From lifetime measurements, including a direct experimental comparison with thermal SiO2, a-Si:H, and as-deposited a-SiNx:H, it is demonstrated that Al2O3 provides an excellent level of surface passivation on highly B-doped c-Si with doping concentrations around 1019cm−3. The Al2O3 films, synthesized by plasma-assisted atomic layer deposition and with a high fixed negative charge density, limit the emitter saturation current density of B-diffused p+-emitters to ∼10 and ∼30fA∕cm2 on >100 and 54Ω∕sq sheet resistance p+-emitters, respectively. These results demonstrate that highly doped p-type Si surfaces can be passivated as effectively as highly doped n-type surfaces.
We make up the free energy balance for thermalized electrons and holes in a solar cell. Equations for the loss rates of free energy due to recombination and transport of carriers are derived. The well known expression for Joule heat dissipation also holds for the free energy loss by diffusive transport. All loss rates have units of mW/cm2. Thus transport losses become directly comparable in magnitude to recombination losses. The latter are usually quantified in mA/cm2 rather than mW/cm2. The impact of various loss mechanisms on the power output of the cell, also in mW/cm2, becomes directly apparent.
The aim of this paper is to clarify which mean value can be used to predict multicrystalline Si (mc-Si) solar cell performance from lifetime distributions on wafers prior to production. Therefore, a numerical device simulation model is presented that predicts cell performance very precisely from lifetime distributions. This model is used to derive a simple lifetime averaging procedure, which can be used as a criterion for excluding low-quality wafers from production. Compared with standard mean values such as the arithmetic, harmonic, or geometric mean, the criterion derived here significantly reduces the number of mistakenly rejected wafers prior to cell production. In an exemplary case study where 1000 different lifetime distributions were analyzed, our new procedure misjudged only 13 wafers, in contrast with 158 wafers when using the arithmetic mean, 109 wafers when using the geometric mean, and 78 when using the harmonic mean. Further, the influence of lower lifetime regions on mc-cell performance is quantified, showing that low lifetime regions cannot be overcompensated with higher lifetimes in general.
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