Hydrogenated Microcrystalline Silicon Solar Cells Research Articles

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.

Thin-film microcrystalline silicon solar cells: 11.9% efficiency and beyond

High-efficiency thin-film hydrogenated microcrystalline silicon solar cells (µc-Si:H) were developed using a periodically textured substrate at a relatively high growth rate of ∼1 nm s−1. A record efficiency of 11.9% was independently confirmed in a µc-Si:H cell with an absorber thickness of approximately 2 µm. An improvement in fill factor contributed largely to realizing the record efficiency. The potential for further efficiency improvements was examined on the basis of suns–VOC measurement, indicating that an efficiency of 12.5% is practically achievable.

Integration of Light Trapping Silver Nanostructures in Hydrogenated Microcrystalline Silicon Solar Cells by Transfer Printing.

One of the potential applications of metal nanostructures is light trapping in solar cells, where unique optical properties of nanosized metals, commonly known as plasmonic effects, play an important role. Research in this field has, however, been impeded owing to the difficulty of fabricating devices containing the desired functional metal nanostructures. In order to provide a viable strategy to this issue, we herein show a transfer printing-based approach that allows the quick and low-cost integration of designed metal nanostructures with a variety of device architectures, including solar cells. Nanopillar poly(dimethylsiloxane) (PDMS) stamps were fabricated from a commercially available nanohole plastic film as a master mold. On this nanopatterned PDMS stamps, Ag films were deposited, which were then transfer-printed onto block copolymer (binding layer)-coated hydrogenated microcrystalline Si (µc-Si:H) surface to afford ordered Ag nanodisk structures. It was confirmed that the resulting Ag nanodisk-incorporated µc-Si:H solar cells show higher performances compared to a cell without the transfer-printed Ag nanodisks, thanks to plasmonic light trapping effect derived from the Ag nanodisks. Because of the simplicity and versatility, further device application would also be feasible thorough this approach.

Integration of Light Trapping Silver Nanostructures in Hydrogenated Microcrystalline Silicon Solar Cells by Transfer Printing

One of the potential applications of metal nanostructures is light trapping in solar cells, where unique optical properties of nanosized metals, commonly known as plasmonic effects, play an important role. Research in this field has, however, been impeded owing to the difficulty of fabricating devices containing the desired functional metal nanostructures. In order to provide a viable strategy to this issue, we herein show a transfer printing-based approach that allows the quick and low-cost integration of designed metal nanostructures with a variety of device architectures, including solar cells. Nanopillar poly(dimethylsiloxane) (PDMS) stamps were fabricated from a commercially available nanohole plastic film as a master mold. On this nanopatterned PDMS stamps, Ag films were deposited, which were then transfer-printed onto block copolymer (binding layer)-coated hydrogenated microcrystalline Si (µc-Si:H) surface to afford ordered Ag nanodisk structures. It was confirmed that the resulting Ag nanodisk-incorporated µc-Si:H solar cells show higher performances compared to a cell without the transfer-printed Ag nanodisks, thanks to plasmonic light trapping effect derived from the Ag nanodisks. Because of the simplicity and versatility, further device application would also be feasible thorough this approach.

Mechanism insight into the effect of I/P buffer layer on the performance of NIP-type hydrogenated microcrystalline silicon solar cells

A simulation and experimental study on the effect of the buffer layer at the I/P interface on the performance of NIP-type hydrogenated microcrystalline silicon (μc-Si:H) single-junction solar cells is presented. Device-quality hydrogenated amorphous silicon (a-Si:H) material as a buffer layer at the I/P interface obviously improves the performance of NIP-type μc-Si:H single-junction solar cells. In addition to the well-known mechanism that an a-Si:H I/P buffer layer can reduce the recombination current density at I/P interfaces, the optically and electrically calibrated simulations and supporting experimental results in this study illustrate that the performance improvement also originates from the mitigation of the electric screening effect due to the reduced defect density at the I/P interfaces, which reinforces the bulk electric field. Integrating an optimized hydrogen profiling strategy and adding a-Si:H I/P buffer layer yielded an initial efficiency of 9.20% for μc-Si:H single-junction solar cells with an active area of 0.27 cm2. This study may provide new ideas of further improving the performance of NIP-type μc-Si:H single-junction solar cells by mitigating the electric screening effect.

Effect of I/N interface on the performance of superstrate hydrogenated microcrystalline silicon solar cells

A study on the effect of the n-type hydrogenated amorphous silicon (a-Si:H) buffer layers at the I/N interfaces on the overall performance of superstrate (pin-type) hydrogenated microcrystalline silicon (μc-Si:H) single-junction solar cells with wide band gap silicon oxide doped supporting layers is presented. By integrating the n-type a-Si:H materials with proper band gap and thickness values at the I/N interface, the band gap discontinuity between the μc-Si:H intrinsic and n-type nc-SiOx:H layers can be successfully compensated for, thereby improving the carrier collection, reducing the accumulation and recombination of photo-generated carriers near the I/N interface, and improving the overall current and power output of the μc-Si:H cells. Further adoption of an optimized hydrogen profiling technique based on the optimized n-type a-Si:H buffer layers yields an initial conversion efficiency of 10.05% for μc-Si:H single-junction solar cells with a thickness of 2μm.

Transfer-printed silver nanodisks for plasmonic light trapping in hydrogenated microcrystalline silicon solar cells

Plasmonic light trapping is a topic of high interest, but research regarding this topic has been so far impeded owing to the lack of convenient methods to produce desired metal nanostructures in solar cells. To overcome this challenge, we herein introduced a transfer printing approach and performed demonstrative light trapping. Promising results were verified with superstrate-type hydrogenated microcrystalline Si cells fabricated on flat superstrates; for example, the photocurrent generated in the 650–1100 nm range increased to up to 60%. Since our transfer printing approach was applicable to textured surfaces, the integration of plasmon-mediated light trapping and front texture-mediated light trapping was also explored.

Light management in hydrogenated amorphous silicon germanium solar cells

A finite difference time-domain (FDTD) simulation and experimental investigation of the enhanced light absorption in superstrate (PIN) type amorphous silicon germanium solar cells (a-SiGe:H) deposited on wet-etched Aluminum-doped zinc oxide (ZnO:Al) substrates are presented. Depending on the etching times, optimal vertical and lateral surface feature sizes, which balance the light scattering intensity and the light scattering angle, exist for a-SiGe:H solar cells. The surface morphology analysis, FDTD simulation, and experimental results concurrently show the maximum absorption of the long wavelength region will be achieved when the randomly textured surface with proper vertical and lateral surface feature sizes is applied in the solar cells. Due to the small inclination angle of 5°–20° on the wet-etched ZnO:Al surfaces, the light absorption is enhanced without producing a negative effect on the open circuit voltage (Voc) and fill factor (FF) of the a-SiGe:H solar cell, unlike the negative effects seen in hydrogenated microcrystalline silicon solar cell (μc-Si:H) on low-pressure chemical vapor deposition (LPCVD) ZnO substrates. An initial efficiency of 10.10% for PIN type a-SiGe:H single junction solar cell was achieved by adopting the optimized surface morphology.

Optical Improvement of ZnO-Coated Glass with New Refractive-Index Matching Layer Inserted at Glass/ZnO Interface

We prepared and applied a-SiOx thin films to hydrogenated microcrystalline silicon solar cells (µc-Si:H) as a front antireflection layer (FAL) in order to reduce optical reflection loss. By inserting the optimized SiOx FAL with a refractive index of ∼1.75 into the glass/ZnO interface a relative increase in short-circuit current density (Jsc) by 5% could be obtained which corresponded to an improved spectral response in the 550–950 nm wavelength regions. In addition, this optimized FAL did not deteriorate the properties of the ZnO layer because no significant changes in open-circuit voltage (Voc) and fill factor (FF) were observed. As a result, the cell with an efficiency of as high as 8.28% (Voc=0.495 V, Jsc=25.09 mA/cm2, FF=0.667) could be obtained.

Modelling of photo‐ and electroluminescence of hydrogenated microcrystalline silicon solar cells

AbstractPhotoluminescence (PL) and electroluminescence (EL) have received much attention as characterization techniques for photovoltaic devices. The methods are applied to study e.g. optical band‐gap, defect states, or quasi‐Fermi level splitting. Spatially resolved EL imaging is used to derive local junction voltage differences making it a fast inline characterization method for solar modules. However, the interpretation of EL and PL experiments on hydrogenated microcrystalline silicon (µc‐Si:H) solar cells is more complex hampering the direct determination of local voltage differences. In this work we integrated an existing model for PL of µc‐Si:H silicon with a commercial device simulator for thin‐film silicon devices. This way we extended the existing model from a spatially zero dimensional model to a one dimensional model which can also model EL. Furthermore the connection with an electrical device simulator enables the consistent modeling of EL, PL, and the electrical properties of the device. We compared experimental and simulation results for EL, PL and dark‐, and illuminated‐ current/voltage characteristics over a wide temperature range (80 – 300 K). The simulations and experiments are in good agreement in the temperature range from 170 K up to room temperature. In experiments we observed several effects which cannot be explained in the previous zero dimensional model (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Hydrogenated Microcrystalling Silicon Single-Junction NIP Solar Cells

The microstructure properties of hydrogenated microcrystalline silicon solar cells are investigated using Raman spectroscopy and x-ray diffraction. It was found that the increase of grain size and crystalline volume fraction with thickness is the main reason for the deterioration of cell performance as using constant hydrogen dilution technique. In order to adjust grain size and crystalline volume fraction along the growth direction, gradient hydrogen dilution technique has been adopted to control the structural evolution. The experiment results demonstrated that the performance of solar cell can be much improved when there's a higher crystallinity at n/i interface and a lower crystallinity at i/p interface. We have achieved an initial active-area efficiency of 5.7% (Voc=0.47V, Jsc=20.2mA/cm2, FF=60%) for the µc-Si:H single-junction n-i-p solar cells.

Efficient light management scheme for thin film silicon solar cells via transparent random nanostructures fabricated by nanoimprinting

We propose the use of transparent replicated random nanostructures fabricated via nanoimprinting on glass as next-generation superstrates for thin film silicon solar cells. We validate our approach by demonstrating short-circuit current densities for p-i-n hydrogenated microcrystalline silicon solar cells as high as for state-of-the-art nanotextured ZnO front electrodes. Our methodology opens exciting possibilities to integrate a large variety of nanostructures into p-i-n solar cells and allows to systematically investigate the influence of interface morphology on the optical and electronic properties of the device in order to further improve device performance.

Improvement of hydrogenated microcrystalline silicon solar cell performance by VHF power profiling technique

Hydrogenated microcrystalline silicon (μc-Si:H) solar cells were deposited with very high frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) process at high deposition rates in high-power and a high-pressure regime. A novel VHF power profiling technique, designed by dynamically decreasing the VHF power step by step during the deposition of μc-Si:H intrinsic layers, has been developed for the first time to control the structural evolution along the growth direction. The profiling parameters such as the amount and the rate of change in VHF power were optimized in detail and the experimental results demonstrate that this technique not only controls the microstructure evolution but also results in reduced ion bombardments on growth surface. Using this method, a significant improvement in the solar cell performance has been achieved. A high conversion efficiency of 9.36% ( V oc=542 mV, J sc=25.4 mA/cm 2, FF=68%) was obtained for a single-junction μc-Si:H p–i–n solar cell at a deposition rate of 12 Å/s. Then, the single-junction solar cell was used as a bottom component in micromorph solar cell, which leads to an efficiency of 11.14% ( V oc=1.367 V, J sc=11.92 mA/cm 2, FF=69.4%).

Nanoscale Characterization of Microcrystalline Silicon Solar Cells by Scanning Near-Field Optical Microscopy

The photovoltaic mapping technique of solar cells has been developed and tested on hydrogenated microcrystalline silicon (µc-Si:H) solar cells by scanning near-field optical microscopy (SNOM). Near-field light through a fiber probe illuminates the Si layer of a solar cell and then the photovoltaic effect appears locally. Topographic and photovoltaic images were obtained using a scanning probe and defective domains with diameters of 100–200 nm appeared in the photovoltaic images. A similar inhomogeneity was observed by conductive atomic force microscopy. The photovoltaic images demonstrate that film inhomogeneities affect solar cell performance. The results indicate that a scanning near-field microscope is useful for the quality monitoring of nanoscale junctions of hydrogenated microcrystalline silicon solar cells.

Optimization of n/i and i/p buffer layers in n–i–p hydrogenated microcrystalline silicon solar cells

Hydrogenated microcrystalline silicon (μc-Si:H) intrinsic films and solar cells with n–i–p configuration were prepared by plasma enhanced chemical vapor deposition (PECVD). The influence of n/i and i/p buffer layers on the μc-Si:H cell performance was studied in detail. The experimental results demonstrated that the efficiency is much improved when there is a higher crystallinity at n/i interface and an optimized a-Si:H buffer layer at i/p interface. By combining the above methods, the performance of μc-Si:H single-junction and a-Si:H/μc-Si:H tandem solar cells has been significantly improved.

Study of Nano-Scale Electrical Properties of Hydrogenated Microcrystalline Silicon Solar Cells by Conductive Atomic Force Microscope

The nano-scale current–voltage (I–V) characteristics of hydrogenated microcrystalline silicon (µc-Si:H) solar cells were studied by conductive atomic force microscope (conductive AFM) for the first time. A large local reverse (leakage) current was observed at a grain boundary, which was measured during the detection of the surface topography of a µc-Si:H solar cell in the contact mode. The grain boundary of the µc-Si:H solar cell might behave similarly to a current leakage path. In conductive AFM measurement, we found that surface topography of the µc-Si:H solar cell is composed of large convex regions. Here, a large convex region is formed by the aggregation of small grains with a diameter of ∼20 nm, which is similar to that of a silicon nanocrystallite determined by X-ray diffraction (XRD) measurement. We successfully evaluated the relationship between the nano-scale electrical properties and characteristics of grain boundaries. The obtained result indicates that the nano-scale quality of the µc-Si:H solar cell can be characterized by conductive AFM with a high experimental resolution of ∼1 nm.

Hydrogen dilution profiling for hydrogenated microcrystallinesilicon solar cells

The structural properties of hydrogenated microcrystalline silicon solar cells are investigated using Raman, x-ray diffraction, and atomic force microscopy. The experimental results showed a significant increase of microcrystalline volume fraction and grain size with increasing film thickness. The correlation between the cell performance and the microstructure suggests that the increase of grain size and microcrystalline volume fraction with thickness is the main reason for the deterioration of cell performance as the intrinsic layer thickness increases. By varying the hydrogen dilution in the gas mixture during deposition, microstructure evolution has been controlled and cell performance significantly improved.