18 Interfacial Materials for Organic Solar Cells
385
terephthalate)/indium tin oxide substrates were also prepared showing PCE of 8.93%
(Liu et al. 2016a). The conductivity of AZO was enhanced by three order of magnitude compared to neat ZnO, therefore a thicker film can be prepared with AZO
(above 100 nm) (Stubhan et al. 2011). Similar enhancement in conductivity was also
observed for Ga-doped ZnO and In-doped ZnO thus enabling thicker film formation
up to 200 nm. (Shin et al. 2010; Puetz et al. 2011) The device performance was
improved after doping due to improved electron transport/hole blocking properties.
Liao et al. present a high efficiency and stable inverted OSCs using sol-gel processed In–doped ZnO as CIL. The PTB7-Th:PC 71 BM device exhibited a PCE of
9.11% compared to 8.25% for undoped ZnO (Liao et al. 2014). The LUMO energy
level lowered from 4.29 to 4.62 eV upon doping. In-doping also improved the electron
mobility from 8.25 × 10
−5 to 9.5 × 10
−3 cm
2 V
−1 s
−1 and enhanced the conductivity
from 0.015 to 8.51 S cm
−1 .
Gadisa et al. prepared AZO nanoparticle stabilized with a TiO X complex. The
P3HT:PC 61 BM device prepared with modified CIL and WO 3 as AIL generated high
FF of 0.68 due to efficient hole blocking property of AZO-Ti and could solve the issue
related to interfacial recombination in the devices (Gadisa et al. 2013). Brabec and
co-workers improved the device performance of P3HT:PC 61 BM device by employing a C 60 self-assembled monolayer (SAM) containing phosphonic acid anchoring
group (Stubhan et al. 2012). The series resistance in the device was reduced keeping the shunt resistance high. The use of ZnO-poly(vinyl pyrrolidone) (PVP) based
composite films prepared using sol-gel method as ETL, demonstrated PCEs >8%
under AM 1.5G illumination at 100 mW cm
−2 (Small et al. 2012). ZnO/ionic liquid
composite interlayer was also fabricated as CIL and show improved photovoltaic performance over 9%. The ionic nature of [BMIM]BF 4 form interfacial dipole between
active layer and ZnO and facilitate charge transport. (Yu et al. 2015) Electrochemical
impedance spectral analysis showed the reduction of charge transfer resistance from
ZnO to ZnO/[BMIM]BF 4 .
It has been realized that the binary and ternary metal oxides as well their doped
state whenever required can be used as efficient CILs in BHJ solar cells. Most importantly, the low temperature processing methods using sol-gel approach is viable to
apply in other electronic devices including flexible substrate.
18.2.1.2 Organic Molecules as CIL
In this section we will summarize the current development on the use of some selective organic molecules as CIL and discuss their molecular design and implementation in OSCs. In order to improve the device performance along with new donor and
acceptor material design, it is important to get control over the interfacial properties.
Toward this goal, many new organic interfacial material systems are being designed
and synthesized to optimize the energy levels of electrodes in order to increase the
device performance. Earlier, BCP has been extensively used as an efficient EBL in
vacuum-processed devices (Peumans and Forrest 2001).
385
terephthalate)/indium tin oxide substrates were also prepared showing PCE of 8.93%
(Liu et al. 2016a). The conductivity of AZO was enhanced by three order of magnitude compared to neat ZnO, therefore a thicker film can be prepared with AZO
(above 100 nm) (Stubhan et al. 2011). Similar enhancement in conductivity was also
observed for Ga-doped ZnO and In-doped ZnO thus enabling thicker film formation
up to 200 nm. (Shin et al. 2010; Puetz et al. 2011) The device performance was
improved after doping due to improved electron transport/hole blocking properties.
Liao et al. present a high efficiency and stable inverted OSCs using sol-gel processed In–doped ZnO as CIL. The PTB7-Th:PC 71 BM device exhibited a PCE of
9.11% compared to 8.25% for undoped ZnO (Liao et al. 2014). The LUMO energy
level lowered from 4.29 to 4.62 eV upon doping. In-doping also improved the electron
mobility from 8.25 × 10
−5 to 9.5 × 10
−3 cm
2 V
−1 s
−1 and enhanced the conductivity
from 0.015 to 8.51 S cm
−1 .
Gadisa et al. prepared AZO nanoparticle stabilized with a TiO X complex. The
P3HT:PC 61 BM device prepared with modified CIL and WO 3 as AIL generated high
FF of 0.68 due to efficient hole blocking property of AZO-Ti and could solve the issue
related to interfacial recombination in the devices (Gadisa et al. 2013). Brabec and
co-workers improved the device performance of P3HT:PC 61 BM device by employing a C 60 self-assembled monolayer (SAM) containing phosphonic acid anchoring
group (Stubhan et al. 2012). The series resistance in the device was reduced keeping the shunt resistance high. The use of ZnO-poly(vinyl pyrrolidone) (PVP) based
composite films prepared using sol-gel method as ETL, demonstrated PCEs >8%
under AM 1.5G illumination at 100 mW cm
−2 (Small et al. 2012). ZnO/ionic liquid
composite interlayer was also fabricated as CIL and show improved photovoltaic performance over 9%. The ionic nature of [BMIM]BF 4 form interfacial dipole between
active layer and ZnO and facilitate charge transport. (Yu et al. 2015) Electrochemical
impedance spectral analysis showed the reduction of charge transfer resistance from
ZnO to ZnO/[BMIM]BF 4 .
It has been realized that the binary and ternary metal oxides as well their doped
state whenever required can be used as efficient CILs in BHJ solar cells. Most importantly, the low temperature processing methods using sol-gel approach is viable to
apply in other electronic devices including flexible substrate.
18.2.1.2 Organic Molecules as CIL
In this section we will summarize the current development on the use of some selective organic molecules as CIL and discuss their molecular design and implementation in OSCs. In order to improve the device performance along with new donor and
acceptor material design, it is important to get control over the interfacial properties.
Toward this goal, many new organic interfacial material systems are being designed
and synthesized to optimize the energy levels of electrodes in order to increase the
device performance. Earlier, BCP has been extensively used as an efficient EBL in
vacuum-processed devices (Peumans and Forrest 2001).