Fabrication And Characterization Of Efficient And Ambient Stable Perovskite Solar Cells

Sun is a paramount source of natural energy which can effectively meet the growing energy demands of modern world.Compared to other fossil energy sources,Sun can provide abundant,clean and cost-effective energy without disturbing natural eco system.To gain maximum benefit from this global source of alternative energy,it is important to develop facile and novel solar energy conversion techniques,which can ensure maximum output power at limited cost.Solid state photovoltaic cells have been emerged as potentially most suitable candidate for conversion of solar energy.Since last one decade,perovskites have been surfaced as one of most outstanding class of solar energy harvesting materials.The tremendous photovoltaic strength of perovskites is obvious from their rapidly growing power conversion efficiency(PCE)which already surpassed a remarkable value of 25%.The swift increase in PCE of perovskites is a result of intense research and development efforts which produced tailored perovskite molecular structures,facile fabrication techniques,novel device structures,specialized hole and electron transport materials.Potentially perovskites are now right at the place where they can challenge the commercial dominance of widely implemented silicon based inorganic solar cells.In this dissertation,two important research directions related to hole transporting materials with intrinsically superior PCE and effect of surface engineering of perovskite layer on various performance parameters of perovskite solar cells have been explored in detail.Performance of hole transporting material(HTM)plays a fundamental role in estimating overall efficiency of perovskite solar cell(PSC).Hygroscopic dopants employed to boost the PCE of PSCs strongly degrades their long-term ambient stability,hence limiting their commercial application specially in humid conditions.Dopant free HTMs with high intrinsic hole mobility and stability have been emerged as a fascinating choice for production of highly efficient and ambient stable PSCs.Organo-sulfur tetrathiafulvalene(TTF)based small molecular materials have attained remarkable attention due to their intrinsically higher hole transporting properties.So,facile synthesis and implementation of a novel TTF derivative as a dopant free HTM for fabrication of efficient and ambient stable PSC has been discussed in detail.The PSC based on dopant free TTF HTM showed remarkable photovoltaic efficiency of 15.66% which is one of highest value for any TTF based HTM.Beside efficiency,PSC based on TTF HTM showed only 16% decline in initial efficiency even after 45 days storage in ambient conditions without any encapsulation which verifies its excellent ambient stability and hydrophobicity.Furthermore,various physical,electrochemical,photovoltaic and optical parameters of TTF HTM are investigated by highly specialized characterization tools.These experimental outcomes proved the remarkable ability of synthesized TTF based HTM to effectively address ambient stability issues related to PSCs without largely compromising PCE.Morphology of perovskite film plays a key role in predicting the overall performance of perovskite solar cells(PSCs).The performance of PSCs strongly degrades due to excessive grain boundaries,uneven and poor surface coverage of perovskite film,antisite defects evolved from bulk or interfacial regions.Post growth passivation by alkylated halides molecules is proved an effective technique to improve crystallinity and reduce defects of perovskite films.In this research,butyl ammonium iodide(BAI)has been employed as a passivating agent to overcome surface defects and traps of cesium doped triple cation perovskite film.It has been noticed that BAI treatment remarkably improved performance and quality of perovskite film and as a result BAI treated planar PSC showed a higher power conversion efficiency(PCE)of over 20 %.Beside efficiency,passivation also proved beneficial in suppressing hysteresis which is obvious from lower hysteresis index of passivated device(0.037)as compared to pristine device(0.060).The probable molecular interaction between perovskite and BAI passivating layer has been analyzed through density functional theory(DFT)calculations.Beside efficiency,post deposition surface passivation also enhanced the ambient stability,obvious from only 17 % decline in initial PCE value of passivated PSC even after 80 days storage in ambient conditions.The detailed structural,morphological,optical,and electrochemical analysis proved that surface passivation of perovskite layer is an effective technique to improve the performance of PSCs.