Environmental Engineering Reference
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(a)
O
O
O
O
PC
61
BM
PC
71
BM
(b)
O
S
N
N
N
S
S
n
S
n
n
O
MEH-PPV
P3HT
PCDTBT
O
S
S
N
N
N
N
Si
n
O
S
S
S
S
n
n
MDMO-PPV
PSBTBT
PCPDTBT
Scheme 3.1 Chemical structures of the most widely used (a) acceptors (PC
61
BM and PC
71
BM)
and (b) donors (P3HT, PCDTBT, MEH-PPV, MDMO-PPV, PCPDTBT, and PSBTBT)
interface can inevitably break the p-conjugated system of organic layer, and
thereby lead to poor stability of Al cathode [
19
,
20
]. Hence, various interfacial
materials were inserted into the organic active layer/Al junction to improve the
interface contact properties and thereby photovoltaic performance of BHJ-PSCs.
The summary of performance of conventional PSCs using different cathode
interlayer designs are listed in Table
3.1
and the chemical structures of organic
materials
used
as
cathode
interlayer
in
conventional
PSCs
are
shown
in
Scheme
3.2
.
3.2.1.1 Metal and Inorganic Compounds as Cathode Interlayer
Low work-function metals, such as calcium (Ca) or barium (Ba), which were two
widely used interfacial materials for polymeric light-emitting diodes (PLEDs)
[
21
,
22
], were also usually inserted into the interface between Al and organic
active layer to further improve the device performance via the formation of ideal
Ohmic contact at interface. The BHJ-PSCs with a thin layer of Ca or Ba between
Al and organic active layer usually exhibited superior device performance, espe-
cially open circuit voltage (V
oc
) with respect to PSCs with bare Al as cathode.
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