High efficiency n-type Si solar cells on Al2O3-passivated boron emitters

Abstract

In order to utilize the full potential of solar cells fabricated on n-type silicon, it is necessary to achieve an excellent passivation on B-doped emitters. Experimental studies on test structures and theoretical considerations have shown that a negatively charged dielectric layer would be ideally suited for this purpose. Thus, in this work the negative-charge dielectric Al2O3 was applied as surface passivation layer on high-efficiency n-type silicon solar cells. With this front surface passivation layer, a confirmed conversion efficiency of 23.2% was achieved. For the open-circuit voltage Voc of 703.6mV, the upper limit for the emitter saturation current density J0e, including the metalized area, has been evaluated to be 29fA∕cm2. This clearly shows that an excellent passivation of highly doped p-type c-Si can be obtained at the device level by applying Al2O3.

Recombination processes in passivated boron-implanted black silicon emitters

“…43,44 Therefore, we focus first on this passivation layer and study the way it affects samples with various boron profiles. The emitter saturation current J 0e , which is a common measure for surface passivation and emitter recombination, is plotted in Fig.…”

“Zero-charge” SiO2/Al2O3 stacks for the simultaneous passivation of n+ and p+ doped silicon surfaces by atomic layer deposition

“…Even an ultrathin film of Al 2 O 3 of less than 2 nm was found to be sufficient to passivate the Si surface, when combined with a-SiN x :H (in short SiN x ) as anti-reflection coating (ARC) and/or capping layer [5,6]. The high levels of surface passivation provided by Al 2 O 3 allow for solar cells with high conversion efficiency, including p-type concepts (e.g, PERC or Al-LBSF cells [7,8]) as well as n-type concepts such as PERL cells [9]. Due to superior uniformity and passivation performance, ALD of Al 2 O 3 is currently piloted in industry [10].…”

Stability of Al2O3 and Al2O3/a-SiNx:H stacks for surface passivation of crystalline silicon

“…The impact of SiN deposition, postdeposition anneal, and firing on the surface passivation by Al 2 O 3 is shown for a representative selection of n-type c-Si samples in Table I 4 Subsequently, the samples were exposed to the high temperature firing step. The effective lifetime of sample B ͑Al 2 O 3 ͒ and samples D and E ͑Al 2 O 3 / SiN͒ decreased during firing, but remained in the millisecond range.…”

“…3 The application of a thin Al 2 O 3 film as a front passivation layer on a B-doped emitter has recently led to efficiencies as high as 23.2% for n-type c-Si solar cells. 4 For the implementation of Al 2 O 3 -based passivation schemes in high-volume manufacturing of c-Si solar cells, the compatibility of Al 2 O 3 with high temperature processing steps becomes a key issue. For example, a good thermal stability against high temperature "firing" processes of metal contacts is required for screen-printed solar cells.…”