Dominic Gerlach was awarded the Student Award of the 38th IEEE Photovoltaic Specialists Conference held in Austin, Texas last week. The IEEE PVSC is the premier technical conference in the USA, covering all aspects of PV technology from basic material science to installed system performance and bringing together PV scientists and engineers from throughout the PV industry.
Dominic presented the results of his fundamental study of the electronic structure of the ZnO:Al/a-Si:B interface. These experiments were performed by the Helmholtz-University Young Investigator Group "Interface Design" in close collaboration with the silicon thin-film solar cell experts from the Forschungszentrum Jülich (group of J. Hüpkes) and HZB's Institute for Silicon Photovoltaics (Prof. B. Rech), the material scientists from the National Institute for Materials Science (Tsukuba, Japan; group of M. Sumiya), and the hard x-ray spectroscopy experts from SPring-8 (Hyogo, Japan; H. Yoshikawa) and BESSY II (M. Gorgoi).
In particular, Dominic investigated the valence band alignment of the ZnO:Al/a-Si:B interface – a crucial contact in silicon p-i-n solar cells – by hard x-ray photoemission spectroscopy (HAXPES). Using a combination of different x-ray excitation energies and deliberate sample design he was able to draw a complete “depth-resolved” picture of the chemical and electronic interface structure. Most importantly, he could show that current transport – which takes place via tunneling across the ZnO:Al/a-Si:B interface – is inhibited by a rather large tunnel barrier. In comparison, he showed that the tunnel barrier at the ZnO:Al/mc-Si:B interface is significantly smaller and is the likely source of the improvements in cell performance that occur when a microcrystalline p-type Si buffer is deposited between ZnO:Al TCO and a-Si:B absorber. Thus, Dominic’s work unraveled the electronic structure of a poorly performing contact, laying the basis for a future knowledge-based optimization of the ZnO/Si contact. In recognition of the quality and impact of this work, Dominic’s conference proceedings paper was one of the small number selected by the conference organizers for submission to the IEEE’s peer-reviewed “Journal of Photovoltaics.”