knjiga solarna energija dobra

670 DYE-SENSITIZED SOLAR CELLS
15.1.2.6 Sealing materials
A sealing material is needed to prevent the leakage of the electrolyte and the evaporation
of the solvent. Chemical and photochemical stability of the sealing material against the
electrolyte component, iodine, and the solvent is required. Surlyn (Du Pont), a copolymer
of ethylene and acrylic acid, meets these requirements.
15.1.3 Mechanism
This section describes the primary processes that occur in a DSSC and discusses the solar
energy–to–current conversion efficiencies of cells.
15.1.3.1 Primary processes
Figure 15.6 is a schematic energy diagram of a DSSC. The following primary steps
convert photons to current:
1. Ru complex photosensitizers adsorbed on the TiO 2 surface absorb incident photon flux.
2. The photosensitizers are excited from the ground state (S) to the excited state (S ∗ )
owing to the MLCT transition. The excited electrons are injected into the conduction
band of the TiO 2 electrode, resulting in the oxidation of the photosensitizer.
S + hν → S ∗ [1]
S ∗ → S + + e − (TiO 2 ) [2]
Electrons
Energy level
E/V vs NHE
Load
Counter
electrode (Pt)
−0.5
E c (−0.5 V)
Injection
Dye LUMO
(−0.7 V)
Fermi level
0
Light
TiO 2
photoelectrode
∆E 1
∆E 2
Excitation
E g
Max.
voltage
0.5
1.0
HOMO
(1.0 V)
I − /I 3
− redox
mediator
(0.4 V)
Electrolyte
Glass TCO
TCO Glass
Figure 15.6
Schematic energy diagram and operating principle of DSSC