[Sample B: Approval/Signature Sheet]

materials; and (2) create continuous pathways for charge transport to the respective
electrodes [16]. Usually, the simple bilayer planar HJ is vacuum deposited using smallmolecular-
weight organic donor and acceptor materials, although the organic layer
thickness and cell efficiency are limited by their short L D . Compared with polymer
materials, it is more difficult for small-molecular-weight materials to achieve a bulk HJ,
since their phase separation usually occurs in the solid rather than in the liquid phase.
Simply mixing materials by co-evaporation of the donor and acceptor materials can result
in a significant decrease in charge carrier mobility, as has been observed by the codeposition
of D/A pair, copper phthalocyanine (CuPc)/PTCBI and CuPc/C 60 [22]. When
deposited into a mixture, their crystal stacks are disrupted, introducing charge trapping
and scattering during transport to the electrode. Hence, mixed-layer devices typically
have high series resistance, resulting in carrier recombination. One means to circumvent
the low mobility of charge in disordered organic films is to create morphological order
that leads to a low resistance to charge conduction, lacking bottlenecks or islands that
impede carrier extraction through organic vapor phase deposition (OVPD) [7]. The
control of organic film crystallization and morphology results in a low resistance, ordered
and interdigitated interface in a bulk CuPc:C 60 HJ cell. This significantly improves
efficiency over otherwise a planar CuPc/C 60 HJ cell.
1.3 Characteristics of organic solar cells
Due to the potential for low cost solar energy conversion, OPVs have attracted
tremendous attention since a 0.95 % power conversion efficiency solar cell based on a
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