We
have successfully substituted trivalent Bi3+ with
divalent Pb2+ in Cs3Bi2Br9-layered perovskites. Controlled heterovalent Pb substitution in
these Cs3Bi2Br9-layered perovskites
reduces the band gap because of the emergence of defect states in
between the bands. These heterovalent Pb-substituted Cs3Bi2Br9 bulk perovskite compounds are successfully
synthesized for the first time by chemical reprecipitation method.
X-ray photoelectron spectroscopy analysis indicate that lead substitution
in the structure is in Pb2+ form, which creates a charge
imbalance in the compound as it replaces Bi3+ from the
layered perovskite structure. Such charge imbalance is compensated
either by bromine vacancies (VBr) or interstitial cesium
(Csi) additions. VBr or Csi in Cs3Bi2Br9 along with PbBi creates
defect states in between the bands, which results in redshift in the
layered perovskite band. Band structure calculations indeed confirm
the onset of such defect states, responsible for the redshift. A more
detailed defect physics simulation indicates that the defect complex
PbBi + VBr is more probable to form if Pb is
rich in the environment, which consequently introduces a few deep
level defects responsible for the reduction of the band gap. Understanding
of the electronic structure and defect physics of such heterovalent
Pb-substituted Cs3Bi2Br9 will strengthen
the future photovoltaic and optoelectronic applications.
Unique mesoporous silicoaluminophosphate (MESO-SAPO-37) with uniform pores (3 nm) was synthesized for the first time by using a faujasite-type microporous SAPO-37 precursor. MESO-SAPO-37 contains hierarchical mesopores with a microporous secondary building unit. It possesses strong acidity and shows high catalytic activity for the conversion of 1-octene, with the exclusive formation of isomerized products (84%).
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