Thomas Lauinger

Record low surface recombination velocities on 1 Ω cm p‐silicon using remote plasma silicon nitride passivation

Outstanding surface passivation of low‐resistivity single‐crystalline p‐silicon is reported using silicon nitride fabricated at low temperature (375 °C) in a remote plasma‐enhanced chemical vapor deposition system. The effective surface recombination velocity Seff is determined as a function of the bulk injection level from light‐biased photoconductance decay measurements. On polished as well as chemically textured silicon wafers we find that our remote plasma silicon nitride provides better surface passivation than the best high‐temperature thermal oxides ever reported. For polished 1.5 and 0.7 Ω cm p‐silicon wafers, record low Seff values of 4 and 20 cm/s, respectively, are presented.

Optimization and characterization of remote plasma-enhanced chemical vapor deposition silicon nitride for the passivation of p-type crystalline silicon surfaces

In a recent letter [Lauinger et al., Appl. Phys. Lett. 68, 1232 (1996)] we have shown that record low effective surface recombination velocities Seff of 4 cm/s have been obtained at ISFH on low-resistivity (1 Ω cm) p-type crystalline silicon using microwave-excited remote plasma-enhanced chemical vapor deposition (RPECVD) of silicon nitride at low temperature (300–400 °C). As an important application, this technique allows a simple fabrication of rear-passivated high-efficiency silicon solar cells with monofacial or bifacial sensitivity. In this work, we present details of the required optimization of the PECVD parameters and a characterization of the resulting silicon nitride films. All deposition parameters are shown to strongly affect Seff as well as the stability of the films against the ultraviolet (UV) photons of terrestrial sunlight. A clear correlation between Seff and the film stoichiometry is observed, allowing a simple control and even a rough optimization of the surface passivation quality by ...

Injection‐level dependent surface recombination velocities at the silicon‐plasma silicon nitride interface

Experimental evidence is presented that the effective surface recombination velocity (Seff) at p‐silicon surfaces passivated by silicon nitride films (fabricated in a plasma‐enhanced chemical vapor deposition system) shows an injection‐level dependence similar to the behavior of thermally oxidized silicon surfaces. Using the microwave‐detected photoconductance decay method, injection‐level dependent Seff measurements were taken on nitride‐passivated p‐silicon wafers of different resistivities (1.5–3000 Ω cm). The obtained Seff values also show that for low‐resistivity substrates (≤2 Ω cm), nitride passivation is as effective as conventional oxide passivation (and even superior at low injection levels) and furthermore offers the advantage of a less pronounced injection‐level dependence.Experimental evidence is presented that the effective surface recombination velocity (Seff) at p‐silicon surfaces passivated by silicon nitride films (fabricated in a plasma‐enhanced chemical vapor deposition system) shows an injection‐level dependence similar to the behavior of thermally oxidized silicon surfaces. Using the microwave‐detected photoconductance decay method, injection‐level dependent Seff measurements were taken on nitride‐passivated p‐silicon wafers of different resistivities (1.5–3000 Ω cm). The obtained Seff values also show that for low‐resistivity substrates (≤2 Ω cm), nitride passivation is as effective as conventional oxide passivation (and even superior at low injection levels) and furthermore offers the advantage of a less pronounced injection‐level dependence.

Record low surface recombination velocities on low-resistivity silicon solar cell substrates

In this paper, the lowest ever reported effective surface recombination velocities S/sub eff/ on typical p-type low-resistivity silicon solar cell substrates are presented. We obtain this surface passivation by means of remote plasma silicon nitride films fabricated at 375/spl deg/C. On polished as well as on chemically textured silicon surfaces, the applied low-temperature passivation scheme is significantly superior to high-temperature passivation by state-of-the-art thermal oxides. On polished 1.5-/spl Omega/cm p-Si wafers, an extremely low S/sub eff/ value of 4 cm/s is obtained. Because of the enormous potential of these plasma silicon nitride films as passivation medium for the rear surface of silicon solar cells, we also investigate silicon nitride-passivated, Al grid-covered p-Si surfaces as used by us in bifacial solar cells. On such samples we measure spatially averaged S/sub eff/ values as low as 135 cm/s.

UV stability of highest-quality plasma silicon nitride passivation of silicon solar cells

The UV stability of Si solar cells passivated by low-temperature remote PECVD silicon nitride films is tested. Perfect stability of the front surface passivation and the rear surface passivation of both p-n junction as well as MIS-IL Si solar cells is observed. Using the microwave-detected photoconductance decay (MW-PCD) method, a very small and slow degradation of the differential effective surface recombination velocity S/sub eff.d/ is observed at silicon nitride-passivated p-Si surfaces corresponding to the nonmetallized rear surface regions of bifacial cells. However, the degradation is too small to have any impact on the long-term stability of encapsulated 17-18% rear efficient bifacial cells. Thin-silicon-oxide/silicon-nitride double layers incorporating Cs as used at the front surface of MIS-IL solar cells provide perfectly stable and excellently low differential S/sub eff.d/ values of 23 cm/s on 1.5-/spl Omega/cm wafers. Applied to the rear surface of bifacial Si solar cells, this double-layer scheme gives the potential of stable rear efficiencies of even 20%.

SUNALYZER-a powerful and cost-effective solar cell I-V tester for the photovoltaic community

SUNALYZER, a powerful yet cost-effective solar cell I-V tester is introduced. The costs of the optical components are kept at tolerable levels by means of a halogen lamp array. In combination with a computerized height adjuster, this lamp system allows the measurement of a set of illuminated I-V curves covering the intensity range from 0.1 to 4 Suns. Furthermore, the dark I-V curve is measured over a current range of up to 8 orders of magnitude. From these measurements, an analysis subroutine accurately determines the solar cells series resistance R/sub s.light/ and R/sub s.dark/ as well as the diode ideality factor n and the saturation current density J/sub 0/ as a function of the external current density. Furthermore, design modifications are described which allow for speedy, fully automated illuminated I-V measurements, as required for testing and sorting purposes in solar cell production lines.