Dresden 2014 – scientific programme

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DS: Fachverband Dünne Schichten

DS 37: Focus Session: Sustainable Photovoltaics with Earth Abundant Materials I

DS 37.2: Invited Talk

Thursday, April 3, 2014, 10:00–10:30, CHE 91

Energy band alignment at interfaces of polycrystalline semiconductors for thin film solar cells — •Andreas Klein — Technische Universität Darmstadt, Germany

Thin film solar cells utilizing CdTe or Cu(In,Ga)Se₂ chalcogenide semiconductors have reached conversion efficiencies close to or even above 20%, respectively. The device structure of these cells is characterized by a sequence of an ohmic back contact, an unintentionally doped medium-gap chalcogenide as light absorber, a wide-gap chalcogenide buffer layer, and a transparent conducting oxide (TCO) front contact. Critical for high conversion efficiencies of such heterojunction devices is the energy band alignment at the various interfaces, which enable or block current transport. Historically, suitable interface properties have been achieved mainly by empirical device optimization. Photoelectron spectroscopy (PES) can provide detailed information on the chemical and electronic interface properties. This contribution introduces the experimental approach of interface analysis using PES and reviews available experimental data and understanding of interfaces for various thin film solar cells. In addition to interface properties of CdTe, Cu(In,Ga)Se₂, metallic back contacts, and TCO front contacts, the challenge of finding new absorber materials and device structures will be particularly addressed.