@phdthesis{oai:kyutech.repo.nii.ac.jp:00007279,
 author = {Vats,  Ajendra Kumar},
 month = {2021-09-30},
 note = {1 Introduction to solar cell||2 Experimental （Instrumentation and characterization）||3 Computational molecular design of dyes with varying anchoring groups||4 Influence of the Nature of Anchoring groups on photovoltaic performances and stability||5 Fine-tuning of dyes with Phosphonate anchoring group for improved stability and efficiency||6 General conclusion and future scope||7 Achievements, Natural photosynthesis inspired dye-sensitized solar cell （DSSC） has attracted huge attentions amongst next-generation solar cells owing to their transparency, vivid colors for aesthetic beauty, and very high photo conversion efficiency （PCE） under indoor light conditions. Besides, the cost of fabrication is also envisioned due to the utilization of the low-cost raw materials and processes not demanding for use of high energy. Amongst the next generation, solar cells DSSCs have entered into commercial ventures for the production of solar cell products aiming towards low-end applications. In the last three decades of research and development, DSSCs have witnessed not only very high photon harvesting quantum yield in the visible region （>90%） but also the photo conversion efficiency （PCE） of 12-14 % despite photon harvesting mainly in the 400 nm -700 nm wavelength region. The visible region of the solar spectrum consists of only 45 % of the solar energy while 55 % is still available for energy harvesting. This offers good hope for the design and development of the novel near-infrared （NIR） dyes to have more photon flux harvested leading to further enhancement in the PCE. Besides this, the stability of the DSSCs is another bottleneck towards commercialization, which needs to be solved amicably. My research was started with the design and development of novel sensitizers with different anchoring groups and having the capability of photon harvesting in the far-red to near infra-red （NIR） wavelength region. To investigate the explicit role of the anchoring groups, the main p-molecular framework of the dye was kept the same. Quantum chemical （QC） calculations utilizing the Gaussian G09 program has been used to design novel dyes suitable for DSSCs utilizing mesoporous TiO2 and iodine based redox electrolyte. Several anchoring groups including the most commonly used carboxylic and cyanoacrylic acid were taken into consideration during QC calculations. Selection of the anchoring groups was made considering, mode of binding, the strength of binding, and control of dye aggregation behavior. QC calculation was conducted for the estimation of the energetics of dyes, charge distribution, electron density distribution in the highest occupied molecular orbitals （HOMO） and lowest unoccupied molecular orbital （LUMO）, and electronic absorption. A new approach was proposed to construct a theoretical energy band diagram for the sensitizers, which matches very well with the experimental band diagrams. Based on QC calculations, unsymmetrical squaraine dyes bearing different anchoring groups for their binding on the surface of mesoporous TiO2 were successfully synthesized, characterized, and subjected to photophysical investigations. Implications of the nature of the anchoring group on device performance and stability after DSSC fabrication were investigated in detail. Adsorption behavior of these dyes on the thin films of mesoporous TiO2 was investigated and results indicated that the rate of dye adsorption follows the order −COOH>-PO3H2>OH>SO3H. At the same time, dye desorption studies demonstrated that the stability of adsorbed dyes on the mesoporous TiO2 follows the order -PO3H2> >OH>−COOH>–SO3H. Despite enhanced dye loading, very high binding strength, and favorable energetic cascade, SQ-143 bearing Phosphonic acid exhibited greatly hampered PCE （0.8 %） compared to that of SQ-138 with carboxylic acid anchoring group （4.1%） To address the poor photon harvesting issues of dyes with phosphonate anchoring group despite their very strong binding with TiO2, six unsymmetrical squaraine dyes with varying anchoring groups were rationally designed. A perusal of the binding strength on TiO2 corroborated that SQ-162 bearing double anchoring groups of phosphonic and acrylic acid exhibited >550 times stronger binding as compared to dye SQ-140 bearing cyanoacrylic acid as anchoring group. SQ-140 exhibited the best photovoltaic performance with very good photon harvesting mainly in far-red to NIR wavelength region with PCE of 5.95 % under 1 Sun solar irradiation. Newly designed dye SQ-162 not only solved the problem of very poor efficiency of dye bearing only phosphonic acid while keeping the high dye loading and extremely high binding strength opening the path of design and development of novel NIR dyes with improved efficiency and stability by further extending the π-conjugation of the main dye molecular framework., 九州工業大学博士学位論文 学位記番号：生工博甲第388号 学位授与年月日：令和3年3月25日, 令和2年度},
 school = {九州工業大学},
 title = {Investigation of NIR Dyes with Varying Anchoring Groups Aiming Towards Improved Stability and Efficiency by Rational Molecular Design},
 year = {}
}