Recently, an important trend within crystalline silicon solar cell processing is the assignment of a more prominent role to thin (≤ 150 μm) substrates. This considerably reduces dominant material costs, albeit at the expense of giving up well-established solar cell processing steps, such as the screenprinted aluminium back-surface-field (BSF) and contact formation, due to excessive warping of the cells. Next to this, thinner wafers evidently increase the need for excellent rear-surface passivation-schemes. Finally, it is generally accepted that when using multicrystalline Si (mc-Si) substrates, dedicated processing-steps are essential to upgrade the average minority charge carrier lifetime in the bulk, τbulk. Generally, this is done by applying gettering and/or hydrogenation-steps, both being relatively high temperature steps. Futhermore, for such thin solar cells, to be sufficiently efficient, the minority charge carrier diffusion length in the bulk, Lbulk, should exceed twice the waferthickness. This paper describes a solar cell processing route potentially overcoming all three constraints as pointed out on thinp-type mc-Si silicon substrates. It will be shown that the use of POCl3-diffusion is rather essential to increase τbulk. For the rear side, it is then shown that direct Plasma Enhanced Chemical Vapour Deposited (PECVD) a-Si:H layers can yield surface recombination velocities with values below 1.5 m.s-1. This is achieved throughout a broad excess minority charge carrier density, Δn. range of about 5 × 1018 to 5 × 1022m-3, for 20nm thick intrinsic PECVD a-Si layers on top of 1.0 times; 10-2Ω.m p-type Float Zone (FZ) silicon wafers. Finally, results are given of subsequent POCl3 gettering and PECVD a-Si:H surface passivation throughout a complete cast mc-Si Polix 1.0 × 10-2Ω.m p-type ingot by means of Leff extraction.
|Original language||English (US)|
|Number of pages||8|
|Journal||Acta Physica Slovaca|
|State||Published - Apr 1 2003|
ASJC Scopus subject areas
- Physics and Astronomy(all)