Environmental Engineering Reference
In-Depth Information
view of optical and electrical properties, provide various information of the
changes of electronic/chemical structure, energy level, and energy/charge transfer
at the interface.
All efforts on analyzing interface degradation mechanism and exploiting
characterization techniques are serving as pathways toward further optimization
and improvement of interface stability and device stability, such as essential
materials
used,
device
design
and
structure,
and
encapsulation,
significantly
crucial for the technological applications.
6.5.2 Outlook
If organic semiconducting and metallic materials and device design were further
developed, it is much promising that efficiencies of 10 would be obtained in a
relatively short term since 8 % efficiency has already been achieved by many
companies so far. The future of renewable and green OPV technology turns out to
be bright.
Another important factor is economical, i.e., to address the balance of product
cost, which demands the progress of technology such as new electrodes' alter-
native to current ITO and metals, cost-reduced synthesis process of photoactive
materials, low-cost encapsulation against oxygen and moisture diffusion, and
fabrication process of flexible cells and flexible integrated power supply.
The last requirement for commercial technology of OPVs is lifetime or
stability. High sensitivity to moisture, oxygen, UV light, and temperature results in
serious degradations of organic materials and entire devices. In order to diminish
the instability and extend the device lifetime, deep understanding and investigation
on degradation of each component and interface via chemical and physical ways
are
necessary,
followed
by
improvement
techniques.
Therefore,
study
of
degradation is suggested as follows:
6.5.2.1 Electrodes
ITO as highly conductive and transparent anode faces problems of lack of indium
reserves in nature and damage of indium to organic layer via diffusion. PE-
DOT:PSS as anode buffer layer exhibits slight acid property after adsorbing water,
leading to the etched ITO. Thus, an alternative to ITO is gallium doped ZnO
(GZO) which has a proper work function as anode and air stability. A replacement
of hydrophilic and acidic PEDOT:PSS with metal oxides is viable since metal
oxides with hole-transporting behavior as anode buffer layer exhibit appropriate
work functions and stability against air. However, most of metal oxides are grown
under high vacuum, which raises the process cost and hinders the large area.
Therefore, solution-processed metal oxides as buffer layers could provide many
opportunities and important insights on commercial OPVs.
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