[Sample B: Approval/Signature Sheet]

carrier mobility and absorption in the visible and new-infrared spectral regions, in
combination with a high interfacial gap energy at the donor-acceptor interface [8].
Among these, 2,4-bis [4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine (SQ)
dyes with four hydroxyl groups at the 2,6-positions of the two phenyl rings with four
hydroxyl groups [14] have been identified as donors that absorb at wavelengths >650
nm while, when combined with a C 60 acceptor layer, have a larger open circuit voltage
(V oc ) than that of the commonly used copper phthalocyanine (CuPc)/C 60 cell [15].
2.2 Cell series resistance
The series resistance (R s ) of an organic solar cell reduces its power conversion
efficiency (η p ). The series resistance comes from the finite electrical conductivities of the
organic materials and contact electrodes. For an (R s =0) ideal PV cell, the short-circuit
current densities (J sc ) depends linearly on the incident power density (P o ), the opencircuit
voltage (V oc ) increases logarithmically with P o , and the Fill Factor (FF) also
increases with P o . For this case, the efficiency, is:
P
p
P
J V FF
P
m sc oc
0 0
(2.1)
organic solar cells have resistance R s ≠0, limits by the low carrier mobility and electrical
conductivity of organic materials. To obtain high J sc and FF, solar cells must have low R s .
In organic solar cells, the FF is limited by the carrier drift length, L d , [15]
Ld
E
(2.2)
where is the carrier mobility, τ is the carrier recombination lifetime and E is the electric
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