Shui-Yang Lien

Optimization of Recombination Layer in the Tunnel Junction of Amorphous Silicon Thin-Film Tandem Solar Cells

The amorphous silicon/amorphous silicon (a-Si/a-Si) tandem solar cells have attracted much attention in recent years, due to the high efficiency and low manufacturing cost compared to the single-junction a-Si solar cells. In this paper, the tandem cells are fabricated by high-frequency plasma-enhanced chemical vapor deposition (HF-PECVD) at 27.1 MHz. The effects of the recombination layer and the i-layer thickness matching on the cell performance have been investigated. The results show that the tandem cell with a p

Fabrication of Flexible Amorphous-Si Thin-Film Solar Cells on a Parylene Template Using a Direct Separation Process

In this paper, we report on the fabrication of flexible amorphous-silicon (a-Si) thin-film solar cells on a parylene template carried by a glass plate without any adhesive. The a-Si thin-film solar cells could be separated directly from the glass carrier after a process temperature of up to 200°C. The a-Si and parylene films were deposited using high-frequency plasma-enhanced chemical vapor deposition and a parylene reactor. The parylene-coated glass plate was treated with thermal annealing and Ar, N2, or O2 plasma. Moreover, SiNx and/or SiOx films were used as barrier layers between the transparent conductive oxide and parylene films. Details of different gas plasmas and barrier effects were investigated in terms of surface morphologies and solar cell characteristics. The a-Si thin-film solar cell on a parylene template with an open-circuit voltage of 0.74 V, a short-circuit current density of 15.69 mA/cm2, a fill factor of 54.98%, and a conversion efficiency of 5.78 % could be obtained. After the 10-mm-radius bending test for 5000 times, the a-Si thin-film solar cells still exhibited a conversion efficiency of 4.94%. These results indicated that a-Si thin-film solar cells on parylene templates have high potential for flexible photovoltaic applications.

Deposition and Characterization of High-Efficiency Silicon Thin-Film Solar Cells by HF-PECVD and OES Technology

The optical emission spectrometer (OES) is an effective experimental tool for monitoring plasma states and the composition of gases during the growth of silicon thin films by plasma-enhanced chemical vapor deposition. In this paper, hydrogenated amorphous silicon (a-Si) (a-Si:H) and microcrystalline silicon (μc-Si) thin films have been deposited in a parallel-plate radio frequency (RF) plasma reactor using silane and hydrogen gas mixtures. The plasma emission atmosphere was recorded using an OES system during the growth of the Si thin films. The plasma was simultaneously analyzed during the process using an OES method to study the correlation between growth rate and microstructure of the films. In the deposition, the emitted species (SiH*, Si*, and H*) were analyzed. The OES analysis supported a chemisorption-based deposition model of the growth mechanism. The effects of RF power, electron-to-substrate distance, and H2 dilution of the emission intensities of excited SiH, Si, and H on the growth rate and microstructures of the film were studied. Finally, single-junction a-Si:H and μc-Si solar cells were obtained with initial aperture area efficiencies of 9.71% and 6.36%, respectively. A tandem a-Si/μc-Si cell was also realized with an efficiency of 12.3%.

Large-Grain Polycrystalline Silicon Solar Cell on Epitaxial Thickening of AIC Seed Layer by Hot Wire CVD

Large-grain polycrystalline silicon (poly-Si) films were prepared on foreign substrates by the epitaxial thickening of seed layers. The seed layers were formed by aluminum-induced crystallization (AIC). Large-grain n-i-p poly-Si solar cells were deposited on epitaxial seeds by hot-wire chemical vapor deposition (HWCVD). Highly (93%) crystalline fractions with a lateral grain size of 5 ¿m and an intrinsic layer were grown without incubation. These techniques were employed to prepare large-grain poly-Si thin-film solar cells. An ITO/n-i-p (HWCVD)/p+ (AIC)/Ti/glass-structured poly-Si thin-film solar cell with an initial efficiency of 5.6% was obtained.

Power effect of ZnO:Al film as back reflector on the performance of thin-film solar cells

Aluminum-doped zinc oxide (AZO) is attracting interest as a potential transparent conducting oxide material for use in amorphous silicon (a-Si) thin-film solar cells. The absorption loss in the n-a-Si:H/Ag interface of the p-i-n thin film solar is high because the extinction coefficient of the Ag that is used as a back reflector is high. In this work, transparent conducting AZO films with a power in the range 500 W to 900 W prepared under Ar-ambient at a substrate temperature of 25 °C by RF-magnetron in-line sputtering. To minimize the absorption loss at longer wavelengths, an AZO layer we inserted at the n-a-Si:H/Ag interface of a solar cell with a glass/SnO2:F/p-a-SiC:H/buffer-layer/i-a-Si:H/n-a-Si:H/Ag structure and the performance of the cell with AZO/Ag deposited instead of Ag on the back contact, was investigated. The effects of the RF-magnetron sputtering deposition parameters on the optical, electrical and structural properties of the AZO films were analyzed. Optimized AZO films with high transmit...

Characterization of Nanocrystalline SiGe Thin Film Solar Cell with Double Graded-Dead Absorption Layer

The nanocrystalline silicon-germanium (nc-SiGe) thin films were deposited by high-frequency (27.12 MHz) plasma-enhanced chemical vapor deposition (HF-PECVD). The films were used in a silicon-based thin film solar cell with graded-dead absorption layer. The characterization of the nc-SiGe films are analyzed by scanning electron microscopy, UV-visible spectroscopy, and Fourier transform infrared absorption spectroscopy. The band gap of SiGe alloy can be adjusted between 0.8 and 1.7 eV by varying the gas ratio. For thin film solar cell application, using double graded-dead i-SiGe layers mainly leads to an increase in short-circuit current and therefore cell conversion efficiency. An initial conversion efficiency of 5.06% and the stabilized efficiency of 4.63% for an nc-SiGe solar cell were achieved.

Effectively Improved SiO2-TiO2 Composite Films Applied in Commercial Multicrystalline Silicon Solar Cells

Composite silicon dioxide-titanium dioxide (SiO2-TiO2) films are deposited on a large area of 15.6 × 15.6 cm2 textured multicrystalline silicon solar cells to increase the incident light trapped within the device. For further improvement of the antireflective coatings (ARCs) quality, dimethylformamide (DMF) solution is added to the original SiO2-TiO2 solutions. DMF solution solves the cracking problem, thus effectively decreasing reflectance as well as surface recombination. The ARCs prepared by sol-gel process and plasma-enhanced chemical vapor deposition (PECVD) on multicrystalline silicon substrate are compared. The average efficiency of the devices with improved sol-gel ARCs is 16.3%, only 0.5% lower than that of devices with PECVD ARCs (16.8%). However, from equipment depreciation point of view (the expiration date of equipment is generally considered as 5 years), the running cost (USD/watt) of sol-gel technique is 80% lower than that of PECVD method for the first five years and 66% lower than that of PECVD method from the start of the sixth year. This result proves that sol-gel-deposited ARCs process has potential applications in manufacturing low-cost, large-area solar cells.

Reliability Analysis of III-V Solar Cells Grown on Recycled GaAs Substrates and an Electroplated Nickel Substrate

This study involved analyzing the reliability of two types of III-V solar cells: (1) III-V solar cells grown on new and recycled gallium arsenide (GaAs) substrates and (2) the III-V solar cells transferred onto an electroplated nickel (Ni) substrate as III-V thin-film solar cells by using a cross-shaped pattern epitaxial lift-off (CPELO) process. The III-V solar cells were grown on new and recycled GaAs substrates to evaluate the reliability of the substrate. The recycled GaAs substrate was fabricated by using the CPELO process. The performance of the solar cells grown on the recycled GaAs substrate was affected by the uneven surface morphology of the recycled GaAs substrate, which caused the propagation of these dislocations into the subsequently grown active layer of the solar cell. The III-V solar cells were transferred onto an electroplated Ni substrate, which was also fabricated by using CPELO technology. The degradation of the III-V thin-film solar cell after conducting a thermal shock test could have been caused by microcracks or microvoids in the active layer or interface of the heterojunction, which resulted in the reduction of the external quantum efficiency response and the increase of recombination loss.

Graded Buffer Layer Effect on Performance of the Amorphous Silicon Thin Film Solar Cells

It is widely accepted that graded buffer layer between the p-layer and i-layer increase the efficiency of amorphous silicon solar cells. The open-circuit voltage (Voc), short current density (Jsc) and fill factor (FF) of the thin film solar cell are obviously increased. In the present study, hydrogenated amorphous silicon (a-Si:H) thin film solar cells have been fabricated by 27.12 MHz plasma enhanced chemical vapor deposition (PECVD). We discussed the three conditions at the p/i interface without buffer layer, buffer layer and graded buffer layer of thin film solar cells by TCAD software. The influences of the performance of the solar cell with the different buffer layer are investigated. The cell with graded buffer layer has higher efficiency compared with the cells without buffer layer and buffer layer. The graded buffer layer enhances the conversion efficiency of the solar cell by improving Voc and FF. It could be attributed to a reduction of interface recombination rate near the junction. The best performance of conversion efficiency (η)=8.57% (Voc=0.81 V, Jsc=15.46 mA/cm2, FF=68%) of the amorphous silicon thin film solar cell was achieved.

Fabrications of Si Thin-Film Solar Cells by Hot-Wire Chemical Vapor Deposition and Laser Doping Techniques

In this paper, we report a novel low-temperature process for fabricating a Si thin-film solar cell on a glass substrate. The cell structure was composed of glass/Al/p–i–n Si/Ag (grid), where the Si intrinsic layer was deposited by hot-wire chemical vapor deposition. All the doped Si layers were produced using a postgrowth laser-doping process. The hot-wire-deposited amorphous, microcrystalline and polycrystalline Si films showed significant differences in band gap and structural properties as determined by Raman spectroscopy, spectral optical transmission measurements, and transmission electron microscopy. The corresponding crystalline volume fractions were 93, 73, and 12%, respectively. It was found that the best solar cells were fabricated with a Si intrinsic layer deposited at the transition from microcrystalline to polycrystalline regimes. A preliminary efficiency of 1.9% was obtained for an n–i–p structured solar cell on an untextured glass substrate.