Cheng Chieh Chao

Solid oxide fuel cell with corrugated thin film electrolyte

A low temperature micro solid oxide fuel cell with corrugated electrolyte membrane was developed and tested. To increase the electrochemically active surface area, yttria-stabilized zirconia membranes with thickness of 70 nm were deposited onto prepatterned silicon substrates. Fuel cell performance of the corrugated electrolyte membranes released from silicon substrate showed an increase of power density relative to membranes with planar electrolytes. Maximum power densities of the corrugated fuel cells of 677 mW/cm2 and 861 mW/cm2 were obtained at 400 and 450 degrees C, respectively.

Enhanced Oxygen Exchange on Surface-Engineered Yttria-Stabilized Zirconia

Ion conducting oxides are commonly used as electrolytes in electrochemical devices including solid oxide fuel cells and oxygen sensors. A typical issue with these oxide electrolytes is sluggish oxygen surface kinetics at the gas-electrolyte interface. An approach to overcome this sluggish kinetics is by engineering the oxide surface with a lower oxygen incorporation barrier. In this study, we engineered the surface doping concentration of a common oxide electrolyte, yttria-stabilized zirconia (YSZ), with the help of atomic layer deposition (ALD). On optimizing the dopant concentration at the surface of single-crystal YSZ, a 5-fold increase in the oxygen surface exchange coefficient of the electrolyte was observed using isotopic oxygen exchange experiments coupled with secondary ion mass spectrometer measurements. The results demonstrate that electrolyte surface engineering with ALD can have a meaningful impact on the performance of electrochemical devices.

Energy transfer between quantum dots of different sizes for quantum dot solar cells

Exciton recombination and slow charge carrier transport, major limitations of advanced photovoltaic cells, may be mitigated by designing cells with strong electric fields in the active regions. This may be done by combining quantum dots (QDs) of different Fermi levels in close proximity. While previous reports of quantum dot solar cells utilizing QDs of different sizes indicate that electrons and holes are transferred together from large bandgap QDs to small bandgap quantum dots, lowering the efficiency of the solar cell, we report a mechanism that may be able to use different bandgap QDs to split excitons and drive charge carrier transport, increasing the efficiency of solar cells. Quantum simulations of band structures of QDs show indications of this behavior, and experiments on solar cells with quantum dots of different sizes separated by thin insulating layers show improved photocurrent compared to solar cells with QDs of the same size.