Berlin 2015 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 5: Photovoltaics: CIGS and related compounds

HL 5.8: Talk

Monday, March 16, 2015, 11:15–11:30, EW 202

Photoreflectance and photoluminescence of Cu(In,Ga)S2 thin film solar cells — •Sergiu Levcenko, Joachim Klaer, Steffen Kretzschmar, and Thomas Unold — Helmholtz Zentrum Berlin für Materialien und Energie, Berlin, Germany

An increased open-circuit voltage and an improved photocurrent collection have been recently achieved in Cu(In1-x,Gax)S2 (CIGS)- thin film based cell due to properly designed gallium alloying in the absorber layer. Nevertheless, the open-circuit voltage deficiency in CIGS devices is still larger than in selenide chalcogenide-based solar cells. It is believed that recombination at CdS/CIGS interface strongly reduces the device performances.

In our study we employ the nondestructive and contactless photoreflectance (PR) and photoluminescence (PR) techniques for characterizing CIGS devices. The CIGS absorbers with Ga/Ga+In ratio of 0.27 were fabricated under copper-rich conditions by a rapid thermal process with subsequent removal of segregated CuS by KCN etching. The effect of sulfurization temperature and post deposition treatments (KCN etching, NaF, In2S3 and In thin layer extra depositions) of the absorber in CIGS devices was revealed by PR and PL measurements at a room temperature. In the near band edge region the PR spectra show distinct structures at 1.5 and 1.55eV, while the PL signal consist of a broad band at 1.5eV with full width at half maximum of 100meV. The structures in PL and PR spectra are found to be influenced by the absorber preparation parameters.