Research Projects
The department contributes to the research subjects Compound Semiconductors (Multijunction solar cells based on III-V semiconductors) and New Materials and Solar Cell Structures within the Helmholtz Research Programme Renewable Energies/Thin-film Photovoltaics. The two projects involve the preparation and analytics of (i) III-V multi-junction solar cell structures and (ii) nano-structured organic-inorganic hybrid devices. Highly sophisticated analytical tools are employed: Optical in-situ spectroscopy in the MOCVD reactor, surface science tools in ultra-high-vacuum made accessible via contamination-free MOCVD to UHV transfer, direct time-resolved spectroscopy in all the relevant time windows from femtoseconds to seconds. Data obtained with these powerful analytical tools are supplied to partners in joint projects, i.e. research institutes, industry, and university groups. Photo-induced electron-hole dynamics of inorganic/organic hybrid devices and epitaxial III-V semiconductors are investigated with real time femtosecond spectroscopy and photo-electrical measurements. III-V compounds: Theoretical calculations show, that a band gap Egap in the range of 1eV is highly desirable for III-V solar cells with multiple junctions. III–V semiconductors with band gaps in the range of 1 eV can be grown epitaxially on the lattice constant of InP. Aiming at the improvement of the conversion efficiency of a high-efficiency multi-junction solar cell based on the lattice constant of InP solar cells using new materials and alternative, non-gaseous, i. e. much less toxic, precursors are employed. Different types of tandem solar cells based on the lattice constant of InP are explored to achieve conversion efficiencies exceeding 40%.
Organic-inorganic hybrid systems: Electron injection and recombination at the interface of molecular absorber layers and nano-structured or bulk semiconductors is studied with the aim of setting fundamental foundations for a prototype all solid-state composite inorganic/organic solar cell for the low cost regime. Charge carrier dynamics of III-V semiconductor building blocks for highly efficient ‘next generation’ photovoltaic and photonic devices are examined with sophisticated surface sensitive laser spectroscopy with the best time resolution presently available.
