Regensburg 2010 – scientific programme

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KR: Fachverband Kristallographie

KR 5: Topical Session Photovoltaic Materials I (with MM and BV MatWerk)

KR 5.2: Talk

Wednesday, March 24, 2010, 10:45–11:00, H4

Amorphous / crystalline silicon heterojunctions: Changes of structural and electronic properties upon low-temperature annealing — •Hannes Ner Beushausen, Tim Ferdinand Schulze, and Lars Korte — Silicon Photovoltaics, Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin, Germany

Solar cells based on amorphous/crystalline silicon (a-Si:H/c-Si) heterojunctions have gained much attention due to their high conversion efficiency. In order to increase the open circuit voltage V_oc of these solar cells, the prime objective is to ‘passivate’ the a-Si:H/c-Si interface, i.e. to suppress interface recombination of photogenerated charge carriers by saturating recombination-active dangling bonds.

Commonly, thin (3-10nm) undoped, nominally intrinsic (i)a-Si:H interlayers are used to acheive this passivation effect. The presented work discusses the structural and electronic changes induced by low temperature post-deposition annealing of such (i)a-Si:H/c-Si structures.

The microscopic configuration of hydrogen in the thin amorphous layers, as probed by Fourier transform infrared spectroscopy (FTIRS), is linked to the improvement of the passivation and a dramatic increase of effective minority carrier lifetime τ_eff. With 10 nm thick undoped a-Si:H layers values up to τ_eff > 4.5  ms, corresponding to interface recombination velocities S as low as 2 cm/s, were observed.