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SUMMARY:Combination of transient and steady-state photoluminescence for th
 e characterization of halide perovskite-based layer stacks - Thomas Kircha
 rtz\; Forschungszentrum Julich GmbH
DTSTART:20191029T140000Z
DTEND:20191029T153000Z
UID:TALK134017@talks.cam.ac.uk
CONTACT:Elizabeth Tennyson
DESCRIPTION:Both transient and steady state photoluminescence PL have been
  frequently used to analyze the properties of halide perovskite films[1] a
 nd recently also layer stacks\, i.e. films with interfaces.[2-4] Here\, we
  present our current level of understanding of how to analyze the data. In
  the case of films\, long decays in transient PL correlate well with stron
 g steady state PL. The shape of the decays allows us to determine bimolecu
 lar and monomolecular recombination coefficients\, the former of which is 
 clearly affected by photon recycling.[1\, 5] In the case of films with one
  interface\, we show that high luminescence is still beneficial for high o
 pen-circuit voltages in devices and still correlates with long photolumine
 scence decays.[2] We show by simulation how the combination of steady stat
 e PL with tr-PL can be used to better understand band alignment at interfa
 ces and how it provides an estimate of the surface recombination velocitie
 s. Finally\, we discuss the case of layer stacks with two contacts and of 
 full devices. Here\, additional effects such as the conductivity and capac
 itance of contact layers become important. In addition\, the question aris
 es on how to compare purely optical techniques with techniques that use el
 ectrical detection. One example is the comparison between transient PL and
  and transient photovoltage. The difference between the two is that transi
 ent PL measures the internal voltage\, i.e. the quasi-Fermi level splittin
 g\, and transient photovoltage measures the external voltage that builds u
 p at the external terminals of the cell. While both decays are affected by
  the contact layers\, the impact is substantially different. The external 
 voltage first has to be built up by charging up the capacitance of the int
 erfacial layers\, the internal voltage peaks immediately after the laser p
 ulse and then decays fairly quickly. 
LOCATION:Raleigh Seminar Room\, Maxwell Centre\, Cavendish Laboratory
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