Design and fabrication of advanced functional materials for electrochemical sensor and photovoltaic applications

Abstract

The Investigations embodied in thesis entitled “DESIGN AND FABRICATION OF ADVANCED FUNCTIONAL MATERIALS FOR ELETCROCHEMICAL SENSOR AND PHOTOVOLTAIC APPLICATIONS” was initiated in May 2015 in the Discipline of Chemistry, Indian Institute of Technology Indore, Indore, 453552, India. The objectives of this thesis are to design and fabrication of advanced functional materials for the construction of electrochemical sensor and photovoltaic applications. The focal points of thesis work are as follows- 1. Design and synthesis of different electrode materials and light absorbers. 2. Advanced characterization techniques have been employed to understand their physio-chemical and optoelectronic properties. 3. Fabrication of electrodes for nitro sensing and photovoltaics. 4. Investigating the performance of the electrodes for nitro sensing and photovoltaics. This thesis consists of eight chapters which include general introduction to nitro sensing and photovoltaics based on different nanostructured electrode/light absorber materials (Chapter 1) followed by the synthesis of different electrode materials (Chapter 2-3) and light absorbers and their applications to sensor and photovoltaics (Chapter 4-7). This thesis outlines the future perspective in the Chapter 8. In Chapter 1 (General Introduction), the basic of transition metal oxide based nanomaterials for electrochemical sensors have been discussed. The recent advances in nitroaromatic sensors and their challenges have been provided. Furthermore, the origins of perovskite solar cells, fundamental concepts, working principle and challenges have been discussed. Moreover,the finding of lead (Pb) free perovskites and their optoelectronic properties for photovoltaic applications and future aspects have been discussed with recent literature. In Chapter 2, a perovskite (SrTiO3) and reduced graphene oxide (rGO) based nanocomposite (rGO/SrTiO3) material has been synthesized in-situ. The rGO/SrTiO3 nanocomposite was characterized by PXRD, SEM, EDX mapping, TEM and SAED pattern to confirm its purity and morphology. The surface of the glassy carbon electrode (GCE) was modified by coating rGO/SrTiO3 nanocomposite without any binder. This modified electrode GCE-rGO/SrTiO3 (MGCE) was employed for electrochemical detection of nitro-substituted aromatics such as p-nitrophenol (p-NP), 2,4-dinitrophenol (2,4-DNP), 2,4-dinitrotoluene (2,4-DNT) and 2,4,6-trinitrophenol (TNP) which shows a rapid electronic communications. The MGCE exhibited the limit of detection (LOD) of 110nM, 134nM, 128nM, 146nM, high sensitivity of 193.43 μA μM-1 cm-2, 25.34 μA μM-1 cm-2, 71.66 μA μM-1 cm-2, 13.16 μA μM-1 cm-2 and a linear range between 0.3-0.8, 0.4-0.7, 0.5-0.8, 0.5-0.7 μM for p-NP, 2,4-DNP, 2,4-DNT and TNP, respectively. The developed MGCE sensor thus implemented is also advantageous for its lowcost, stability, reliability and rendering applications for real system analysis. In Chapter 3, α-MnO2 nanorods were synthesized by facile hydrothermal method. The synthesized α-MnO2 nanorods were characterized by PXRD, UV-Vis, SEM, EDX mapping, TEM and SAED pattern to confirm their purity and morphology. Furthermore, active surface area of the glassy carbon electrode (GCE) was modified by α-MnO2 nanorods (GCE/α-MnO2) which showed a rapid sensitivity towards p-nitrotoluene (p-NT), 2, 4-dinitrotoluene (DNT) and 2, 4, 6-trinitrophenol (TNP) with distinct cathodic peaks. The GCE/α-MnO2 exhibited the limit of detection (LOD) of 144 nM, 133 nM, 100 nM and a high sensitivity of 17.6 μAμM-1cm-2, 22.6 μAμM-1cm-2, 54.82 μAμM-1 cm-2 for p-NT, DNT and TNP, respectively.In Chapter 4, we developed a highly stable planar heterojunction perovskite solar cell (PSC) with a novel architecture (ITO/GO/PEDOT:PSS/MAPbI3/PCBM/Carbon tape). The PSC was developed under atmospheric conditions using GO/PEDOT:PSS as hole transport layer and carbon tape as back contact. The fabricated device shows good stability and performance with a power conversion efficiency of 5.2%. The fabricated devices were exposed to ambient condition for 96 h which shows excellent stability. Remarkably, we found that the stability of the planar heterojunction perovskite solar cell was attributed to the presence of GO which inhibits the direct contact between PEDOT:PSS and MAPbI3. In Chapter 5, we report design and synthesis of a one dimensional (1D) polymeric chain of methyl ammonium bismuth chloride perovskite. In a simple synthetic strategic route, the 1D-polymeric chain of [(CH3NH3)3Bi2Cl9]n (1) was prepared by slow diffusion of the methanolic solution of BiCl3 into aqueous solution of CH3NH3Cl at room temperature (Scheme 1). The synthesized 1 was further authenticated by single crystal x-ray diffraction (SCXRD) studies. Moreover, the proposed combination of the fabricated lead free perovskite solar cells with a novel device architecture (ITO/BL-TiO2/Meso-TiO2/[(CH3NH3)3Bi2Cl9]n/Spiro-MeOTAD/Au) was employed. The fabricated PSCs device showed the excellent open circuit voltage of 430 mV. We believe that the efficiency and open circuit voltage could be improved by developing fabrication methods, optimizing films thickness, solvent engineering, employing different architectures or new hole/charge extraction materials. Moreover, 1 had a band gap of 2.85 eV and a polymeric structure which suggest its potential for tandem solar cells, photodetectors, LEDs, batteries and super-capacitors. In Chapter6, we have developed high performance lead free PSCs by employing a modified two-step deposition method with FTO/CL-TiO2/m-TiO2/MBI/Spiro-MEOTAD/Au device architecture. The PSCs device fabricated by two-step deposition method has shown good power conversionefficiency of 0.41% along with high open circuit voltage of 870 mV and found to be highly stable up to 60 days under atmospheric conditions (humidity ~40-50%). The film quality of the MBI was found to be superior by introducing modified two-step deposition method over one-step deposition. In Chapter 7, we have employed a highly stable copper (Cu) based perovskites (C6H4NH2CuBr2I and C6H4NH2CuCl2I) as light absorbers towards the development of Pb free PSCs. These perovskite light absorber has advantages over bismuth based light absorbers in terms of optoelectronic properties as well air and water resistant ability. These light absorbers were further employed to develop the Pb free perovskite solar cells. The fabricated devices showed good efficiency of 0.63% which is higher than most of the Pb free perovskite solar cells. TheChapter 8 outlines the conclusions and future perspectives of this work.