Transition Metal Doped ZnS Based Photoactive Nanohybrid Material: Synthesis, Characterization and Applications in Hybrid Solar Cell

Abstract

The thesis is divided into three chapters. Chapter 1 presents the background and surveys the current literature and also describes the principles behind the operation of PV devices. Chapter 2 presents the research methods and measurement techniques used in the study. Chapter 3 describes results and discussion and has six different sections. The first section comprises of the synthesis of zinc sulphide (ZnS) and Cd-doped ZnS nanoparticles, Zn1-xCdxS (x= 0.2-0.5), by wet chemical method. Optical, electrical and photovoltaic properties of the nanoparticles were investigated. A significant bathochromic shift of absorption band with respect to the un-doped zinc sulphide was noticed by increasing the cadmium concentration in the doped samples. Consequently, the band gap was tuned into the visible region. XRD analysis showed that the material existed in cubic crystalline state. The conductivity of the doped material, though progressively increasing step by step, was found lower than un-doped ZnS at cadmium contents ranging from 0.2 to 0.4 M but at the highest dopant concentration (Cd, 0.5 M) the conductivity attained a value higher than undoped ZnS by 1.21 × 10-5 Ω-1m-1. The overall % ɳ of the solar cell at 0.5 M Cd content in doped ZnS nanoparticles was found to be 2.33 times higher than the reference device (P3HT-ZnS) (Paper published in Journal of Photochemistry and Photobiology A: Chemistry). The second section describes the influence of dopant concentration on structural, optical and photovoltaic properties of Cu-doped ZnS nanocrystals. A significant blue shift of absorption band with respect to the un-doped zinc sulphide was sighted by increasing the Cu concentration in the doped sample with decreasing the size of nanoparticles. The synthesized nanomaterial in combination with P3HT, poly (3-hexyl thiophene) was worked in the fabrication of solar cells. The overall power conversion efficiency of the solar cell at 0.1 M Cu content in doped ZnS nanoparticles was found to be 1.6 times higher than the reference device (P3HT-ZnS), (Paper published in European Physical Journal Applied Physics). XXIV Furthermore, the third section depicts the synthesis, characterization and photovoltaic performance of Mn-doped ZnS nanocrystals. The PL emission centered at 596 nm is the characteristics emission of Mn2+ which can be attributed to a 4T1→6A1 transition within the 3d shell. The devices with ZnS nanocrystals showed an efficiency of 0.48% without annealing and 0.52% with annealing. By doping with manganese, the efficiency was enhanced by a factor of 0.52 without annealing and 0.59 with annealing. The morphology and packing behavior of blend of nanocrystals with P3HT were studied using Atomic Force Microscopy (Paper published in Optical Materials). Additionally, section fourth describes the effects of embedding un-doped and Mn-doped ZnS nanoparticles in the active layer on the performance of organic photovoltaics devices. The active layer primarily consists of various ratios of the organic electron donor poly (3-hexylthiophene (P3HT) and the electron acceptor [6, 6] phenyl-C61-butyric acid methyl ester (PCBM) together with nanoparticles dissolved in dichlorobenzene. The weight ratio of PCBM to un-doped and doped nanoparticles in the blend was varied, keeping the ratio of P3HT constant. The power conversion efficiency (PCE) improved by increasing the nanoparticle concentration in the active layer blend. The devices with ZnS nanocrystals (1:0.5:0.5) showed an efficiency of 2.42%. By doping with manganese, the efficiency was enhanced by a factor of 1.46 (Paper published in European Physical Journal Applied Physics). However, fifth section describes first time the direct observation of the nucleation and growth process of CdS nanowires by stirring of CdS nanoparticles. The growth process of CdS nanowires consist of three steps, the growth of CdS particles, nucleation of CdS nanorods and finally the growth of CdS nanowires. This method brings forward a new idea to synthesize nanowires. Furthermore, carboxylic functionalize porphyrin was examined as sensitizer for CdS nanowires. The hybrid devices were fabricated with organic polymer with different concentration of dyes and the device with optimum concentration 6×10-6 M shows the highest efficiency of 0.5% with short-circuit current density 3.10 mAcm-2, opencircuit voltage 0.44 V and fill factor 0.37 (Paper published in European Physical Journal Applied Physics). Last section of chapter 3 illustrates photocatalytic degradation of Alizarin Red S using ZnS and cadmium doped ZnS nanoparticles under unfiltered sunlight. Photo catalytic XXV degradation of Alizarin Red S (ARS) by the nanoparticles showed that the cadmium doped ZnS acted as a potential Photocatalyst under unfiltered solar light. The ARS dye was degraded about 50% and 96.7% in the presence of ZnS and Cd-ZnS (Cd, 0.5 M) nanoparticles respectively in 120 min. Furthermore the effect of various parameters, i.e., Photocatalyst concentration, dye concentration, and pH of the solution on the percentage of degradation was also studied. Degradation followed first order kinetics (Paper published in Surfaces and Interfaces).