Fabrication of axial p-n junction silicon nanopillar devices and application in photovoltaics

•Si nanopillar fabrication by cryogenic plasma etching after colloidal lithography•Axial p-n junction Si nanopillar photovoltaic device fabrication•Study of electrical passivation, and demonstration of low reflectance.•A fill factor of 0.59 was investigated for axial Si pillar PV device.•Promising performance of the proposed recipe to fabricate next generation PV cells

A photovoltaic device based on plasma-etched silicon nanopillar (SiNP) arrays is demonstrated. Highly ordered, aligned and perpendicular to the substrate pure crystalline silicon nanopillars, that follow the axial p-n junction geometry, are fabricated by polystyrene colloidal particle self-assembly followed by cryogenic silicon plasma etching. The SiNPs surface electrical passivation by both methyl termination and hydrogen termination is examined and the encapsulation of the pillars by PMMA and transparent conductive oxide is demonstrated. The total reflectance (both specular and diffuse) of SiNP arrays of different period and diameter is measured. The total reflectance of silicon is reduced significantly in a wide range of the optical spectrum. Electrical characterization of bundles of nanowires was performed in terms of I-V measurements under light illumination. A short-circuit current density (Jsc) of 18.9 mA/cm2, an open-circuit voltage (Voc) of 367 mV and a fill factor (FF) of 0.59 were obtained on such axial p-n SiNP array photovoltaic devices.

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