Time-resolved photoluminescence (PL) by time correlated single photon counting (TCSPC)

(possible with selected excitation wavelength and sample ambient as required)

PL decay is extremely important information and relevant to most essential carrier dynamic processes. Such PL decay measurement has been proven to be very useful for the information of materials/nanocomposites/devices for electron-hole recombination (radiative and nonradiative), defect trapping and surface trapping (surface passivation), charge transfer and carrier transport etc. Therefore, such techniques have been intensively applied for characterization of new materials and devices, determination the quality of the materials or devices and surface passivation, determination of the photogenerated charge transfer and carrier transport. Particularly useful for new materials, nanomaterials and nanocomposites for photovoltaics, photocatalysis, photonics and biomaterials etc.

Measurement Time-resolved PL by TCSPC

Examples of time-resolved PL for applications in photovoltaics and nanomaterials

References

  • Chen et al. Spatial Distribution of Lead Iodide and Local Passivation on Organo-Lead Halide Perovskite, ACS applied materials & interfaces 9 (2017), 6072-6078
  • Wen et al. Mobile charge-induced fluorescence intermittency in methylammonium lead bromide perovskite, Nano letters 15 (2015), 4644-4649
  • Wen et al. The Role of Surface Recombination in Halide Perovskite Nanoplatelets, ACS applied materials & interfaces, 10, 31586-31593 (2018) (IF8.097)
  • Zhang et Chemical Dopants Engineering in Hole Transport Layer for Efficient Perovskite Solar Cells: An Insight into the Interfacial Recombination, ACS Nano, 12, 10452-10462 (2018) (IF13.709)

Ultrafast (fs-ps) transient absorption and time-resolved PL

Ultrafast spectroscopic techniques, for example, ultrafast transient absorption (pump probe), time-resolved PL, (also streak camera, optical pump- THz probe, Kerr gating, four wave mixing etc.), provides valuable information with time resolution of fs-ps for various dynamic processes, extremely important for ultrafast carrier dynamic processes from dephasing to depopulation, usually for new materials/devices in new photovoltaic, photocatalytical, photonic, quantum information systems.  The generally most relevant processes include (carrier, exciton, phonon relaxation of phase and population), such as carrier-phonon scattering, cooling of hot electrons, exciton formation and dissociation, electron transfer etc.

Schematic and facility of ultrafast transient absorption

Ultrafast time-resolved PL (upconversion)

Examples of ultrafast transient absorption and time-resolved PL

References:
  • Yang et al. Acoustic-optical phonon up-conversion and hot-phonon bottleneck in lead-halide perovskites Nature Communications 8, 14120 (2017)
  • Wen et al. Intrinsic and Extrinsic Fluorescence in Carbon Nanodots: Ultrafast Time‐Resolved Fluorescence and Carrier Dynamics, Advanced Optical Materials 1 (2013), 173-178
  • Wen et al. Ultrafast Electron Transfer in Nanocomposite of Graphene Oxide-Au Nanocluster with Graphene Oxide As a Donor , Journal of Materials Chemistry C 2 (2014), 3826-3834
  • Xia et al. Hot carrier dynamics in HfN and ZrN measured by transient absorption spectroscopy, Solar Energy Materials and Solar Cells 150 (2016), 51-56

Fluorescence lifetime imaging microscopy (FLIM)

Combined TCSPC and confocal microscopy, FLIM can provide spatial distribution of PL intensity (photon number) and photon lifetime, with 200 nm spatial resolution and ps time resolution. With superior detection capability, such FLIM has detection sensitivity down to single molecule, single nanoparticle/quantum dot level – Single molecule spectroscopy.

(a) Facility for FLIM – TCSPC on a confocal microscope. (b)Typical FLIM image: brightness represents PL intensity/photon number and color represents photon lifetime.

(a) The PL decay from selected single point and area, (b) demonstrated electron transfer from singlet to triplet

References:

  • Zheng et al. Triggering the Passivation Effect of Potassium Doping in Mixed‐Cation Mixed‐Halide Perovskite by Light Illumination, Advanced Energy Materials, 1901016 (2019)
  • Deng et al. Dynamic study of the light soaking effect on perovskite solar cells by in-situ photoluminescence microscopy, Nano Energy 46 (2018), 356-364
  • Ma et al. Hole Transport Layer Free Inorganic CsPbIBr2 Perovskite Solar Cell by Dual Source Thermal Evaporation, Advanced Energy Materials 6 (2016), 1502202
  • Bu et al. Universal passivation strategy to slot-die printed SnO 2 for hysteresis-free efficient flexible perovskite solar module, Nature communications 9 (2018), 4609

Depth resolved FLIM (steady state and time-resolved PL)

Directly detecting the fluorescence and time-resolved PL can be achieved through two-photon excitation (combined with femtosecond pulses and confocal microscope). This is very useful non-destructive detection without dissecting or specifically fabricating layered sample. This technique can achieve depth resolved measurement, that is, not only on the surface but also under the surface, without dissecting.

(a) Depth resolved PL/TRPL by two-photon excitation. (b) tyical facility of Leica microsopy

(a) Depth-resolved PL spectra (b) one- and two-photon excited FLIM in perovskite

References:

  • Wenger et al. Consolidation of the optoelectronic properties of CH 3 NH 3 PbBr 3 perovskite single crystals, Nature communications 8 (2017), 590
  • Chen et al. Free charges versus excitons: photoluminescence investigation of InGaN/GaN multiple quantum well nanorods and their planar counterparts, Nanoscale 10 (2018), 5358-5365
  • Wen et al. Morphology and Carrier Extraction Study of Organic–Inorganic Metal Halide Perovskite by One- and Two-Photon Fluorescence Microscopy, J. Phys. Chem. Lett. 5 (2014) 3849
  • Chen et al. Tracking Dynamic Phase Segregation in Mixed‐Halide Perovskite Single Crystals under Two‐Photon Scanning Laser Illumination, Small Methods, 1900273