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UID:69d2561855085
DTSTART:20230322T090000Z
SEQUENCE:0
TRANSP:OPAQUE
LOCATION:Auditorium and Online (Teams)
SUMMARY:ICFO | SHANTI MARIA LIGA 
CLASS:PUBLIC
DESCRIPTION:The availability of energy is a fundamental ingredient for the 
 development of society. However\, the intense consumption of fossil fuels 
 as an energy resource since the second industrial revolution has caused a 
 massive increase in the concentration of CO2 and other greenhouse gases in
  the atmosphere\, which is nowadays known to be the first cause of climate
  catastrophe. For this reason\, it has become a priority to replace fossil
  fuels with more sustainable sources\, which are renewable and produce low
  greenhouse gas emissions. Photovoltaics is one of the suitable technologi
 es to carry out this fast transition because it is already well-developed 
 and is based on the use of the infinite energy source\, the Sun. However\,
  increasing the efficiency of solar light conversion into electricity and 
 reducing the cost of photovoltaic devices is fundamental to achieve the go
 als set by policy makers. Consequently\, the development of novel optoelec
 tronic materials\, based on abundant and environmentally friendly elements
 \, is one of the fundamental scientific advances needed to boost the shift
  towards a low-carbon society.\nPerovskites\, whose solar cells reached th
 is year a certified record efficiency of 25.7%\, are the first solution-pr
 ocessed materials to outperform multicrystalline and thin-film silicon and
  therefore one of the most interesting new materials for photovoltaic appl
 ications. In spite of their astonishing performances in solar cells\, the 
 most promising perovskites contain lead\, which is toxic for human beings 
 and potentially a threat to the environment. Hence\, over the last decade\
 , there has been intensive research on strategies to replace lead in the p
 erovskite structure with nontoxic elements. Among all the novel perovskite
 s studied\, titanium-based vacancy-ordered double perovskites demonstrated
  one of the most promising performances when applied in solar cells.\nThis
  thesis focuses on the development of new solution syntheses for the prepa
 ration of novel lead-free vacancy-ordered double perovskite nanocrystals b
 ased on titanium and tin in the oxidation state +4\, which are nontoxic an
 d abundant elements. All the synthesized perovskite nanocrystals were char
 acterized structurally\, chemically and optically. Moreover\, the experime
 ntally observed optical properties and the stabilities of these materials 
 were further confirmed by ab initio density functional theory calculations
 .\nWe initially developed a colloidal synthesis to prepare mixed bromide-i
 odide Cs2TiBr6&minus\;xIx perovskites. All these materials are intrinsical
 ly stable with bandgaps in the visible region\; suitable for solar cell ap
 plications. However\, they showed very high instability in air\, which pre
 vented their application in devices and that motivated us to search for st
 rategies to stabilize them.\nEncouraged by the higher reported stabilities
  of Sn+4 perovskites with the same vacancy-ordered double perovskite struc
 ture\, we synthesized pure tin halide perovskite NCs and novel mixed titan
 ium/tin iodide and bromide perovskite NCs. The experiments confirmed that 
 tin perovskites are stable in air and that the mixtures with the highest a
 mount of tin in the structure are stable in air for longer than pure titan
 ium perovskites. Finally\, for the case of Cs2TiBr6\, we developed a room 
 temperature method to reach comparable stabilities in air through a surfac
 e treatment with tin compounds.\nIn summary\, we have developed a low-temp
 erature solution method for the preparation of novel environmentally-frien
 dly perovskites based on tin and titanium and studied their properties for
  the first time\, both computationally and experimentally. Finally\, we ha
 ve found a way to increase the stability in air of titanium-based perovski
 tes through the addition of tin in the structure. Overall\, this thesis pr
 ovides an insight into novel lead-free perovskites based on titanium and t
 in and it represents a milestone for the understanding and development of 
 this new class of materials.
DTSTAMP:20260405T123120Z
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