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ECN publicatie:
Mercury: a novel design for a back junction back contact cell with front floating emitter for high efficiency and simplified processing
Gepubliceerd door: Publicatie datum:
ECN Zonne-energie 22-9-2014
ECN publicatienummer: Publicatie type:
ECN-M--14-050 Conferentiebijdrage
Aantal pagina's: Volledige tekst:
8 Download PDF  (1182kB)

The back junction back contact cell, and more specifically the interdigitated back contact (IBC) cell is among the most appropriate cell design to achieve high cell efficiency. An important aspect to improve manufacturability (e.g. reduce cost) of the cell and module is to increase the rear side back surface field (BSF) region width, as this currently constitutes the smallest feature size in the diffusion pattern of an IBC cell. We propose a novel design of an IBC cell that enhances the effective lateral transport of minority carriers (holes) and therefore allowing wide BSF regions. The novel design features an appropriate conductive and well passivated p++-doped layer, referred to as a front floating emitter (FFE), on the front surface of the IBC cell. This conductive FFE enables equally-sized interdigitated doping patterns of positive and negative polarities on the rear, with similar cell pitch and efficiency compared to traditional IBC cells. It also enables larger interconnection pads for easier module interconnection with marginal performance loss. Additional advantages are expected such as relaxed alignment tolerances for patterning as well as interconnection processes. We report on the proof-of-principle of this new cell concept, which we name “Mercury”, brought forward by 2D simulations and experimental results on small and 6 inch cells. So far, based on an industrial process flow with stable results, these cells yield full area efficiencies up to 19.6% on 6 inch and short-circuit densities well above 41 mA/cm2 for masked smaller cells. Additionally, the Mercury cells show less efficiency loss at low illumination intensity than a standard p-type H-pattern cell. Furthermore, we present the interconnection and cell design of our 6 inch Mercury cell and prove that our first 4-cell Mercury modules pass the thermal cycling and damp heat test of the IEC protocol.

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