1. Study of Small-Molecule Thin Organic Films Deposited on Porous Silicon Substrates
Zbigniew Łukasiak Andrzej Korcala, Przemysław Płóciennik, Anna Zawadzka
Department of Technical and Applied Physics
Faculty of Physics, Astronomy and Informatics
Nicolaus Copernicus University - Toruń

2. Outline Introduction Sample preparation
Porous silicon (PSi)
copper phthalocyanine – by PVD
Characterisation by time resolved spectroscopy
Results for PSi and PSi/CuPc
Summary
Study of Small-Molecule Thin Organic Films Deposited on Porous Silicon Substrates

3. Why porous silicon is interesting?
Science: Porous Si is silicon structure and bulk Si is inefficient at emitting light, even at cryogenic temperatures.
Economy: Simple technology and low costs.
Technology: Silicon is the most technologically important material, dominating the microelectronics revolution that influences our everyday lives.
Study of Small-Molecule Thin Organic Films Deposited on Porous Silicon Substrates

4. Porous silicon Si mixture of nanostructures
A - silicon wafer (substrate) B - wires (>500 nm)
C - quantum wires (1-100 nm) D , G - nanocrystallites (1-10 nm)
E - oxide layer F - contact layer
surface to volume ratio m2/cm3
Study of Small-Molecule Thin Organic Films Deposited on Porous Silicon Substrates

5. Preparation of porous silicon
Study of Small-Molecule Thin Organic Films Deposited on Porous Silicon Substrates

6. Copper phthalocyanine (CuPc)
small-molecule organic material used as a hole transport layer in OLED and OPV structures
Study of Small-Molecule Thin Organic Films Deposited on Porous Silicon Substrates

7. Thin films preparation by PVD (thermal evaporation in vacuum)
Study of Small-Molecule Thin Organic Films Deposited on Porous Silicon Substrates

8. Characterisation by time resolved photoluminescence
for nitrogen laser
sample
~200 s - for porous silicon
~5 ns PM
transient recorder S
photomultiplier
Boxcar, digital oscilloscope, RTMS
Filter (monochromator) L
Pulse Laser
Study of Small-Molecule Thin Organic Films Deposited on Porous Silicon Substrates

9. Time resolved spectra & decay curves
INTENSITY
OBSERVATION WAVELENGTH
constant wavelength, changed delay
decay curves of luminescence
constant delay, changed wavelength
luminescence time resolved spectra
TIME
Study of Small-Molecule Thin Organic Films Deposited on Porous Silicon Substrates

10. Photoluminescence time-resolved spectra for different delays
0, 5μs, 10μs, 20μs, 40μs, 60μs, 80μs, 100μs,150μs
Study of Small-Molecule Thin Organic Films Deposited on Porous Silicon Substrates

11. Photoluminescence (decomposed as a sum of few Gaussians)
Study of Small-Molecule Thin Organic Films Deposited on Porous Silicon Substrates

12. Decay of photoluminescence
Study of Small-Molecule Thin Organic Films Deposited on Porous Silicon Substrates

13. Recombination radiative (slow decay) defect tunnelling nonradiative
(fast decay)
radiative
(slow decay)
Study of Small-Molecule Thin Organic Films Deposited on Porous Silicon Substrates

14. Conclusions
PL spectra of PSi/CuPc exhibit the same multiband structure like for fresh prepared PSi.
The results shows that origin of PL is the same for fresh and organic coated samples.
The organic material penetrates deep into PSi skeleton and influences generation and recombination processes of carriers in PSi structure.
The results are interesting for aplication of PSi as a part of hybrid PSi-organic photovoltaic devices or selective gas detectors (“electrical noses”)
Study of Small-Molecule Thin Organic Films Deposited on Porous Silicon Substrates

15. Thank you for your attention
Study of Small-Molecule Thin Organic Films Deposited on Porous Silicon Substrates

16. Study of Small-Molecule Thin Organic Films Deposited on Porous Silicon Substrates

17. Study of Small-Molecule Thin Organic Films Deposited on Porous Silicon Substrates

18. Relaxation of carriers in PSi structure
Wr - radiative recombination (slow)
Wnr - nonradiative recombination (fast)
Wij - migration between different zones of structure (very slow)
„loses”
delayed injection
Study of Small-Molecule Thin Organic Films Deposited on Porous Silicon Substrates

19. Model of luminescence
Study of Small-Molecule Thin Organic Films Deposited on Porous Silicon Substrates

20. Future NOT ONLY LEDs flat displays solar cells gas sensors
humidity sensors
„electronic noses”
enviroment monitoring
blood diagnostics
implants - „cyberbones”
explosives !
Study of Small-Molecule Thin Organic Films Deposited on Porous Silicon Substrates