high crystallinity in the film, we optimized the σd to a maximum of 5 S/cm.

New insight into the microstructure and doping of unintentionally n-type microcrystalline silicon carbide

Microcrystalline silicon carbide (μc-SiC:H) deposited by hot wire chemical vapor deposition (HWCVD) and plasma-enhanced chemical vapor deposition (PECVD) provide advantageous opto-electronic properties, making it attractive as a window layer material in silicon thin-film and silicon heterojunction solar cells. However, it is still not clear which electrical transport mechanisms yield dark conductivities up to 10−3 S/cm without the active use of any doping gas and how the transport mechanisms are related to the morphology of μc-SiC:H. To investigate these open questions systematically, we investigated HWCVD and PECVD grown layers that provide a very extensive range of dark conductivity values from 10−12 S/cm to 10−3 S/cm. We found out by secondary ion mass spectrometry measurements that no direct correlation exists between oxygen or nitrogen concentrations and high dark conductivity σd, high charge carrier density n, and low activation energy Ea. Higher σd seems to rise from lower hydrogen concentrations or/and larger coherent domain sizes LSiC. On the one hand, the decrease of σd with increasing hydrogen concentration might be due to the inactivation of donors by hydrogen passivation that gives rise to decreased n. On the other hand, qualitatively consistent with the Seto model, the lower σd and lower n might be caused by smaller LSiC, since the fraction of depleted grain boundaries with higher Ea increases accordingly.

Microcrystalline silicon: Strain gauge and sensor arrays on flexible substrate for the measurement of high deformations

This paper presents strain sensor arrays on flexible substrates able to measure local deformation induced by radii of curvature of few millimeters. Sensors use n-type doped microcrystalline silicon (μc-Si) as piezoresistive material, directly deposited on polyimide sheets at 165°C. Sensitivity of individual sensors was investigated under tensile and compressive bending at various radii of curvature, down to 5mm. A Transmission Line Method was used to extract the resistivity for each radius. The devices exhibited longitudinal gauge factors of −31 and longitudinal piezoresistive coefficients of −4.10−10Pa−1. Reliability was demonstrated with almost unchanged resistances after cycles of bending (standard deviation of 1.7%). Strain gauge arrays, composed of 800 resistors on a 2cm2 area, were fabricated with a spatial resolution of 500×500μm2. Strain mapping showed the possibility to detect local deformation on a single resistor or to detect larger objects. These strain sensor arrays can find applications when high sensitivity and high spatial resolution is required. This paper also showed that μc-Si can be a relevant semi-conductor candidate for flexible electronics.

Application of n-type microcrystalline silicon oxide as back reflector of crystalline silicon heterojunction solar cells

We investigated the application of n-type hydrogenated microcrystalline silicon oxide (n-µc-Si1−xOx:H) as an alternative back reflector material for n-type heterojunction solar cells. The effect of the CO2 and PH3 flow rates on the refractive index, oxygen content, conductivity, and crystalline fraction (Xc) of n-µc-Si1−xOx:H films was evaluated. By controlling the film oxygen content, the refractive index could be widely changed, while the absorption coefficient at wavelengths exceeding 800 nm was practically zero. We found that the insertion of an n-µc-Si1−xOx:H layer between the back surface field and the rear electrode improves the reflectance at long wavelengths. The improvement in reflectance resulted in higher internal quantum efficiency in the IR range, suggesting that the application of n-µc-Si1−xOx:H as a back reflector is promising for reducing long-wavelength losses in heterojunction solar cells.

Behavior of the parameters of microcrystalline silicon TFTs under mechanical strain

N-type and P-type microcrystalline silicon top-gate TFTs, processed directly on PEN plastic substrate at maximum temperature of 180°C, were mechanically stressed.These TFTs were bent by different curvature radii varying between infinite (flat) and 0.5cm. The tensile stress increases the electron mobility and the compressive stress decreases it. The tensile stress decreases the threshold voltage of N-type TFTs while the compressive stress increases it. These trends are inversed if the type of stress changes OR the type of TFTs changes.The total behavior under mechanical stress is exactly similar to that of single crystalline silicon MOSFETs in nano-scale technologies (90, 65, 45, 32nm), where nano-scale stress is introduced in the goal to engineer the electrical parameters. The similarity originates from the microcrystalline silicon active layer that behaves like single crystalline silicon even if the stress effects are softened by the grain boundaries and the multiple crystalline orientations of the grains.

Low-refractive-index and high-transmittance silicon oxide with a mixed phase of n-type microcrystalline silicon as intermediate reflector layers for tandem solar cells

Low-refractive-index and high-transmittance silicon oxide (SiOx) with a mixed phase of n-type microcrystalline silicon was developed for intermediate reflector layers (IRLs) of high-efficiency amorphous Si and microcrystalline-Si tandem solar cells. The refractive index, crystalline fraction, and conductivity of the SiOx IRLs were characterized as functions of the deposition conditions. The SiOx films were prepared by plasma-enhanced chemical vapor deposition, at a high pressure of 9Torr and high hydrogen dilution ratio of 400, and using a narrow electrode gap of 12mm. The films showed a refractive index of 1.85, crystalline fraction of ~50%, and conductivity of ~10−7S/cm. Furthermore, the transmittance of the films was more than 90% at wavelengths between 600nm and 1100nm. We present here the procedure to optimize the SiOx IRLs, which is to compare the changes in the top and bottom cells' current densities of the tandem solar cells fabricated with 10–20% thinner absorption layers. A stabilized efficiency of 11.12% and light-induced degradation of −9.3% could be achieved in a tandem module containing an optimized IRL by enhancing the top cell current. The SiOx IRLs developed and the optimization procedure discussed in this paper can be very useful for the fabrication of high-efficiency thin-film Si tandem modules.

μc-Si thin film transistors with very thin active layer

N-type microcrystalline silicon (μc-Si) top-gate Thin Film Transistors (TFTs) are fabricated at a maximum temperature of 180°C using different thicknesses of undoped μc-Si active layers. The effect of the thickness on the TFT performance is experimentally studied and then modeled using Silvaco software tools. The experimental high improvement of the subthreshold swing and the limitation of the rear channel effect, when using very thin active layer, are shown to be due to the increase of the lateral electrical field between the source or drain and the active layer. This increase of the lateral field is shown to be much more important for defected active layer as the microcrystalline silicon one compared to single crystalline silicon active layer. The importance of the use of very thin active layer for amorphous or ploy–micro–nano-crystalline silicon based TFTs is then demonstrated.

Remarkable progress in thin-film silicon solar cells using high-efficiency triple-junction technology

Despite the many advantages of thin-film silicon (Si) solar cells, their low efficiencies remain a challenge that must be overcome. Efficient light utilization across the solar spectrum is required to achieve efficiencies over 15%, allowing them to be competitive with other solar cell technologies. To produce high-efficiency thin-film Si solar cells, we have developed triple-junction solar cell structures to enhance solar spectrum utilization. To maximize the light management, in-house ZnO:Al layers with high haze ratios and high transmittances were developed. In addition, novel doping layers, such as n-type microcrystalline silicon oxide (µc-SiOx:H), which has a very low refractive index, and p-type microcrystalline silicon oxide (µc-SiOx:H), which has a wide bandgap, were successfully applied to the optical reflector and the window layer, respectively. Thin-film quality control techniques for the deposition of hydrogenated amorphous silicon (a-Si:H) in the top cell, hydrogenated amorphous silicon-germanium (a-SiGe:H) or hydrogenated microcrystalline silicon (μc-Si:H) in the middle cell, and hydrogenated microcrystalline silicon (μc-Si:H) in the bottom cell were also important factors leading to the production of high-efficiency triple-junction solar cells. As a result of this work, an initial efficiency of 16.1% (in-house measurement) in the a-Si:H/a-SiGe:H/μc-Si:H stack and a stabilized efficiency of 13.4% (confirmed by NREL) in the a-Si:H/μc-Si:H/μc-Si:H stack were successfully achieved in a small-area triple-junction solar cell with dimensions of 1cm×1cm.

N-Type microcrystalline silicon oxide layer and its application to high-performance back reflectors in thin-film silicon solar cells

Light trapping is a key issue in improving the efficiency of thin-film Si solar cells, and using a back reflector material plays a critical role in improving a cell's light-trapping efficiency. In this study, we developed n-type microcrystalline silicon oxide (n-μc-SiOx) films that are suitable for use as back reflectors in thin-film silicon solar cells. They exhibit a lower refractive index and lower absorption spectra, especially at long wavelengths of >700 nm, than conventional ZnO:Al materials, which are beneficial for this application. The n-μc-SiOx films were prepared by the PECVD (plasma-enhanced chemical vapor deposition) method and applied to the fabrication of back reflectors in μc-Si:H solar cells. We also characterized the changes in cell performance with respect to the refractive index, conductivity, and thickness of the n-μc-SiOx back reflectors. The novel back reflector boosts the total current density by up to 3.0% with the help of the enhanced long-wavelength response. It also improves open circuit voltage (Voc) and fill factor (FF), which may be attributed to the reduced shunt current caused by the anisotropic electrical characteristics of the n-μc-SiOx layer. Finally, we could achieve a conversion efficiency for the hydrogenated microcrystalline silicon (μc-Si:H) solar cells of up to 9.3% (Voc: 0.501 V, Jsc: 27.4 mA/cm2, FF: 0.68) using the n-μc-SiOx back reflector.

Local photovoltaic characterization for silicon thin film solar cells using a scanning probe microscope

The photovoltaic characterization of silicon thin film solar cells with nano-scale spatial resolution is demonstrated by a new characterization method developed using a scanning microscope. In the surface topography of p-i-n type amorphous silicon thin film solar cells, large and small convex grains corresponding to the textured surface of an Asahi U-type substrate and the crystalline grains in the n-type microcrystalline silicon layer are found. In the local photo-current image, distribution in local photo-current correlated with the structure of the n-type microcrystalline silicon layer is observed in the p-i-n type amorphous silicon (a-Si:H) thin film solar cells. The local surface potential in amorphous silicon thin film solar cells with light irradiation is also evaluated. In the local surface potential image of the p-i-n a-Si:H thin film solar cells without light irradiation, the local surface potential on the large convex grains found in the surface topography is smaller than that in the concave region between the large convex grains. Similar distribution of the local surface potential is observed in the local surface potential images with light irradiation. The local surface potential difference between the large convex grains and the concave region decreases with increasing power of the irradiation light.

Enhancing performance of amorphous SiGe single junction solar cells by post-deposition thermal annealing

In this work, amorphous silicon-germanium (a-SiGe:H) p-i-n single junction solar cells are fabricated using a 40MHz plasma-enhanced chemical vapor deposition system. Their s-curve characteristics were observed by current density-voltage measurements. Thermal annealing of cells at 150 °C in a vacuum effectively overcame the s-curve behavior. Additionally, comparing the external quantum efficiency spectra of annealed samples with those of as-deposited samples revealed that the spectral response of annealed cells was higher in the long wavelength range (600~900nm). Raman spectroscopy and electrical conductivity analyses revealed that the n-type microcrystalline silicon (n-μc-Si:H) layers of as-deposited cells were not optimal. Experimental results indicate that the i/n barrier heights of the as-deposited and annealed samples were 0.31eV and 0.20eV , respectively. The high energy barrier implies that the bad collection ability of charge carriers near the i/n interfaces of solar cells. An energy conversion efficiency of 6.38% was achieved after post-deposition annealing. The improvement in efficiency is concluded to have been caused largely by retention of n-μc-Si:H layers of high crystallinity and electrical conductivity after annealing.

Microcrystalline-Silicon-Oxide-Based N-Type Reflector Structure in Micromorph Tandem Solar Cells

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Transmission electron microscopy (TEM) results show that microstructures of n-<svg style="vertical-align:-2.29482pt;width:9.6374998px;" id="M10" height="9.6750002" version="1.1" viewBox="0 0 9.6374998 9.6750002" width="9.6374998" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(1.25,0,0,-1.25,0,9.675)"> <g transform="translate(72,-64.26)"> <text transform="matrix(1,0,0,-1,-71.95,66.6)"> <tspan style="font-size: 12.50px; " x="0" y="0">𝜇</tspan> </text> </g> </g> </svg>c-<svg style="vertical-align:-3.21404pt;width:31.0875px;" id="M11" height="14.8" version="1.1" viewBox="0 0 31.0875 14.8" width="31.0875" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(1.25,0,0,-1.25,0,14.8)"> <g transform="translate(72,-60.16)"> <text transform="matrix(1,0,0,-1,-71.95,63.41)"> <tspan style="font-size: 12.50px; " x="0" y="0">S</tspan> <tspan style="font-size: 12.50px; " x="6.9516678" y="0">i</tspan> <tspan style="font-size: 12.50px; " x="10.427502" y="0">O</tspan> </text> <text transform="matrix(1,0,0,-1,-52.5,60.28)"> <tspan style="font-size: 8.75px; " x="0" y="0">𝑥</tspan> </text> </g> </g> </svg>:H thin films contain nanocrystalline Si particles, which are randomly embedded in the a-<svg style="vertical-align:-3.21404pt;width:31.0875px;" id="M12" height="14.8" version="1.1" viewBox="0 0 31.0875 14.8" width="31.0875" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(1.25,0,0,-1.25,0,14.8)"> <g transform="translate(72,-60.16)"> <text transform="matrix(1,0,0,-1,-71.95,63.41)"> <tspan style="font-size: 12.50px; " x="0" y="0">S</tspan> <tspan style="font-size: 12.50px; " x="6.9516678" y="0">i</tspan> <tspan style="font-size: 12.50px; " x="10.427502" y="0">O</tspan> </text> <text transform="matrix(1,0,0,-1,-52.5,60.28)"> <tspan style="font-size: 8.75px; " x="0" y="0">𝑥</tspan> </text> </g> </g> </svg> matrix. This specific microstructure provides n-<svg style="vertical-align:-2.29482pt;width:9.6374998px;" id="M13" height="9.6750002" version="1.1" viewBox="0 0 9.6374998 9.6750002" width="9.6374998" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(1.25,0,0,-1.25,0,9.675)"> <g transform="translate(72,-64.26)"> <text transform="matrix(1,0,0,-1,-71.95,66.6)"> <tspan style="font-size: 12.50px; " x="0" y="0">𝜇</tspan> </text> </g> </g> </svg>c-<svg style="vertical-align:-3.21404pt;width:31.0875px;" id="M14" height="14.8" version="1.1" viewBox="0 0 31.0875 14.8" width="31.0875" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(1.25,0,0,-1.25,0,14.8)"> <g transform="translate(72,-60.16)"> <text transform="matrix(1,0,0,-1,-71.95,63.41)"> <tspan style="font-size: 12.50px; " x="0" y="0">S</tspan> <tspan style="font-size: 12.50px; " x="6.9516678" y="0">i</tspan> <tspan style="font-size: 12.50px; " x="10.427502" y="0">O</tspan> </text> <text transform="matrix(1,0,0,-1,-52.5,60.28)"> <tspan style="font-size: 8.75px; " x="0" y="0">𝑥</tspan> </text> </g> </g> </svg>:H thin films excellent optoelectronic properties; therefore, n-<svg style="vertical-align:-2.29482pt;width:9.6374998px;" id="M15" height="9.6750002" version="1.1" viewBox="0 0 9.6374998 9.6750002" width="9.6374998" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(1.25,0,0,-1.25,0,9.675)"> <g transform="translate(72,-64.26)"> <text transform="matrix(1,0,0,-1,-71.95,66.6)"> <tspan style="font-size: 12.50px; " x="0" y="0">𝜇</tspan> </text> </g> </g> </svg>c-<svg style="vertical-align:-3.21404pt;width:31.0875px;" id="M16" height="14.8" version="1.1" viewBox="0 0 31.0875 14.8" width="31.0875" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(1.25,0,0,-1.25,0,14.8)"> <g transform="translate(72,-60.16)"> <text transform="matrix(1,0,0,-1,-71.95,63.41)"> <tspan style="font-size: 12.50px; " x="0" y="0">S</tspan> <tspan style="font-size: 12.50px; " x="6.9516678" y="0">i</tspan> <tspan style="font-size: 12.50px; " x="10.427502" y="0">O</tspan> </text> <text transform="matrix(1,0,0,-1,-52.5,60.28)"> <tspan style="font-size: 8.75px; " x="0" y="0">𝑥</tspan> </text> </g> </g> </svg>:H thin films are appropriate candidates for &#x201c;<i >n-type reflector</i>&#x201d; structures in Si tandem solar cells.

A simulation study of thin film tandem solar cells with a nanoplate absorber bottom cell

A tandem thin film solar cell with a nanoplate absorber bottom cell that can solve the trade-off between light absorption and carrier transport in thin film solar cell is investigated. This structure has an n-type microcrystalline silicon nanoplate array on the substrate, and the p- and i-layers are sequentially grown along the surface of each n-type microcrystalline silicon nanoplate for bottom cell. After above bottom cell is fabricated, a similar process is used to fabricate an amorphous Si p–i–n top cell. High-aspect-ratio width/height nanoplates allow for the use of a material with sufficient thickness to obtain good optical absorption while simultaneously providing short collection lengths for excited carriers perpendicular to light absorption. The power conversion efficiency of nanoplate solar cells with 15,000nm plate height is around 10%, which is an approximately 40% enhancement over a planar solar cell with a similar layer stack.