Influence of wavelength on transient short-circuit current in polycrystalline silicon solar cells

The influence of the wavelength of monochromatic light on transient base photocurrent produced in a polycrystalline silicon solar cell n-p junction is theoretically analysed. A wavelength dependence in the initial part of the current decay is observed in cells with moderate grain boundaries effects. This influence is attenuated in polycrystalline cells with strong grain boundaries activity. A theoretical discussion about the wavelength dependence of the start of photocurrent decay on back surface recombination velocity is also reported.     

Electron-beam-induced current characterization of polycrystalline silicon solar cells

The use of the electron-beam-induced current mode of the scanning electron microscope for recombination studies in polycrystalline silicon solar cells is reviewed. The potential and some limits of the technique are discussed. Quantitative studies and representative results for edge-defined film-fed growth (EFG) ribbon solar cells and other kinds of silicon solar cells are presented and compared. Questions concerning recombination by impurities and defects such as dislocations, gain boundaries and SiC particles and the interactive effects of all these are discussed at some length.     

The impact of grain size on the photogenerated current in polycrystalline silicon solar cells

A simple one-dimensional model is proposed in order to investigate the impact of grain boundary recombination on the photogenerated current of polycrystalline silicon solar cells. The model is applied to calculate the degradation of the photocurrent caused by grain boundary recombination and the effective internal quantum efficiency as a function of grain size. It is found that the impact of grain boundary recombination on the photocurrent is significant in cells dominated by the long wavelength response, and in thicker cells.     

Laser-beam-induced current mapping evaluation of porous silicon-based passivation in polycrystalline silicon solar cells

In the present work, we report on the effect of introducing a superficial porous silicon (PS) layer on the performance of polycrystalline silicon (pc-Si) solar cells. Laser-beam-induced current (LBIC) mapping shows that the PS treatment on the emitter of pc-Si solar cells improves their quantum response and reduce the grain boundaries (GBs) activity. After the porous silicon treatment, mapping investigation shows an enhancement of the LBIC and the internal quantum efficiency (IQE), due to an improvement of the minority carrier diffusion length and the passivation of recombination centers at the GBs as compared to the reference substrate. It was quantitatively shown that porous silicon treatment can passivate both the grains and GBs.     

Excess minority carrier densities and transient short circuit currents in polycrystalline silicon solar cells

An attempt to solve the time dependent and three-dimensional diffusion equation for excess minority carrier density has been done. Analytical expressions giving the excess minority carrier densities in n and p regions of a polycrystalline silicon solar cell under illumination in short circuit conditions are proposed. The theoretical model based on a fibrously oriented square grain in polycrystalline sample is used. The grain boundary and grain size effects on excess minority carrier densities and photocurrents have been investigated.     

MIS and SIS solar cells on polycrystalline silicon

MIS- and SIS-structured solar cells are receiving much attention in the photovoltaic community. Apparently these cells could be a viable alternative to thermally diffused p-n junctions for use on thin film polycrystalline silicon substrates. In this paper we review MIS- and SIS-structured solar cells and the possible advantages of these structures for use with thin film polycrystalline silicon. The results of efficiency calculations are presented. We also consider the lifetime stability and fabrication techniques amenable to large-scale production. Finally the relative advantages and disadvantages of these cells and the results obtained are presented.     

Open-circuit voltage decay in polycrystalline silicon solar cells

Theoretical expressions for the open-circuit voltage decay induced by an electrical (dark current) or optical (photocurrent) excitation in a base-dominated polycrystalline silicon solar cell are derived. These two conventional transient methods which are of forward current induced open-circuit voltage decay (FCVD) and photoinduced open-circuit voltage decay (PVD) are investigated through the influence of grain size and grain boundary recombination velocity.     

PECVD grown silicon nitride AR coatings on polycrystalline silicon solar cells

Silicon nitride films produced by plasma enhanced chemical vapor deposition (PECVD) have been studied as antireflection (AR) coating on polycrystalline silicon solar cells. A substantial enhancement (28%) in the short circuit current (I_sc) has been obtained. The open circuit voltage (V_oc) of these cells has also been found to improve after silicon nitride deposition. The deposition conditions to optimise the improvement in the cell performance have been discussed.     

Thin film polycrystalline silicon solar cells on mullite ceramics

In this work, we present the structural quality of polycrystalline silicon films formed by high-temperature chemical vapor deposition (CVD) on mullite ceramics coated with spin-on flowable oxides (FO_x) serving as intermediate layers (ILs). The average grain size and the size distribution were investigated by optical microscopy. It is found that more than 65% of the surface of polysilicon films grown on boron-doped FO_x is covered by large grains of 5–10 μm. The intra-grain and inner-grain defects as well as the grain orientation were analyzed with the electron backscattering diffraction (EBSD) technique. Twin-type defects such as Σ3 and Σ9 are frequently present in these silicon layers, which are slightly (1 1 0) preferentially oriented. Finally, we present the photovoltaic data on test solar cells made on these CVD polysilicon films. An efficiency of about 3.3% is reported. The limiting factors, as well as possible improvements, are discussed.     

Hydrogen passivation of defects in polycrystalline silicon solar cells

The investigations of hydrogen passivation of defects in polycrystalline silicon produced by the Czochralski method have been carried on. The results presented give evidence that it is advisable to use this material to create cheap effective solar cells.     

Effects of low-temperature annealing on polycrystalline silicon for solar cells

The polycrystalline silicon material grown by the edge-defined film-fed growth technique, and often used in solar cell production, is known to be carbon and dislocation rich. Aim of this work was to explore the effect of low-temperature annealing in vacuum on properties of these structural defects, often present in different solar-grade materials. Electrical measurements by deep level transient spectroscopy revealed the presence of the defects typically found in dislocated silicon. Detailed analysis further suggested that they are also carbon related, exhibiting quite unexpected behavior at such low-temperature annealing. Moreover, photoluminescence results showed electron-hole droplet condensation at dislocations after such low-temperature annealing. This further supports the hypothesis that point defects are incorporated at dislocation cores rather than in a cloud at its proximity.     

玻璃衬底多晶硅薄膜太阳电池的制备

多晶硅薄膜太阳电池兼具单晶硅的高转换效率和多晶硅体电池的长寿命的特点,其制备工艺比非晶硅薄膜材料的制备工艺相对简化。文章介绍了多晶硅薄膜太阳电池材料制备工艺和材料性能;阐述了多晶硅薄膜太阳电池Si3N4膜的沉积和玻璃制绒等关键工艺;综述了玻璃衬底多晶硅薄膜太阳电池的发展现状。     

Variation of efficiency and short-circuit current of an array of silicon solar cells with intensity of solar radiation under tropical atmospheric conditions

We have studied the response of the efficiency and short-circuit current of an array of silicon solar cells to changes in intensity of solar radiation under tropical atmospheric conditions. The investigation was carried out simultaneously at two different geographical locations in Nigeria: Enugu (6.20°N, 7.30°E) and Port Harcourt (4.43°N, 7.10°E) (Port Harcourt is located very close to the sea, while Enugu is far away from the sea). Data collected from the two locations clearly reveal that the mean optimum efficiency is not constant, but decreases exponentially as the intensity of solar radiation increases. The short-circuit current, on the other hand, increases non-linearly with intensity of solar radiation and approaches some constant maximum value under very high insolation. The change in efficiency is above 70% as the intensity of solar radiation changes from 100 to 800 W m⁻². An empirical equation, relating the mean optimum efficiency to intensity of solar radiation, and an empirical equation, relating the mean short-circuit current to intensity of solar radiation, have been proposed. No previous similar work is available for comparison, but our results are consistent with the well-established fact that under cloudy conditions (and thereafter low insolation), short-wavelength radiation becomes predominant.     

High-voltage solar elements based on polycrystalline silicon

Problems connected with developing designs of high-voltage solar elements (SE) with vertical p- n transitions on the basis of polycrystalline silicon and also the results of analysis of new experimental data are considered. The photoelectric characteristics of SE with unilateral and bilateral illumination are presented. The prospects of using these SE in solar modules with parabolic-spherical and parabolic-cylindrical radiation concentrators are discussed.     

A study of electrical uniformity for monolithic polycrystalline silicon solar cells

The aim of this work is to investigate the electrical uniformity of monolithic polycrystalline silicon solar cells prepared by various process techniques. By a series of experiments such as P and Al impurity gettering and silicon nitride passivation, a new conclusion is that the application of P and Al gettering as well as silicon nitride passivation enhances the electrical uniformity of small area solar cells diced from the same polycrystalline silicon solar cells, even if impurity gettering is not effective when the dislocation density is above a threshold value of about 10⁶ cm⁻². The experiments give us some hints that when we cut large area polycrystalline silicon solar cells into small pieces needed for application, we should modify production process slightly.     

Equivalent model of monocrystalline, polycrystalline and amorphous silicon solar cells

The current–voltage (I–V) characteristics of monocrystalline, polycrystalline and amorphous silicon solar cells are measured in the dark. A two diodes equivalent model is used to describe the electronic properties of solar cells. The non-linear curve fitting of the dark I–V curves obtain besides the diode ideality factors and the reverse saturation currents, the series and shunt resistance of the solar cells. These parameters determine the fill factor and the efficiency of the solar cells.     

Development of low cost production technologies for polycrystalline silicon solar cells

To develop a technology of forming grooves for low cost cell production, a multi-blade wheel grinding method was investigated. The process time of groove formation on the surface of 10 × 10 cm² polycrystalline silicon substrate was reduced to 30 s by a newly developed high-speed groove formation machine. Simultaneous formation of junction and anti-reflection coating by atmospheric pressure chemical vapor deposition (APCVD) technique was also investigated. For electrodes formation process, single firing method for both side electrodes made possible to simplify the firing process and to speed up from a conventional speed of 400 mm/min to 5000 mm/min.     

Modelling of material properties influence on back junction thin polycrystalline silicon solar cells

The influence of polycrystalline silicon properties on the performances of thin back junction solar cells has been investigated by means of a 3-dimensional model taking into account grain size, grain boundary recombination, volumic recombination, and surface recombination. The drastic influence of front surface recombination has been confirmed. The grain size has been shown to be of minor importance provided the grain size is not too small and the grain boundaries are correctly passivated. An optimal base thickness has been determined which is all the smaller that the material is more imperfect.