Marwan Dhamrin

Photoluminescence analysis of intragrain defects in multicrystalline silicon wafers for solar cells

Structures of intragrain defects were investigated by photoluminescence (PL) mapping tomography in multicrystalline silicon wafers for solar cells. PL dark patterns were observed in short minority carrier diffusion length regions, and we confirmed that the patterns came from the intragrain defects. The tomography revealed that the defects have planelike structures extended to the crystal growth direction. We also found that the growth conditions affect the structures of the defects: slower solidification leads to larger defects with lower density. Origins of the defects were analyzed by low-temperature PL spectroscopy, electron backscatter diffraction pattern measurement and etch-pit observation. We concluded that the defects are metal contaminated dislocation clusters which originate from small-angle grain boundaries.

Quality evaluation and improvement of iron-doped electromagnetic multycrystalline silicon wafers

The effect of iron doping in electromagnetic cast (EMC) Si wafers on minority carrier recombination lifetime has been extensively investigated by means of microwave detected photo-conductivity decay (μ-PCD) and surface photo-voltage (SPV) to discriminate impurities and defects for the lower crystal quality. Optical and thermal activations of doped iron are investigated to study the difference between the two techniques in obtaining iron concentration. Minority carrier lifetimes increase or decrease after activation due to the different optical injection levels of both the SPV and μ-PCD techniques. No noticeable effect of chemical passivation in obtained iron concentration is observed. Boron and phosphorus gettering and hydrogen passivation techniques are applied to improve minority carrier recombination lifetime. As a result, the crystal quality of the EMC Si wafers depends on defect centers rather than on iron impurities.

Growth of n-type multicrystalline silicon ingots from recycled CZ silicon feedstock

5 Ω·cm recycled n-type CZ silicon feedstock is used to grow n-type multicrystalline silicon to investigate the possibilities of using other feedstock resources available from the rejected silicon of the semiconductor industry. High diffusion lengths were realized near the bottom region due to the less impurity contamination and relatively high resistivity. The heavy accumulation of metal impurities and lower resistivity at the top of the ingot resulted in a poor diffusion length. The edges have lower diffusion lengths due to the different metallic contaminations diffused from the silicon nitride coating layer during the growth cycle. The response of the wafers to p-gettering was ascertained and carrier lifetimes improved further especially at the bottom of the ingot. The improvement was realized for a total of 80% of the ingot height with higher lifetimes exceeding values above 250 μs at Δn = 1015 cm−3 and 400 ·s at Δn = 1014 cm−3.

Light-Induced Lifetime Degradation of Multicrystalline Silicon Wafers and Solar Cells

Light-induced lifetime degradation of conventional cast, electromagne tic cast and heat exchanger method boron doped multicrystalline silicon wafers have bee n ext nsively studied. Results show that the carrier lifetimes of boron-doped conventional c ast , electromagnetic cast and heat exchanger method silicon wafers degrade as boron-doped Cz si licon wafers. However, boron-doped, electromagnetic cast and cast fabricated solar cells show a slight degradation of I sc, Voc and efficiencies comparing to wafer lifetime degradation. The degree of lifetime degradation depends on boron content and crystal quality suggesting the boron-oxygen compl ex models as a mechanism for lifetime degradation. Quality and stability of t he gallium-doped multicrystalline-Si wafers were intensively studied by means of quasi-steady-sta te photoconductance lifetime measurement. Results show that as-grown gallium-doped multicrystal line-Si wafers have high lifetimes and no significant degradation was observed under illuminat ion. The gallium-doped multicrystalline-Si wafers are a promising material for future photovolt aics.

Light-Induced Performance Degradation and Its Annihilation of Crystalline Silicon Solar Devices

Recent research on light-induced degradation of crystalline Si solar cells and modules is reviewed. The first paper on the issue was published in 1973 when efficiency of solar cells using 1 Ω·cm, B-doped CZ wafers degraded under illumination. Since mid 1990’s, several studies have been performed to investigate the mechanism of the light degradation and also to provide practical solutions to annihilate the degradation. Numerous experiments have been carried out regarding the effects of impurities including B, Ga, P, O and processing parameters such as annealing temperature. Recent analysis on weathered solar modules supported the LID is in agreement with a model attributing the lifetime degradation to oxygen and boron complex. The reduction of the concentration of B and O or substitution of boron by gallium are found to suppress the degradation and to realize cell efficiency further.Copyright