KEYWORDS: Solar energy, Silicon, Solar cells, Photovoltaics, Dye sensitized solar cells, Solid state electronics, Electrodes, Etching, Interfaces, Silicon solar cells
This work will discuss our recent advances focused on integrating high power energy storage directly into the native materials of both conventional photovoltaics (PV) and dye-sensitized solar cells (DSSCs). In the first case (PV), we demonstrate the ability to etch high surface-area porous silicon charge storage interfaces directly into the backside of a conventional polycrystalline silicon photovoltaic device exhibiting over 14% efficiency. These high surface area materials are then coupled with solid-state ionic liquid-polymer electrolytes to produce solid-state fully integrated devices where the PV device can directly inject charge into an on-board supercapacitor that can be separately discharged under dark conditions with a Coulombic efficiency of 84%. In a similar manner, we further demonstrate that surface engineered silicon materials can be utilized to replace Pt counterelectrodes in conventional DSSC energy conversion devices. As the silicon counterelectrodes rely strictly on surface Faradaic chemical reactions with the electrolyte on one side of the wafer electrode, we demonstrate double-sided processing of electrodes that enables dual-function of the material for simultaneous energy storage and conversion, each on opposing sides. In both of these devices, we demonstrate the ability to produce an all-silicon coupled energy conversion and storage system through the common ability to convert unused silicon in solar cells into high power silicon-based supercapacitors. Beyond the proof-of-concept design and performance of this integrated solar-storage system, this talk will conclude with a brief discussion of the hurdles and challenges that we envision for this emerging area both from a fundamental and technological viewpoint.
We demonstrate the operation of a graphene-passivated on-chip porous silicon material as a high rate lithium ion battery anode with over 50x power density and 100x energy density improvement compared to identically prepared on-chip porous silicon supercapacitors. We demonstrate this Faradaic storage behavior to occur at fast charging rates (1-10 mA/cm2) where lithium locally intercalates into the nanoporous silicon, but not underlying bulk silicon material. This prevents the degradation and poor cycling performance that is commonly observed from deep storage in bulk silicon materials. As a result, this device exhibits cycling performance that exceeds 10,000 cycles with capacity above 0.1 mAh/cm2, without notable capacity fade. This work demonstrates a practical route toward high power, high energy, and long lifetime all-silicon on-chip storage systems relevant toward integration of energy storage into electronics, photovoltaics, and other silicon-based technology.
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