Excellent Average Diffusion Lengths of 600 μm of N-Type Multicrystalline Silicon Wafers After the Full Solar Cell Process Including Boron Diffusion (original) (raw)

N-type multicrystalline silicon wafers and rear junction solar cells

The European Physical Journal Applied Physics, 2005

N-type silicon presents several advantages compared to p-type material, among them, the most important is the small capture cross sections of metallic impurities, which are neatly smaller. As a consequence lifetime and also diffusion length of minority carriers should be neatly higher in n-type than in p-type, for a given impurity concentration. This is of a paramount interest for multicrystalline silicon wafers, in which the impurity-extended crystallographic defects interaction governs the recombination strength of minority carriers. It is experimentally verified that in 1.2 Ω cm raw wafers lifetimes about 200 µs and diffusion lengths around 220 µm are measured. These values increase strongly after gettering treatments like phosphorus diffusion or Al-Si alloying. Scan maps reveal that extended defects are poorly active, although in regions where the density of dislocations is higher than 10 6 cm −2. Abrupt p + n junctions are obtained by Al-Si alloying after annealing between 850 and 900 • C, which could be used for rear junction cells. Such cells can be processed by means of similar processing steps used to make conventional p-type base cells.

Fabrication of Monocrystalline Silicon Solar Cell using Phosphorous Diffusion Technique

This paper gives an overview of the materials and methods used for fabricating a monocrystalline silicon solar cell. The aim of this research is to study the solar cell fabrication technology and fabrication of monocrystalline silicon solar using phosphorous diffusion technique locally. For solar cell fabrication we have used several number of processing steps to get the final solar cell output. At first we took a p-type monocrystalline silicon wafer with square shape 150×150 mm2 in size, 200µm in thickness and which is a (100) oriented Czochralski Si wafer. Then Cleaning and texturing of the wafer was done using different chemical solutions and edge isolation of wafer was done using edge isolation paste. Phosphorous diffusion was done by diffusion furnace to form p-n junction using liquid Phosphorus Oxychloride (POCl3). Front and back side metallization was done by screen printers using silver paste and aluminum paste respectively. Then Rapid Thermal Annealing of the wafer was done at high zone temperature for curing the contact. Finally, fabricated solar cell was characterized by LIV tester.

THE PRODUCTION OF SOLAR CELLS FROM MONOCRYSTALLINE SILICON BY PHOSPHORUS DIFFUSION

This article outlines the materials and methods used to fabricate monocrystalline silicon solar cells. The purpose of this research is to study solar cell production technology and solar cell monocrystalline silicon production technology locally. We use several processing steps to obtain the final result of the solar cell. First, a square single crystal silicon wafer with a size of 150×150 mm 2 and a thickness of 200 μm is prepared. m, it is a oriented Cheklaussky (100) silicon wafer. The cleaning and texturing of the wafer are performed using various chemical solutions, and the edge of the wafer is isolated with an edge release paste. The phosphor is diffused in a diffusion furnace, a pn junction is formed with phosphorous oxychloride (POCl 3) liquid, and the front and back sides are respectively metalized by screen printing with silver and aluminum pastes. The plate is then subjected to rapid thermal annealing at the high temperature of the contact hardening zone. Finally, the LIV tester was used to characterize the solar cells produced. The data shows that the maximum power is 10.3369 W, and the maximum voltage power is 027504 V, full power current-37.5833 mA, open circuit voltage-0.555462 V, short-circuit current-56.5867 mA, fill factor-32.8868, battery efficiency-about 7%. Since Monocisralin solar cells are manufactured in India for the first time, the output of solar cells we produce is very low. The India Atomic Energy Commission (BAEC) has established a laboratory for the local production of solar cells. The processing technology, equipment temperature and the quality of air, water and other chemicals need to be optimized. To improve the efficiency of solar cells.

N-type multicrystalline silicon: material for solar cell processes with high efficiency potential

Conference Record of the Thirty-first IEEE Photovoltaic Specialists Conference, 2005.

We present the characterisation of directionally solidified n-type Si ingots. Three ingots with a range of bulk resistivities and different n-type doping elements (Sb, P and As) were studied. We show from Hall measurements that the mc-Si material has excellent electrical transport properties. The mobilities are close to the theoretical limit, which is given mainly by scattering at acoustical phonons. Mobilities so close to the theoretical value have, to our knowledge, not been demonstrated for comparable p-type mc-Si wafers. Additional measurements on high quality p-type mc-Si material support this statement. This m eans that other scattering mechanisms reduce the mobility in p-type mc-Si material, but are not present in n-type silicon. Lifetime measurements were conducted by µW-PCD using an iodine-ethanol surface passivation. This passivation was used preferably to SiNx, as in some experiments the hydrogen from the PECVD SiN seemed to passivate the bulk at deposition temperatures. Average values in excess of 120 µs over large areas were measured. In order to exploit the good material properties of ntype mc-Si, solar cell concepts must be developed and the processes optimised. B-diffusion is the most problematic step as it is considered to be both destructive to material quality and energy consuming. In this paper, we show that a BBr3-emitter diffusion is possible at moderate temperatures without degrading the carrier lifetime of the mc-Si material. An additional contribution from Libal et al. [1] on solar cell processing is included in this conference.

Diffusion-free high efficiency silicon solar cells

Progress in Photovoltaics: Research and Applications, 2012

Traditional POCl 3 diffusion is performed in large diffusion furnaces heated to~850 C and takes an hour long. This may be replaced by an implant and subsequent 90-s rapid thermal annealing step (in a firing furnace) for the fabrication of p-type passivated emitter rear contacted silicon solar cells. Implantation has long been deemed a technology too expensive for fabrication of silicon solar cells, but if coupled with innovative process flows as that which is mentioned in this paper, implantation has a fighting chance. An SiOx/SiN y rear side passivated p-type wafer is implanted at the front with phosphorus. The implantation creates an inactive amorphous layer and a region of silicon full of interstitials and vacancies. The front side is then passivated using a plasma-enhanced chemical vapor deposited SiN x H y . The wafer is placed in a firing furnace to achieve dopant activation. The hydrogen-rich silicon nitride releases hydrogen that is diffused into the Si, the defect rich amorphous front side is immediately passivated by the readily available hydrogen; all the while, the amorphous silicon recrystallizes and dopants become electrically active. It is shown in this paper that the combination of this particular process flow leads to an efficient Si solar cell. Cell results on 160-mm thick, 148.25-cm 2 Cz Si wafers with the use of the proposed traditional diffusion-free process flow are up to 18.8% with a V oc of 638 mV, J sc of 38.5 mA/cm 2 , and a fill factor of 76.6%.

Multicrystalline silicon wafers prepared from upgraded metallurgical feedstock

Solar Energy Materials and Solar Cells, 2008

A solution to the problem of the shortage of silicon feedstock used to grow multicrystalline ingots can be the production of a feedstock obtained by the direct purification of upgraded metallurgical silicon by means of a plasma torch. It is found that the dopant concentrations in the material manufactured following this metallurgical route are in the 10 17 cm À3 range. Minority carrier diffusion lengths L n are close to 35 mm in the raw wafers and increases up to 120 mm after the wafers go through the standard processing steps needed to make solar cells: phosphorus diffusion, aluminium-silicon alloying and hydrogenation by deposition of a hydrogen-rich silicon nitride layer followed by an annealing. L n values are limited by the presence of residual metallic impurities, mainly slow diffusers like aluminium, and also by the high doping level.

Local characterization of multicrystalline silicon wafers and solar cells

Recent Advances in Multidisciplinary Applied Physics, 2005

The current voltage characteristics of multicrystalline solar cells with individually designed front contact grids under different bias light conditions in the temperature range of 300 K to 340 K were investigated. Cells with a grid placed predominately on grain boundaries exhibit higher conversion efficiencies than cells where a great portion of the grid covers crystallites. The diode loss current observed for the first type of cells is governed by a thermal activation energy which is about 30 meV larger than found for other cells. This is attributed to a local increase of the recombination center density within grain boundaries.

Simulation of device parameters of high effi ciency multicrystalline silicon solar cells

The results of the simulation of the reported experimental results of high effi ciency multicrystalline silicon (mc-Si) solar cells, using PC1D software, are reported in this study. Results obtained by various groups have been incorporated and compared in this study. The highest effi ciency reported so far for mc-Si solar cells is 20·4% and 17–18% by research laboratories and commercial houses, respectively. The effi ciency can be further enhanced if passivation characteristics on both the front and back surface are improved. The role of back surface recombination has become more signifi cant in light of the use of thin mc-Si wafers by the solar cell industry. Based on the passivation characteristics and considering the understanding of the past three decades of studies, the authors have proposed and simulated a structure for mc-Si solar cells to improve the performance of the same. The results of our modeled structure of mc-Si solar cell show an effi ciency of 21·88% with short-circuit current density, Jsc = 39·39 mA/cm2, and open circuit voltage, Voc = 0·666 V.