Lambert Johan Geerligs

Recombination activity of interstitial iron and other transition metal point defects in p- and n-type crystalline silicon

This work has been supported by the Australian Research Council and The Netherlands Agency for Energy and the Environment.

Iron detection in crystalline silicon by carrier lifetime measurements for arbitrary injection and doping

This work has been supported by NOVEM (The Netherlands Agency for Energy and the Environment) under contract no. 2020.01.13.11.2002.

Transition-metal profiles in a multicrystalline silicon ingot

The concentrations of transition-metal impurities in a photovoltaic-grade multicrystalline silicon ingot have been measured by neutron activation analysis. The results show that the concentrations of Fe, Co, and Cu are determined by segregation from the liquid-to-solid phase in the central regions of the ingot. This produces high concentrations near the top of the ingot, which subsequently diffuse back into the ingot during cooling. The extent of this back diffusion is shown to correlate to the diffusivity of the impurities. Near the bottom, the concentrations are higher again due to solid-state diffusion from the crucible after crystallization has occurred. Measurement of the interstitial Fe concentration along the ingot shows that the vast majority of the Fe is precipitated during ingot growth. Further analysis suggests that this precipitation occurs mostly through segregation to extrinsic defects at high temperature rather than through solubility-limit-driven precipitation during ingot cooling.

Light-induced boron-oxygen defect generation in compensated p-type Czochralski silicon

D.M. is supported by an Australian Research Council QEII Fellowship, L.J.G. acknowledges SenterNovem for support, and B.L. and J.S. acknowledge the support of the German Academic Exchange Service.

Distribution of iron in multicrystalline silicon ingots

The distribution of iron in multicrystalline silicon ingots for solar cells has been studied. A p- and a n-type multicrystalline ingot were intentionally contaminated by adding 53ppmwt (μg∕g) of iron to the silicon feedstock and compared to a reference p-type ingot produced from ultrapure silicon feedstock. The vertical total iron distribution was determined by neutron activation analysis and glow discharge mass spectrometry. For the intentionally Fe-contaminated ingots, the distribution can be described by Scheil’s equation with an effective distribution coefficient of 2×10−5. The interstitial iron concentration was measured in the p-type ingots. In the Fe-contaminated ingot, it is almost constant throughout the ingot and constitutes about 50% of the total concentration, which is in conflict with the previous studies. Gettering had a large impact on the interstitial iron levels by reducing the concentration by two orders of magnitude. Considerable trapping was observed at crystal defects on as-cut wafers...

Measuring dopant concentrations in compensated p-type crystalline silicon via iron-acceptor pairing

D.M. is supported by an Australian Research Council fellowship. L.J.G. would like to acknowledge SenterNovem for support.

High efficiency industrial screen printed n-type solar cells with front boron emitter

There is currently much interest in n-type base cells because of potential advantages, both of silicon base material and of cell process, for high efficiency. We present results of n-base solar cells on large area multicrystalline and monocrystalline silicon wafers, produced using simultaneous diffusion of phosphorus back surface field and boron emitter, screen-printed metallization and firing through. The cell process leads to record high efficiencies of 16.4% on mc-Si and 18.3% on monocrystalline wafers. We also consider material-related cell characteristics. It is experimentally demonstrated that in mc-Si a low resistivity is correlated to reduced cell efficiency, with the optimum base resistivity lying between 1.5 and 4 Ohm-cm. By characterising and modeling cells from monocrystalline Si, from nominally clean mc-Si, as well as from intentionally Fe-contaminated mc-Si, the impact of the mc-Si wafer purity on emitter properties is investigated in more detail.

Impact of Iron and Molybdenum in Mono and Multicrystalline Float-Zone Silicon Solar Cells

This paper investigates the impact of iron (Fe) and molybdenum (Mo) when they are introduced in the feedstock for mono- and multicrystalline Float-Zone (FZ) silicon (Si) growth. Neutron Activation Analysis shows that the segregation coefficient is in agreement with literature values. Lifetime maps on monocrystalline wafers show a uniform lifetime which decreases with the increase of contamination levels. Multicrystalline wafers show low lifetime areas, corresponding to grain boundaries and highly dislocated areas, which are independent from the contamination levels. Intra grain areas have a higher lifetime which changes with the contamination levels. The solar cells show a reduced diffusion length in multicrystalline uncontaminated cells compare to the monocrystalline uncontaminated. In multicrystalline cells the lowest level of Fe introduced (1012 atm/cm3) has hardly any influence, whereas in the Mo-contaminated cells the impact is visible from the lowest level (1011 atm/cm3). In monocrystalline cells the diffusion length is reduced already at the lowest contamination level of Fe.

Behaviour of Natural and Implanted Iron during Annealing of Multicrystalline Silicon Wafers

Changes in the concentration of interstitial iron in multicrystalline silicon wafers after high temperature annealing (900°C) have been monitored by carrier lifetime measurements. Two cooling rates were investigated. The first was considered ‘fast’, meaning the interstitial Fe had no time to diffuse to precipitation sites, and should therefore be frozen-in, despite being far above the solubility limit at lower temperatures. A second ‘slow’ cool down to 650°C allowed ample time for the Fe to reach the surfaces or other internal precipitation sites. Surprisingly, in both cases the Fe remained in a supersaturated state. This indicates the precipitation process is not diffusion-limited, and that another energetic barrier to precipitate formation must be present. Since the slow cooling used here is similar to the cooling rate experienced by multicrystalline ingots after crystallisation, this precipitate-impeding mechanism is probably responsible for the surprisingly high interstitial Fe concentrations often found in as-grown multicrystalline silicon wafers.