11 The Confinement and Migration of Charge-Carriers in Lead …
207
Fig. 11.8 PL decay profiles
of a PNC film excited with
low-intensity laser
(0.0175 µJ/pulse) (red)
before and (blue) after
doping with C 60 .
Reproduced with permission
from Ref. [35]. Copyright
2019, Royal Society of
Chemistry
unexpectedly delayed PL. On the other hand, the diffusion of photogenerated chargecarriers is spatially confined by increasing the intensity of excitation laser, which is
the result of an increase in the carrier concentration. Accordingly, the rate of radiative recombination within the irradiated area controls over the diffusion, providing
amplified emission.
The degree of charge-carrier migration across PNCs in their close-packed
assembly (or film) depends upon their packing density [34]. As seen in Fig. 11.7c,
the PL spectra of a loose-packed PNC film is blue-shifted, whereas that of a closepacked film is red-shifted. Additionally, as shown in Fig. 11.7c and d, a red-shifted
PL spectrum is associated with long PL lifetime. The low-energy photons which
are associated with the delayed emission in PNC film point toward the diffusion
of charge-carriers through closely-spaced energy states during which some energy
is lost, resulting in long-lived low-energy photons. Such delayed PL, as a result of
long-range migration of photogenerated charge-carriers, in close-packed assembly of
PNCs is a promising property for the harvesting of charge-carriers in high-efficiency
solar cells. Indeed, an appreciable rate of electron transfer (3.3 × 10
6 s
−1 ) is achieved
from the photoexcited close-packed assembly of PNCs to fullerene (C 60 ), revealed
by the fast PL decay of the PNC film doped with C 60 , when compared to a pristine
film without C 60 , as shown in Fig. 11.8 [35].
11.5 Conclusions
The optical and electronic properties of individual QDs modify when they are
arranged into superlattices. The overlapping of QDs electronic wavefunctions in
the lattice facilitates the long-range diffusion or hopping of excitons. Due to the high
exciton binding energy in strongly quantum-confined systems, the diffusing excitons
207
Fig. 11.8 PL decay profiles
of a PNC film excited with
low-intensity laser
(0.0175 µJ/pulse) (red)
before and (blue) after
doping with C 60 .
Reproduced with permission
from Ref. [35]. Copyright
2019, Royal Society of
Chemistry
unexpectedly delayed PL. On the other hand, the diffusion of photogenerated chargecarriers is spatially confined by increasing the intensity of excitation laser, which is
the result of an increase in the carrier concentration. Accordingly, the rate of radiative recombination within the irradiated area controls over the diffusion, providing
amplified emission.
The degree of charge-carrier migration across PNCs in their close-packed
assembly (or film) depends upon their packing density [34]. As seen in Fig. 11.7c,
the PL spectra of a loose-packed PNC film is blue-shifted, whereas that of a closepacked film is red-shifted. Additionally, as shown in Fig. 11.7c and d, a red-shifted
PL spectrum is associated with long PL lifetime. The low-energy photons which
are associated with the delayed emission in PNC film point toward the diffusion
of charge-carriers through closely-spaced energy states during which some energy
is lost, resulting in long-lived low-energy photons. Such delayed PL, as a result of
long-range migration of photogenerated charge-carriers, in close-packed assembly of
PNCs is a promising property for the harvesting of charge-carriers in high-efficiency
solar cells. Indeed, an appreciable rate of electron transfer (3.3 × 10
6 s
−1 ) is achieved
from the photoexcited close-packed assembly of PNCs to fullerene (C 60 ), revealed
by the fast PL decay of the PNC film doped with C 60 , when compared to a pristine
film without C 60 , as shown in Fig. 11.8 [35].
11.5 Conclusions
The optical and electronic properties of individual QDs modify when they are
arranged into superlattices. The overlapping of QDs electronic wavefunctions in
the lattice facilitates the long-range diffusion or hopping of excitons. Due to the high
exciton binding energy in strongly quantum-confined systems, the diffusing excitons