Variation of the layer thickness to study the electrical property of PECVD Al2O3 / c-Si interface

AbstractThis paper focusses in particular on the influence of the layer thickness on the passivation quality, the charge density and the interface defects of PECVD Al2O3 passivation layers on c-Si surfaces. The surface recombination velocity and the interface defect density are observed to increase by decreasing the layer thickness. However, the density of negative charges remains almost constant with values around 3 1012cm-2. An optimal passivation quality is obtained for thicknesses of 15nm and higher. A linear relation between surface recombination velocity and Dit was established, allowing the estimation of the electron capture cross section (σn ∼ 10-13cm-2).Additionally, we measured the capture cross section of holes and electrons using DLTS measurement. The results are found to be very similar to reported values for silicon dioxide. This supports the idea that the chemical passivation of crystalline silicon by Al2O3 is performed by the interstitial SiO2 layer

Numerical modeling of highly doped Si:P emitters based on Fermi–Dirac statistics and self-consistent material parameters

We have established a simulation model for phosphorus-doped silicon emitters using Fermi–Dirac statistics. Our model is based on a set of independently measured material parameters and on quantum mechanical calculations. In contrast to commonly applied models, which use Boltzmann statistics and apparent band-gap narrowing data, we use Fermi–Dirac statistics and theoretically derived band shifts, and therefore we account for the degeneracy effects on a physically sounder basis. This leads to unprecedented consistency and precision even at very high dopant densities. We also derive the hole surface recombination velocity parameter Spo by applying our model to a broad range of measurements of the emitter saturation current density. Despite small differences in oxide quality among various laboratories, Spo generally increases for all of them in a very similar manner at high surfacedoping densities Nsurf. Pyramidal texturing generally increases Spo by a factor of five. The frequently used forming gas anneal lowers Spo mainly in low-doped emitters, while an aluminumanneal(Al deposit followed by a heat cycle) lowers Spo at all Nsurf.P.P.A. is on a Postdoctoral Fellowship from the Australian Research Council ~ARC!. The Center for Photovoltaic Engineering is supported by ARC’s Special Research Centres Scheme. A.C. and M.K. also acknowledge funding by the ARC

Silicon solar cell–integrated stress and temperature sensors for photovoltaic modules

We propose silicon solar cell–integrated stress and temperature sensors as a new approach for the stress and temperature measurement in photovoltaic (PV) modules. The solar cell–integrated sensors enable a direct and continuous in situ measurement of mechanical stress and temperature of solar cells within PV modules. In this work, we present a proof of concept for stress and temperature sensors on a silicon solar cell wafer. Both sensors were tested in a conventional PV module setup. For the stress sensor, a sensitivity of (−47.41 ± 0.14)%/GPa has been reached, and for the temperature sensor, a sensitivity of (3.557 ± 0.008) × 10$^{-3}$ K$^{-1}$ has been reached. These sensors can already be used in research for increased measurement accuracy of the temperature and the mechanical stress in PV modules because of the implementation at the precise location of the solar cells within a laminate stack, for process evaluation, in‐situ measurements in reliability tests, and the correlation with real exposure to climates

Impact of light-induced recombination centres on the current-voltage characteristic of Czochralski silicon solar cells

We have investigated the effect of the light-induced deep-level recombination centre specific to boron-doped, oxygen-contaminated Czochralski (Cz) silicon on the current-voltage characteristic of Cz silicon solar cells by means of numerical simulation and experiment. The device simulation predicts the occurrence of a shoulder in the current-voltage curve after activating the characteristic recombination centre. The physical reason for the non-ideal diode behaviour, characterised by a local ideality factor greater unity, is the strongly injection-level-dependent bulk lifetime produced by the deep-level centre. The increased ideality factor causes a degradation in fill factor with the magnitude of degradation depending on the doping concentration of the Cz silicon base. In order to verify the theoretical predictions experimentally, we have performed measurements on high-efficiency Cz silicon solar cells. Current-voltage curves recorded before and after light degradation clearly show the theoretically predicted change in shape and the reduction in fill factor. An excellent quantitative agreement between calculation and experiment is obtained for the subtracted current-voltage curves measured after and before illumination

Improved Silicon Surface Passivation by ALD Al2O3/SiO2 Multilayers with In‐Situ Plasma Treatments

Abstract Al2O3 is one of the most effective dielectric surface passivation layers for silicon solar cells, but recent studies indicate that there is still room for improvement. Instead of a single layer, multilayers of only a few nanometers thickness offer the possibility to tailor material properties on a nanometer scale. In this study, the effect of various plasma treatments performed at different stages during the ALD deposition of Al2O3/SiO2 multilayers on the silicon surface passivation quality is evaluated. Significant improvements in surface passivation quality for some plasma treatments are observed, particularly for single Al2O3/SiO2 bilayers treated with a H2 plasma after SiO2 deposition. This treatment resulted in a surface recombination parameter J0 as low as 0.35 fA cm−2 on (100) surfaces of 10 Ω cm n‐type silicon, more than a factor of 5 lower than that of Al2O3 single layers without plasma treatment. Capacitance‐voltage measurements indicate that the improved surface passivation of the plasma‐treated samples results from an enhanced chemical interface passivation rather than an improved field effect. In addition, a superior temperature stability of the surface passivation quality is found for various plasma‐treated multilayers

Improved quantitative description of Auger recombination in crystalline silicon

An accurate quantitative description of the Auger recombination rate in silicon as a function of the dopant density and the carrier injection level is important to understand the physics of this fundamental mechanism and to predict the physical limits t