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HL: Fachverband Halbleiterphysik

HL 1: Perovskite and Photovoltaics I (joint session HL/KFM)

HL 1.5: Vortrag

Montag, 17. März 2025, 10:30–10:45, H13

Microscopic origins of band-gap broadening and its relationship with Urbach tails in photovoltaic absorbers — •Daniel Abou-Ras — Helmholtz-Zentrum Berlin, Germany

The broadening of absorption edges is a general feature found in numerous semiconductors used as absorber layers for thin-film solar cells. Since this broadening gives rise to radiative losses of the open-circuit voltage, it is of importance to control the broadening by corresponding material design of the photovoltaic absorber materials. The present work provides an overview of the microscopic origins of band-gap broadening, addressing not only compositional aspects and microstrain, but also electrical and optoelectronic properties on the sub-µm scale. In addition, the Urbach energy extracted from absorptance or quantum efficiency spectra has been used broadly to quantify disorder in a material. However, up to date, it has not only not been clarified what the microscopic origins of Urbach tails are; the present contribution also shows that there is no direct correlation between the broadening of the absorption edge and the Urbach energy of a semiconductor, as verified for about 30 different photovoltaic absorbers.

Keywords: photovoltaic solar cells; band-gap broadening; radiative losses; Urbach tails