Our research focus is on thin film oxides that combine optical transparency with electrical functionality, including transparent conducting oxides (TCOs) and electrochromic oxides for applications in solar cells and switchable windows. Scalable vacuum and non-vacuum deposition approaches are developed together with innovative photonic post-deposition treatments for enhanced optoelectronic performance.
Solution growth, printing of nanoparticle inks, spray pyrolysis offer vacuum-free deposition of oxides for cost-effective manufacturing yet their performance needs to be improved as compared to reference vacuum processes. One research highlight is an aqueous solution growth of transparent and conductive ZnO layers with electrical resistivity down to 3x10-3 Ohm cm and optical transparency of > 90%, which is applicable to any temperature-sensitive and non-conductive substrates.
Sputtering is a large-area, industry-relevant method for depositing TCOs and electrochromic materials. Our focus is on new material compositions for higher corrosion stability, tunable workfunction, high mobility as well as low-sputter-damage deposition. One example is amorphous hydrogenated In2O3 layers used as transparent contacts in CIGS solar cells leading to an improved open circuit voltage as compared to reference Al:ZnO-based devices.
Photonic curing and annealing
Photon-assisted post-treatments such as rapid thermal processing (RTP), UV curing with Hg lamps, and recently flash annealing with Xe pulsed lamps are powerful and up-scalable tools for curing, drying, activation, re-crystallization and sintering of various thin film layers and patterns. Depending on the material`s absorption spectrum one can choose an appropriate source and energy. Several photonic systems are available:
- Tunable UV system with 1 kW mercury lamp for wavelength-dependent studies in controlled atmosphere.
- RTP system AS-One 150 system with halogen lamps.
- Photonic curing system PulseForge 1300 with peak radiant power of 24 kW/cm2 (pulse energy up to 45 J/cm2) enabling processing of a wide range of materials starting from printed inks to refractory oxides and semiconductors. As the light pulse is very short, on the order of 20… 20'000 microseconds, a light-absorbing surface is rapidly heated while the substrate bulk remains cold, which enables processing on paper and plastics.