18 Interfacial Materials for Organic Solar Cells
407
into ZnO ETL, the stability of ETL increased and is related to the suppressed aggregations of ZnO nanoparticles.
Mishra et al. demonstrated a low energy loss (E loss ) in conventional fullerene-free
solar cells using P1:DCI-2 blend and PFN as CIL. The device exhibited a PCE of
6.94% with low E loss of 0.39 V showing the importance of PFN layer on device
performance (Mishra et al. 2017). The authors further reported a PCE of 7.24%
using a D: A based organic molecule TPA-SN5-DCV:PC 71 BM blend using PFN/Al
cathode after solvent additive treatment followed by thermal annealing (Mishra et al.
2018).
Duan et al. developed a conjugated alcohol soluble PCDTBT-N functionalized
with tertiaryamine pendant groups and used as buffer layer in metal: organic interface
to improve electron collection efficiency (Duan et al. 2013a). The amino groups
formed complex with C 70 and act as hole traps as well shift the Fermi level from
about 4.6–4.2 eV. PCDTBT:PC 71 BM-based devices gave PCE of 5.32% compared
to without interlayer due to the reduced transport loss for efficient electron collection
through the n-doping of PC 71 BM.
Kim et al. prepared a conjugated polyelectrolyte PBN consisting of benzodithiophene and fluorine units as CIL for ZnO surface modification (Kim et al. 2014). PBN
creates an interfacial dipoles at the ZnO/organic interface and improve the contact
between the layers thus enhanced the PCE of PTB7:PC 71 BM by about 21% i.e. from
7.1 to 8.6%.
Hou group developed a unique polymer poly[9,9-bis(1-sulfopropane-3-yl)fluorene-2,7-diyl-alt-(2,2
-bithiophene-5,5
)-diyl] (PFS) comprising sulfonic acid
containing fluorene and bithiophene unit which acts as both anode and cathode interfacial layers. The device with PDBT-TS1:PC 71 BM achieved a high PCE of 9.48%
and comparable to device with PEDOT:PSS (9.76%) or Mg (9.63%) as anode and
cathode interlayers (Xu et al. 2016).
Sun et al. reported fullerene-free OSCs with a PCE of over 11% by introducing
n-type PFN or PFN-2TNDI as CIL (Sun et al. 2017). The results revealed that the
contact between the n-type interlayer and the donor provides an extra interface for
charge dissociation and the matching of energy levels between the interlayer and
the acceptor allows efficient electron extraction from the BHJ at the interface. Furthermore, in contrast to PFN, PFN-2TNDI layer is suitable for exciton dissociation
due to appropriate energy level offset between the donor and interlayer resulting in
enhanced photocurrent generation.
A conjugated polymer PT 2 NDISB containing napthalenediimide and bithiophene
with pendant zwitterionic groups was synthesized via Suzuki coupling reaction and
incorporated as interlayer between active layer and Ag in OSCs. A thin layer of
polymer interlayer (~8 nm) increased the device efficiency from 3.17 to 10.19%.
The interlayer lowered the WF to 3.8 eV, increase the V bi and reduces the pinholes
formation. The CIL act as optical spacers to enhance total photocurrent generated
within the active layer (Liu et al. 2015b). Using a NDI derivative PNDIT10 N as CIL
and MoO x as AIL, the inverted device using PTB7-Th:PC 71 BM gave a PCE of 7.0%
(Bjuggren et al. 2018). UPS spectroscopy demonstrated reduction in the ITO work
function after surface modification which is related to the formation of interfacial
407
into ZnO ETL, the stability of ETL increased and is related to the suppressed aggregations of ZnO nanoparticles.
Mishra et al. demonstrated a low energy loss (E loss ) in conventional fullerene-free
solar cells using P1:DCI-2 blend and PFN as CIL. The device exhibited a PCE of
6.94% with low E loss of 0.39 V showing the importance of PFN layer on device
performance (Mishra et al. 2017). The authors further reported a PCE of 7.24%
using a D: A based organic molecule TPA-SN5-DCV:PC 71 BM blend using PFN/Al
cathode after solvent additive treatment followed by thermal annealing (Mishra et al.
2018).
Duan et al. developed a conjugated alcohol soluble PCDTBT-N functionalized
with tertiaryamine pendant groups and used as buffer layer in metal: organic interface
to improve electron collection efficiency (Duan et al. 2013a). The amino groups
formed complex with C 70 and act as hole traps as well shift the Fermi level from
about 4.6–4.2 eV. PCDTBT:PC 71 BM-based devices gave PCE of 5.32% compared
to without interlayer due to the reduced transport loss for efficient electron collection
through the n-doping of PC 71 BM.
Kim et al. prepared a conjugated polyelectrolyte PBN consisting of benzodithiophene and fluorine units as CIL for ZnO surface modification (Kim et al. 2014). PBN
creates an interfacial dipoles at the ZnO/organic interface and improve the contact
between the layers thus enhanced the PCE of PTB7:PC 71 BM by about 21% i.e. from
7.1 to 8.6%.
Hou group developed a unique polymer poly[9,9-bis(1-sulfopropane-3-yl)fluorene-2,7-diyl-alt-(2,2
-bithiophene-5,5
)-diyl] (PFS) comprising sulfonic acid
containing fluorene and bithiophene unit which acts as both anode and cathode interfacial layers. The device with PDBT-TS1:PC 71 BM achieved a high PCE of 9.48%
and comparable to device with PEDOT:PSS (9.76%) or Mg (9.63%) as anode and
cathode interlayers (Xu et al. 2016).
Sun et al. reported fullerene-free OSCs with a PCE of over 11% by introducing
n-type PFN or PFN-2TNDI as CIL (Sun et al. 2017). The results revealed that the
contact between the n-type interlayer and the donor provides an extra interface for
charge dissociation and the matching of energy levels between the interlayer and
the acceptor allows efficient electron extraction from the BHJ at the interface. Furthermore, in contrast to PFN, PFN-2TNDI layer is suitable for exciton dissociation
due to appropriate energy level offset between the donor and interlayer resulting in
enhanced photocurrent generation.
A conjugated polymer PT 2 NDISB containing napthalenediimide and bithiophene
with pendant zwitterionic groups was synthesized via Suzuki coupling reaction and
incorporated as interlayer between active layer and Ag in OSCs. A thin layer of
polymer interlayer (~8 nm) increased the device efficiency from 3.17 to 10.19%.
The interlayer lowered the WF to 3.8 eV, increase the V bi and reduces the pinholes
formation. The CIL act as optical spacers to enhance total photocurrent generated
within the active layer (Liu et al. 2015b). Using a NDI derivative PNDIT10 N as CIL
and MoO x as AIL, the inverted device using PTB7-Th:PC 71 BM gave a PCE of 7.0%
(Bjuggren et al. 2018). UPS spectroscopy demonstrated reduction in the ITO work
function after surface modification which is related to the formation of interfacial