402
A. Mishra
PCE of 6.3% was achieved with poly(thieno[3,4-b]thiophene-alt-benzodithiophene)
(PTB):PC 71 BM devices. The lowering of the ITO WF was originated from the
strong electrostatic self-assembled dipoles formed by the presence of protonated
amines within the ITO/PAA cathodes, forming a good Ohmic contact with LUMO
of PC 71 BM (Kang et al. 2012).
A ionic polyacetylene-based conjugated polymer electrolyte poly(N-dodecyl-2ethynylpyridiniumbromide) (PDEPB) was developed and used as interfacial dipole
layer to modify the ZnO surface and reduced its WF. Performance improvement was
observed for the ZnO/PDEPB modified interlayer due to lowering of interfacial resistance (probed by impedance spectroscopy measurement) and surface defects on ZnO
(Nam et al. 2017). PDEPB layer lowered the WF of the electron transporting ZnO
layer (by UPS measurement) and increased the built-in potential, hence enabling
efficient charge transport/extraction. The PCE was further improved to over 10%
using PTB7Th:PC 71 BM as photoactive layer and ZnO/PDEPB (0.5 mg/mL) interlayer (Nam et al. 2016). The increase in the V OC with PDEPB interlayers can be due
to the increased V bi caused by the dipolar interactions between PDEPB and ZnO,
basically contributing to accelerate the charge transport process.
Aryal et al. synthesized a series of polyacetylene-based pyridinium salts (PPy1PPy3) and used as cathode modifier of ZnO layer. Interfacial modification improved
the PCE from 7.46% for a ZnO-based control device to ~8.3% for PTB7:PC 71 BM
and to ~9.3% for PTB7-Th:PC 71 BM based devices (Aryal et al. 2018). Incorporation
of CIL suppressed the charge recombination and thus facilitated charge extraction.
The interlayer also protect the device from oxygen and humidity contamination and
improved the device stability (88% retention after ~1000 h).
After the successful use of non-conjugated polyelectrolytes PEI and PEIE as
neutral surface modifier by Kippelen and co-wokers, these materials have found
significant importance in the single junction and tandem photovoltaic device fabrications (Zhou et al. 2012a, b). These materials successfully tune the WFs of metal
electrodes, reduce the interfacial energy barrier and increase the build-in potential.
For example the WF of ITO can be reduced from ~4.4 to ~3.3 eV (measured by
UPS) by depositing thin film of solution-processed PEI or PEIE, originating from
the strong electrostatic self-assembled dipoles formed due to polar amine groups.
Heeger and Bazan group introduced 80% ethoxylated PEIE on the top of the
ZnO forming a composite film to enhance the device efficiency by lowering the
work function of ZnO (Kyaw et al. 2013). Inverted OSCs using a small molecule
p-DTS(FBTTh 2 ) 2 :PC 71 BM active layer demonstrated PCEs up to 7.88% using
ZnO/PEIE CIL which is higher compared to bare ZnO (6.29%) or PEIE (5.18%).
PEIE coating on ZnO lowered the WF of ZnO from 4.5 to 3.8 eV by creating a
dipole moment at the interface and thus supresses the trap-assisted recombination.
The increased V OC for ZnO/PEIE based devices (0.77 V) compared to bare ZnO
(0.72 V) can be attributed to the reduced WF of cathode after PEIE deposition.
Recently, Zhou and co-workers demonstrated that the PEIE interlayer can reduce
the performance of fullerene-free devices by reacting with the acceptor molecules
with amine leading to s-shaped J-V curve. The authors deactivate the chemical interaction by protonating the PEIE electrolyte processing from aqueous solution. OSCs
A. Mishra
PCE of 6.3% was achieved with poly(thieno[3,4-b]thiophene-alt-benzodithiophene)
(PTB):PC 71 BM devices. The lowering of the ITO WF was originated from the
strong electrostatic self-assembled dipoles formed by the presence of protonated
amines within the ITO/PAA cathodes, forming a good Ohmic contact with LUMO
of PC 71 BM (Kang et al. 2012).
A ionic polyacetylene-based conjugated polymer electrolyte poly(N-dodecyl-2ethynylpyridiniumbromide) (PDEPB) was developed and used as interfacial dipole
layer to modify the ZnO surface and reduced its WF. Performance improvement was
observed for the ZnO/PDEPB modified interlayer due to lowering of interfacial resistance (probed by impedance spectroscopy measurement) and surface defects on ZnO
(Nam et al. 2017). PDEPB layer lowered the WF of the electron transporting ZnO
layer (by UPS measurement) and increased the built-in potential, hence enabling
efficient charge transport/extraction. The PCE was further improved to over 10%
using PTB7Th:PC 71 BM as photoactive layer and ZnO/PDEPB (0.5 mg/mL) interlayer (Nam et al. 2016). The increase in the V OC with PDEPB interlayers can be due
to the increased V bi caused by the dipolar interactions between PDEPB and ZnO,
basically contributing to accelerate the charge transport process.
Aryal et al. synthesized a series of polyacetylene-based pyridinium salts (PPy1PPy3) and used as cathode modifier of ZnO layer. Interfacial modification improved
the PCE from 7.46% for a ZnO-based control device to ~8.3% for PTB7:PC 71 BM
and to ~9.3% for PTB7-Th:PC 71 BM based devices (Aryal et al. 2018). Incorporation
of CIL suppressed the charge recombination and thus facilitated charge extraction.
The interlayer also protect the device from oxygen and humidity contamination and
improved the device stability (88% retention after ~1000 h).
After the successful use of non-conjugated polyelectrolytes PEI and PEIE as
neutral surface modifier by Kippelen and co-wokers, these materials have found
significant importance in the single junction and tandem photovoltaic device fabrications (Zhou et al. 2012a, b). These materials successfully tune the WFs of metal
electrodes, reduce the interfacial energy barrier and increase the build-in potential.
For example the WF of ITO can be reduced from ~4.4 to ~3.3 eV (measured by
UPS) by depositing thin film of solution-processed PEI or PEIE, originating from
the strong electrostatic self-assembled dipoles formed due to polar amine groups.
Heeger and Bazan group introduced 80% ethoxylated PEIE on the top of the
ZnO forming a composite film to enhance the device efficiency by lowering the
work function of ZnO (Kyaw et al. 2013). Inverted OSCs using a small molecule
p-DTS(FBTTh 2 ) 2 :PC 71 BM active layer demonstrated PCEs up to 7.88% using
ZnO/PEIE CIL which is higher compared to bare ZnO (6.29%) or PEIE (5.18%).
PEIE coating on ZnO lowered the WF of ZnO from 4.5 to 3.8 eV by creating a
dipole moment at the interface and thus supresses the trap-assisted recombination.
The increased V OC for ZnO/PEIE based devices (0.77 V) compared to bare ZnO
(0.72 V) can be attributed to the reduced WF of cathode after PEIE deposition.
Recently, Zhou and co-workers demonstrated that the PEIE interlayer can reduce
the performance of fullerene-free devices by reacting with the acceptor molecules
with amine leading to s-shaped J-V curve. The authors deactivate the chemical interaction by protonating the PEIE electrolyte processing from aqueous solution. OSCs