18 Interfacial Materials for Organic Solar Cells
383
Using a low band gap polymer PCDTBT:PC 71 BM blend in combination with
low temperature sol-gel prepared ZnO as CIL and MoO x as HTL in an inverted
device reached PCEs up to 6.33%. (Sun et al. 2011) Liu et al. reported further PCE
improvement to 10.8 and 10.5% with high FF of 0.77 using PffBT4T-2OD:TC 71 BM
and PffBT4T-2OD:PC 71 BM blend and sol-gel processed ZnO prepared from diethyl
zinc as CIL (Liu et al. 2014). Yin et al. demonstrated that using sol-gel processed
ZnO by controlling the film thickness and MoO 3 as AIL PCE up to 5.05% could be
achieved with greater device stability compared to without ZnO. The V OC in these
devices was significantly enhanced from 0.22 V without ZnO to 1.04 V with ZnO
(Yin et al. 2013). The use of Cu 2 O, NiO and WO 3 as AIL showed comparatively lower
performance compared to MoO 3 which is ascribed to their energy levels differences,
and interfacial contacts with the active layer materials and metal anode. The starting
precursor materials also make a significant difference in the device performance.
MacLeod et al. revealed that using diethylzinc-derived ZnO as CIL a lower PCE
but more stable device could be obtained compared to the device derived from zinc
acetate precursor (MacLeod et al. 2015).
When a patterned ZnO prepared from sol-gel techniques was employed as CIL
in PTB7-Th:PC 71 BM based devices and MoO x /Al as top electrode the PCE could
be increased to 10.1% compared to 8.5% for the reference device without ZnO
(Chen et al. 2015). The improved performance was ascribed to collective effect
of the patterned-induced anti-reflection, light scattering, surface plasmon resonance,
reduced recombination probability and improved charge extraction at the ZnO:active
layer interface.
Using a combination of ZnO nanoparticles and TiO 2 nanorods an enhancement in
the PCE (8.82%) could be observed compared to bare ZnO nanoparticles (7.76%) and
TiO 2 nanorods (7.66%). This improvement was mainly due to interfacial contact and
reduced contact resistance and leakage current and facilitation of electron collection
and transport efficiency (Li et al. 2014b).
Trost et al. used solution-processed SnO x prepared from tetrakis(diethylamino)tin
as reactive precursor in isopropanol solution as electron extraction layer in inverted
OSC. The WF of SnO x was −4.1 eV similar to that of TiO x (−4.0 eV), thus generating
very similar PCE of around 3.0%. (Trost et al. 2012) However, the SnO x based devices
showed remarkable stability in contrast to TiO x at elevated temperature up to 80 °C in
air without encapsulation. Deposition of SnO X does not required any light soaking.
The deposition of a thin layer of SnO X (>20 nm) significantly change the WF from
4.8 eV of the ITO to the 4.2 eV of the SnO X -coated ITO which is attributed to the
formation of an interface dipole between ITO and SnO X . Using SnO X CILs prepared
by atomic layer deposition (ALD) at 80 °C without UV-treatment a high PCE of
5.9% could be achieved compared to 0.4% for OSCs based on TiO X and reduced the
s-shape for PCDTBT:PC 71 BM devices. The results demonstrated that SnO X acts as
barrier-free electron extraction layer without UV-irradiation and does not change its
WF (4.2 eV) upon illumination (Trost et al. 2015). However, a significant lowering
of WF from 4.4 to 3.9 eV was observed for TiO X after illumination.
Yang and co-workers revealed that the use of nanostructured gelled SnO 2 could
significantly enhanced the PCE of PBDTT-DPP:PC 61 BM-based device to 5.24%
383
Using a low band gap polymer PCDTBT:PC 71 BM blend in combination with
low temperature sol-gel prepared ZnO as CIL and MoO x as HTL in an inverted
device reached PCEs up to 6.33%. (Sun et al. 2011) Liu et al. reported further PCE
improvement to 10.8 and 10.5% with high FF of 0.77 using PffBT4T-2OD:TC 71 BM
and PffBT4T-2OD:PC 71 BM blend and sol-gel processed ZnO prepared from diethyl
zinc as CIL (Liu et al. 2014). Yin et al. demonstrated that using sol-gel processed
ZnO by controlling the film thickness and MoO 3 as AIL PCE up to 5.05% could be
achieved with greater device stability compared to without ZnO. The V OC in these
devices was significantly enhanced from 0.22 V without ZnO to 1.04 V with ZnO
(Yin et al. 2013). The use of Cu 2 O, NiO and WO 3 as AIL showed comparatively lower
performance compared to MoO 3 which is ascribed to their energy levels differences,
and interfacial contacts with the active layer materials and metal anode. The starting
precursor materials also make a significant difference in the device performance.
MacLeod et al. revealed that using diethylzinc-derived ZnO as CIL a lower PCE
but more stable device could be obtained compared to the device derived from zinc
acetate precursor (MacLeod et al. 2015).
When a patterned ZnO prepared from sol-gel techniques was employed as CIL
in PTB7-Th:PC 71 BM based devices and MoO x /Al as top electrode the PCE could
be increased to 10.1% compared to 8.5% for the reference device without ZnO
(Chen et al. 2015). The improved performance was ascribed to collective effect
of the patterned-induced anti-reflection, light scattering, surface plasmon resonance,
reduced recombination probability and improved charge extraction at the ZnO:active
layer interface.
Using a combination of ZnO nanoparticles and TiO 2 nanorods an enhancement in
the PCE (8.82%) could be observed compared to bare ZnO nanoparticles (7.76%) and
TiO 2 nanorods (7.66%). This improvement was mainly due to interfacial contact and
reduced contact resistance and leakage current and facilitation of electron collection
and transport efficiency (Li et al. 2014b).
Trost et al. used solution-processed SnO x prepared from tetrakis(diethylamino)tin
as reactive precursor in isopropanol solution as electron extraction layer in inverted
OSC. The WF of SnO x was −4.1 eV similar to that of TiO x (−4.0 eV), thus generating
very similar PCE of around 3.0%. (Trost et al. 2012) However, the SnO x based devices
showed remarkable stability in contrast to TiO x at elevated temperature up to 80 °C in
air without encapsulation. Deposition of SnO X does not required any light soaking.
The deposition of a thin layer of SnO X (>20 nm) significantly change the WF from
4.8 eV of the ITO to the 4.2 eV of the SnO X -coated ITO which is attributed to the
formation of an interface dipole between ITO and SnO X . Using SnO X CILs prepared
by atomic layer deposition (ALD) at 80 °C without UV-treatment a high PCE of
5.9% could be achieved compared to 0.4% for OSCs based on TiO X and reduced the
s-shape for PCDTBT:PC 71 BM devices. The results demonstrated that SnO X acts as
barrier-free electron extraction layer without UV-irradiation and does not change its
WF (4.2 eV) upon illumination (Trost et al. 2015). However, a significant lowering
of WF from 4.4 to 3.9 eV was observed for TiO X after illumination.
Yang and co-workers revealed that the use of nanostructured gelled SnO 2 could
significantly enhanced the PCE of PBDTT-DPP:PC 61 BM-based device to 5.24%