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HL: Fachverband Halbleiterphysik

HL 27: Focus Session: Perspectives in Cu(In,Ga)Se 1

HL 27.2: Hauptvortrag

Donnerstag, 8. September 2022, 10:00–10:30, H33

Approaches to improve CIGS absorber quality and the CIGS/buffer interface to reach 24% efficiency and beyond — •Wolfram Witte — Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg (ZSW), Stuttgart, Germany

Cu(In,Ga)Se2 (CIGS) thin-film solar cells with polycrystalline absorber layers exhibit high power conversion efficiencies above 23% for small-area devices. The bandgap energy (Eg) of CIGS is tunable and the material can be used either as bottom cell within a tandem device, e. g. in combination with perovskite as a top cell or the CIGS cell can be applied as wide-bandgap top cell and combined with e. g. a silicon bottom cell. In spite of their excellent photovoltaic (PV) performance, it is apparent, when comparing the PV parameters of record single junction CIGS devices with the theoretical radiative limit, that various loss mechanisms are present in the devices. As few examples, the open-circuit voltage (Voc) and the fill factor (FF) are limited by non-radiative recombination and additional parasitic absorption takes place in the buffer and adjunct high-resistive (HR) layer, which can limit the short-circuit current (Jsc).

This contribution gives an overview on approaches to improve CIGS single-junction solar cells beyond 24%. Increasing grain size and/or eliminate the Ga/(Ga+In) grading in the absorber can reduce Voc losses and alloying of silver to CIGS can increase FF values.

To overcome parasitic absorption of the standard buffer system CdS/i-ZnO, the application of wide-bandgap buffer or HR materials such as Ga2O3 with Eg>4 eV can be an option to increase Jsc further.