PHOTOSENSITIVE SELENIUM NANOPARTICLES TETHERED TO SILICON NANOWIRES FOR SOLAR ENERGY CONVERSION

Maity, Debanjan and Deepa, Melepurath (2019) PHOTOSENSITIVE SELENIUM NANOPARTICLES TETHERED TO SILICON NANOWIRES FOR SOLAR ENERGY CONVERSION. Masters thesis, Indian institute of technology Hyderabad.

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Abstract

This work aims at fabricating different types of liquid junction silicon nanowire solar cells and testing their photovoltaic performance. Se NPs are p-type, visible light responsive electrically conductive material that has been synthesized using a very simple and facile hydrothermal method. The n-type silicon wafers are etched using metal catalyzed electroless etching method to produce SiNWs. The SiNWs because of its several beneficial optical and structural properties is applied as photoanode. 0.05 M Br2 in 8.6 M HBr redox mix is used as electrolyte and carbon fabric as counter electrode. The highly expensive Pt electrode which is reported in previous literature is replaced with robust and highly conductive carbon cloth which reduces the cost of device fabrication. When SiNWs is used as photoanode the solar cell gives an efficiency of 4.91%. But when this SiNWs are modified by dropcasting photoconductive SeNPs over it then 43% rise in efficiency is observed. This rise in efficiency is mainly attributed to the hole transporting property of Se NPs through its c axis of hexagonal crystal structure. This facile hole transportation reduces charge recombination in electrode-electrolyte interface and enhances solar cell performance. The previously reported electrocatalytic metal NPs like Au and Pt are replaced by Se. The expensive Metal nanoparticles like Au and Pt can only act as electron trappers where as SeNPs are hole conductors and thus can rapidly transport the photogenerated holes. These photogenerated holes causes photooxidation and reduces the device performance and stability. But in presence of hole transporting material like Se NPs photooxidation is minimized and device performance is further improved compare to Au nanoparticle decorated SiNWs electrode. To prove this statement a control cell experiment is performed. The results show a 1.5 times rise in efficiency when SiNWs are decorated using Se NPs but for Au NPs the efficiency is almost same as the pristine SiNWs electrode. Optical, structural, PEC, and impedance studies furnish a deep understanding of the phenomena involved in yielding a superior performing liquid-junction PEC solar cell based on the Se NPs@Si NW photoanode.

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