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VERSION:2.0
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X-PUBLISHED-TTL:P1W
BEGIN:VEVENT
UID:69f27c707eb8c
DTSTART:20210211T100000Z
SEQUENCE:0
TRANSP:OPAQUE
DTEND:20210211T130000Z
LOCATION:Online (Teams) and ICFO Auditorium
SUMMARY:ICFO | MEHMET ZAFER AKGUL
CLASS:PUBLIC
DESCRIPTION:Due to the continuously increasing energy demand and the enviro
 nmental concerns about climate changes raised by international community\,
  alternative energy resources have been put under intense investigation fo
 r the past decade. As a consequence\, different technologies have been pro
 posed\, photovoltaics being a promising one among them. Till now\, differe
 nt structures and methods have been employed to fabricate photovoltaics fo
 r energy production. Traditionally\, vacuum-based deposition methods have 
 been used to form the stacks required for proper photovoltaic operation. T
 riggered by the advancements in colloidal synthesis methods\, thin films o
 f colloidal semiconductor nanocrystals (CNCs) have gained tremendous atten
 tion as cheap substitutes for vacuum-deposited layers. Up to date\, variou
 s colloidal synthesis methods have been developed to produce semiconductor
  nanocrystals for applications in photovoltaics. Thanks to the high degree
  of controllability and high material quality\, hot injection methods have
  been the way-to-go for the past decades. However\, the application of CNC
  films in large-scale photovoltaics has been delayed due to the synthesis 
 constraints originating from hot injection methods itself.\nIn this work\,
  we demonstrate that it is possible to eliminate the need for air-free tec
 hniques by careful selection of the precursors and oxygen-aware design of 
 reaction conditions. We use the semiconducting compound silver bismuth sul
 fide (AgBiS2) as the prototype material to demonstrate the easiness and ef
 ficiency of the method. This semiconducting compound is selected as the pr
 ototype material thanks to its attractive optical properties for photovolt
 aics and the environmentally friendly nature of the constituent elements. 
 Solar cells fabricated using CNCs synthesized at room temperature have yie
 lded a power conversion efficiency of 5.5 %\, demonstrating the promising 
 potential of the method. The application of the method in the synthesis of
  AgBiS2 CNCs results in a cost reduction of at least 60 % compared to the 
 previous studies reporting similar photovoltaics-grade AgBiS2 CNCs. Anothe
 r important challenge in employing hot injection methods is the scalabilit
 y. Due to the difficulties in maintaining the thermal fluctuations within 
 the reaction volume low and in the maintenance of inert atmosphere inside 
 the reaction vessel\, hot injection methods impose an inherent scale const
 raint on the synthesis. On the other hand\, with the elimination of scale 
 constraint by the use of an ambient condition synthesis method\, the requi
 rement for high temperature reaction and chemically inert reaction environ
 ment is eliminated\, enabling us to achieve large-scale volume production 
 of CNCs. This\, in turn\, can lower the production cost of CNCs further\, 
 hence the cost of photovoltaics that are based on CNCs. In addition\, we s
 how that the ambient condition method can be adapted for the synthesis of 
 another metal chalcogenide\, namely silver bismuth selenide CNCs (AgBiSe2)
  with an extended absorption spectrum further into the near infrared down 
 to ~ 0.9 eV. The resulting AgBiSe2 CNC solar cells achieved a preliminary 
 efficiency up to 2.6 %. Also\, thanks to the structural similarity of thes
 e two compounds\, the two methods that are developed for the synthesis of 
 AgBiS2 and AgBiSe2 CNCs are combined and optimized to obtain alloyed quate
 rnary AgBiSSe CNCs as a facile means of bandgap tuning in silver bismuth c
 halcogenide semiconductor family. The formation of AgBiSSe CNCs are verifi
 ed through optical and structural characterization methods to show the for
 mation of quaternary phase and also the phase purity of the obtained produ
 ct. Overall\, it is shown that the proposed ambient condition synthesis me
 thod is capable of providing photovoltaics-grade RoHS-compliant materials 
 at a lower cost and higher throughput compared to the hot-injection based 
 methods\, opening a novel way for low-cost environmentally friendly photov
 oltaics.
DTSTAMP:20260429T214728Z
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