Kean Chern Fong

Near-infrared free carrier absorption in heavily doped silicon

Free carrier absorption in heavily doped silicon can have a significant impact on devices operating in the infrared. In the near infrared, the free carrier absorption process can compete with band to band absorption processes, thereby reducing the number of available photons to optoelectronic devices such as solar cells. In this work, we fabricate 18 heavily doped regions by phosphorus and boron diffusion into planar polished silicon wafers; the simple sample structure facilitates accurate and precise measurement of the free carrier absorptance. We measure and model reflectance and transmittance dispersion to arrive at a parameterisation for the free carrier absorption coefficient that applies in the wavelength range between 1000 and 1500 nm, and the range of dopant densities between ∼1018 and 3 × 1020 cm−3. Our measurements indicate that previously published parameterisations underestimate the free carrier absorptance in phosphorus diffusions. On the other hand, published parameterisations are generally ...

Perimeter Recombination Characterization by Luminescence Imaging

Perimeter recombination causes significant efficiency loss in solar cells. This paper presents a method to quantify perimeter recombination via luminescence imaging for silicon solar cells embedded within the wafer. The validity of the method is discussed and verified via 2-D semiconductor simulation. We demonstrate the method to be sufficiently sensitive in that it can quantify perimeter recombination even in a solar cell where no obvious deviation from ideality is observed in the current-voltage (J-V) curve.

Contact Resistivity of Evaporated Al Contacts for Silicon Solar Cells

The contact resistivity of evaporated Al on doped silicon is examined for a range of process conditions common to the fabrication of laboratory silicon solar cells. The effects of silicon surface preparation prior to evaporation, sintering temperature, the use of a shutter, and evaporation power are investigated. The presented evaporation conditions yielded the lowest published contact resistivity between Al- and phosphorus-doped Si over a large range of doping concentration. It is also demonstrated that a contact resistivity below 10-6 Ω·cm2 can be achieved without sintering. Three-dimensional simulations are utilized to compare the obtained results for evaporated Al contacts with those for passivated contacts.

Series resistance as a function of current and its application in solar cell analysis 37 th IEEE photovoltaic specialists conference

The series resistance of a solar cell varies with its operating conditions. However, most solar cell characterization is done by assuming the series resistance is represented as a constant value. This paper presents the application of the multi light method to extract R<inf>s-light</inf> and R<inf>s-dark</inf> as a function of current. Application of R<inf>s</inf>(J) to analysis of solar cell is demonstrated by extracting the R<inf>s</inf>-corrected J-V curve. This allows evaluation of the p-n junction without the parasitic R<inf>s</inf> effects. Since the R<inf>s</inf>(J) and R<inf>s</inf>-corrected J-V data is measured in high detail, the total losses from the R<inf>s</inf> and the pseudo efficiency can be measured without need of curve fitting. Finally, by including R<inf>s</inf>(J) to the modelling of solar cells, errors in parameterization caused by variation in R<inf>s</inf> value is eliminated.