Yuko Tawada

Thin film Si solar cell fabricated at low temperature

Abstract Research and development of our film Si solar cells are reviewed. Our developed film polycrystalline Si (poly-Si) cells are well described by the structure of natural surface texture and enhanced absorption with a back reflector (STAR), where the active poly-Si layer is fabricated by plasma chemical vapor deposition (CVD) at low temperature. The cell with a thickness of 2.0 μm demonstrated an intrinsic efficiency of 10.7% (aperture 10.1%). By combining poly-Si cell with an a-Si cell, a stabilized efficiency of 12% has been reached for a-Si:H/poly-Si/poly-Si cell structure.

High Efficiency Thin Film Silicon Hybrid Cell and Module with Newly Developed Innovative Interlayer

The paper discusses the development of a new light trapping scheme for a thin film Si based stacked cell and module, where a newly developed innovative interlayer is inserted between amorphous and microcrystalline Si thin film. This new interlayer leads intentional controlling of the refractive index of it. The interlayer with a lower refractive index of 1.7 at 600 nm exhibits both better reflection towards the top amorphous silicon cell and less absorption loss towards the bottom microcrystalline cell. We also proved by numerical simulation that the effect of the interlayer on light trapping towards the top cell is more enhanced with textured substrate. An initial cell efficiency of 15.0% has been achieved in a small area (1cm2) of its cell with this new interlayer. An initial aperture efficiency of 13.4% has been achieved for a 910times455 mm2 Si HYBRID PLUS module fabricated in a single chamber process of p-i-n microcrystalline cell, which was independently confirmed by AIST

High efficiency thin film silicon solar cell and module

An initial efficiency of 14.5% (Jsc=14.4mA/cm/sup 2/, Voc=1.41V, FF=71.9%) has been achieved for a-Si:H/transparent inter-layer/crystalline Si solar cell (total area of 1cm/sup 2/). Both a-Si and crystalline Si films were fabricated by plasma chemical vapor deposition at low temperature. The short circuit current (Jsc) was enhanced by the introduction of transparent interlayer without increasing the thickness of a-Si:H layer. An initial aperture efficiency of 12.3% has been achieved for 910/spl times/455mm/sup 2/ a-Si/crystalline Si thin film integrated solar cell module. Reasonably high deposition rate of 11 A/s for the deposition of crystalline Si for 1/spl times/1m/sup 2/ area has been achieved. By applying a deposition conditions of this high deposition rate, an initial aperture efficiency of 11.2% has been obtained above sized Si stacked solar cell module.

Effective conversion efficiency enhancement of amorphous silicon modules by operation temperature elevation

Abstract To eliminate photo degradation, we have proposed the elevation of the operating temperature of amorphous silicon modules by thermal insulators (polystylene foam) attached to them. A solar cell which degraded 19% with ordinary accelerated test condition (AM 1.5, 1 kW/m 2 , 48°C, 550 h) degraded only 13% at 90°C. The temperature coefficient of amorphous silicon solar cell is about 2 3 of that of crystalline silicon solar cells. A simple calculation predicts about 80% of the initial efficiency in actual operation. Modules whose initial efficiency is about 9.2% were field on 1 April 1996. These modules showed more than 8% effective efficiencies on 21 August 1996. The cell temperature elevation by thermal insulation depends not on the ambient temperature but on insolation and wind speed, and is about 8°C on average and 40°C at peak. Effective conversion enhancement by temperature elevation is about 1% of the conventional one, which can be larger in later observation.

Thin film poly-Si solar cell, with "star structure" on glass substrate fabricated at low temperature

The performances of thin film poly-Si solar cells with a thickness of less than 5 /spl mu/m on a glass substrate have been systematically investigated as a function of thickness. The cell of glass/back reflector/n-i-p poly-Si/ITO is well characterized by the structure of naturally surface texture and enhanced absorption with a back reflector (STAR), where the active i layer was fabricated by plasma chemical vapor deposition (CVD) at low temperature. The cell with a thickness of 3.5 /spl mu/m and 2.5 /spl mu/m demonstrated an intrinsic efficiency of 9.8%, as independently confirmed by Japan Quality Assurance. The optical confinement effect explains the excellent spectral response at long wavelength for our cells through the PC1D analysis. The higher sensitivity at long-wavelength of our cell which appeared in quantum efficiency curves is well correlated to the result of reflectance measurement. The open circuit voltage of 0.526 mV and the efficiency of 9.3% has been achieved for the cell with a thickness of 1.5 /spl mu/m, which was proved to be entirely stable with respect to the light-soaking. The stabilized efficiency of our developed a-Si:H/poly-Si/poly-Si stacked solar cell is 11.5%.

Wide band‐gap hydrogenated amorphous silicon carbide prepared from a liquid aromatic carbon source

By utilizing the aromatic molecule xylene, we have prepared hydrogenated amorphous silicon carbide (a‐SiC:H) for the first time from an aromatic carbon source. Good‐quality films are obtained, over a wide range of optical band gaps from 2.2 to 3.5 eV and carbon content from 0.4 to 0.9 atomic fraction. Infrared measurements indicate that the films contain an underlying inorganic network of bonded Si, C, and H atoms, as found in a‐SiC:H prepared from conventional carbon sources, but in addition, have substantial organic character, evidenced by a large amount of both aromatic and olefinic sp2 carbon bonding.

Thin film silicon solar cell and module

We have been developed a new light trapping scheme for thin film Si stacked module (Si HYBRID PLUS module), where a-Si:H/transparent inter-layer/microcrystalline Si thin film integrated large area solar cell module. An initial aperture efficiency of 13.1% has been achieved for 910/spl times/455 mm/sup 2/ Si HYBRID PLUS module, which was independently confirmed by AIST. This is the first time report for independently confirmed efficiency of large area thin film Si module with interlayer. The 19% increase of short circuit current (I/sub sc/) of this module was obtained by the introduction of transparent interlayer, namely internal light trapping. Stabilized efficiency of mini module exhibited the 12%. Outdoor performances of Si HYBRID (a-Si:H/micro-crystalline Si stacked) solar cell module have been investigated over 4 years for two different kind of modules (top and bottom cell limited, respectively). The Hybrid modules limited by the top cell have exhibited the more efficient performance rather than the bottom limited in natural sunlight at noon.

Low temperature Si crystal growth by alternating deposition and hydrogen etching sequences and its application to the p-layer of a-Si:H solar cells

Abstract Low temperature silicon crystal growth by alternating deposition and hydrogen etching sequences has been studied. The large area remote ECR H 2 plasma was used as an atomic hydrogen source. Epitaxial, polycrystalline, and microcrystalline Si thin films have been obtained below 400°C corresponding to various deposition conditions and kinds of substrates. Epitaxial films with electron mobilities exceeding 800 cm 2 /Vs were obtained on Si(100) substrates. By applying this method, very thin p-type microcrystalline Si films have been prepared on SnO 2 substrates below 200°C. The cross-sectional TEM micrographs showed that the longitudinal crystal size of microcrystalline on SnO 2 substrates was about 100–200 A. The a-Si:H solar cells with p-type microcrystalline Si had a higher open-circuit voltage than that of conventional cells by as much as 0.02–0.04 eV.

Improvement of the stability of amorphous silicon solar cells by light pulse treatment

Abstract The effect of cycles of exposure to high-intensity Xe light pulses and dark annealing on the properties of a-Si two-stacked tandem solar cells was investigated. The light pulse induced decrease in efficiency becomes smaller with consecutive exposure/anneal cycles, mainly as a result of stabilisation of the fill factor. The optimum treatment temperature was found to be 160°C, giving a cell with an initial efficiency of 10.1% which showed 35% smaller degradation than untreated cells after 21 h under AM1.

Light-induced effects in a-Si/a-Si two-stacked tandem junction solar cells

Abstract A-Si/a-Si two-stacked tandem junction solar cell submodules were optimized on the textured SnO2 substrate. The highest module efficiency of 9.3% was obtained. The light-induced degradation of a-Si two-stacked tandem junction solar cells was simulated by using two types of degradation models (bond-breaking model and hole trapping model). In each case, the initial degradation of the tandem type cell can be well simulated. By optimizing the device parameters by using the computer simulation and adopting these results for the cell fabrication, the stable tandem type submodule of less than 3% degradation after 100h sunlight irradiation will be obtained.