Special Seminar

Electronically Passivated Hole-Blocking Titanium Dioxide/Silicon Heterojunction for Hybrid Silicon Photovoltaics

Tue, 09 Feb 2016
Special Seminar
Gabriel Man
Electrical Engineering, Princeton University
Electronically Passivated Hole-Blocking Titanium Dioxide/Silicon Heterojunction for Hybrid Silicon Photovoltaics
Feb 09, 2016


There is considerable interest in titanium oxide/dioxide (TiOX/TiO2) based electron-selective, hole-blocking heterojunctions due to their applications in organic 1 and inorganic photovoltaics 2, and organic light-emitting diodes. In this work, a low temperature (< 100 °C) chemical vapor deposition (CVD) technique is used to deposit ultra-thin (n-type) TiO2 layers onto hydrogen-passivated surfaces of crystalline silicon (c-Si). Energy level alignment and chemical composition at these abrupt, interfacial layer-free TiO2/Si heterojunctions are investigated via ultra-violet, X-ray and inverse photoemission spectroscopy (UPS, XPS, IPES), for c-Si doping ranging from p++(1019) to n++(1019). The interface Fermi level position and device-relevant TiO2/Si band offsets are found to shift monotonically as a function of the Si doping, revealing the absence of Fermi level pinning at the c-Si interface and pointing to simple Fermi level equilibration as the driving mechanism behind the interface energy level alignment. Electrical transport measurements performed on TiO2/Si-based diodes confirm the energy level alignment yielded by spectroscopic measurements and the hole-blocking properties of the TiO2/Si heterojunction, exclude hole conduction in the TiO2 as a transport mechanism, and show carrier recombination at the TiO2/p-Si heterojunction.

1. Kim, H. et al. Investigation of ultra-thin titania films as hole-blocking contacts for organic photovoltaics. J. Mater. Chem. A 18–28 (2015).

2. Nagamatsu, K. A. et al. Titanium dioxide/silicon hole-blocking selective contact to enable double-heterojunction crystalline silicon-based solar cell. Appl. Phys. Lett. 106, 123906 (2015).




Gabriel Man is a Ph.D. candidate in Electrical Engineering at Princeton University, under the supervision of Professor Antoine Kahn.  He is passionate about solving global-scale problems – such as generating energy sustainably and transmitting/storing it efficiently – through fundamental and applied research in electronic materials.  Gabriel received his B.A.Sc. and M.A.Sc. (co-advised by Professors Konrad Walus and Boris Stoeber) from UBC in Electrical & Computer Engineering.   He is a former NSERC Ph.D. fellow.