Metal Nanostructures in Photoanodes and Counter Electrodes for Cadmium Sulfide Based Quantum Dot Solar Cells

P, Naresh Kumar (2017) Metal Nanostructures in Photoanodes and Counter Electrodes for Cadmium Sulfide Based Quantum Dot Solar Cells. PhD thesis, Indian Institute of Technology Hyderabad.

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Abstract

The possibility of attaining power conversion efficiencies (PCE s ) higher than theoretical efficiencies (as dictated by the Shockley Queisser’s limit), cost - effective components, and ease of fabrication have rendered quantum dot solar cells (QDSCs) to be as attractive as their counterparts among third generation solar cells such as organic solar cells and dye sensitized solar cells . In this thesis, CdS QDs were chosen as the primary light harvesters due to ease of synthesis, high absorption coefficient, and their good chemical compatibility with the sul fide electrolyte that is widely used as the hole transport layer in QDSCs. The photoanode architecture was modified by using different metal nanostructures, and plasmonic and light scattering effects of these nanostructures were tapped to improve the perfo rmance of QDSCs. A photoanode architecture comprising of C dSeS alloy QDs , CdS , Au nanoparticles (NPs) capped with poly ( acrylic acid ) (PAA) and C 60 ; all anchored to TiO 2 , delivered a PCE of 3.6% under 1 s un illumination. In the next work, the PCE of a TiO 2 /CdS photoanode was improved via plasmonic enhancement and increased electrical conductivity imparted by the addition of Ag nanorods and NPs. I n the same work , a novel gel electrolyte containing sulfide and fumed silica was prepared and applied to QDSCs. T he maximum PCE achieved in this work was 4.27%. In these two studies, functionalized multiwalled carbon nanotubes (MWCNTs) were used as the counter electrode s (CE s ). In the subsequent study, C u nanoneedles were incorporated in the TiO 2 /CdS photoanode , and by using a low cost, highly conducting C - Fabric as the CE, a PCE of 4.36 % was achieved. In another work, in order to enhance the span of plasmonic absorption, AuAg alloy NPs were used in the TiO 2 /CdS photoanode and a PCE of 4.94% was obtained for the champion cell. Besides the photoanode, the CE also controls the PCE of a QDSC, and therefore, an elaborate study on identifying the best CE for a TiO 2 /CdS based cell was undertaken by studying 14 different CEs. A C - Fabric/WO 3 - x compos ite was identified to be the best CE on the basis of its’ high electrocatalytic activity for polysulfide reduction , low reduction over potential and l east charge transfer resistance. In the final work, with the superior C - Fabric/WO 3 - x as CE, a polysulfide g el as the electrolyte and a T i O 2 (carbonate treated) /CdS/Au @PAA as the photoanode , PCEs of 4 .32 and 1.06% were achieved for 1 and 4 cm 2 c ells. S tability studies of QDSCs under continu ous illumination and dark storage were also performed. This thesis gives a comprehensive understanding of (i) the role played by metal nanostructures in improving the performance of the photoanode, (ii) the effect of CE on the PCE of a QDSC, and (iii) the factors that control the stability of QDSCs

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