Connecting wire-based solar cells without any transparent conducting electrode

In order to reduce substrate costs and increase light absorption, solar cells based on semiconductor wire arrays are currently being actively studied. Whether built with Si, InP or other semiconductor materials, wire-based cells invariably use a transparent conductive coating for one of the electrodes, which complicates the processing and does not contribute to the reduction of the overall cost of the cell. Here, we propose a totally novel connection process, where the transparent conductive electrode is replaced with an array of in situ grown metallic nanowires. During their growth, these metallic nanowires randomly connect to core-shell p-i-n Si wires previously synthesized by chemical vapor deposition. We demonstrate the feasibility of this new random connection concept by using a coplanar solar cell design with interdigitated base and emitter contacts. We obtain a high fill factor of similar to 74% and efficiencies of 4.5% with only 33% of the surface covered by p-i-n Si wires. © The Royal Society of Chemistry 2016101sciescopu

Highly interconnected Si nanowires for improved stability Li-ion battery anodes

Silicon exhibits the largest known capacity for Li insertion in anodes of Li-ion batteries. However, because of large volume expansion/phase changes upon alloying, Si becomes powder-like after a few charge-discharge cycles. Various approaches have been explored in the past to circumvent this problem, including the use of nanomaterials, particularly Si nanowires. However, even though nanowires resist cracking very well, anodes based on Si nanowires still see their original capacity fade away upon cycling, because of wire detachment from the substrate, due to the stress generated at their roots upon alloying with Li. Here, we present a silicon nanowire growth strategy yielding highly interconnected specimens, which prevents them from being individually detached from the substrate. We report a ∼ 100% charge retention after 40 cycles at C/2 rate, without charging voltage limitation. We also show that our anodes can be cycled at 8C rates without damage and we grow nanowires with a density of 1.2 mg/cm 2, yielding anodes delivering a 4.2 mAh/cm 2 charge density. Finally, we point out that a better understanding of the interactions of silicon with electrolytes is needed if the field is to progress in the future. © 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim