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A. Mishra
electrons. Recently, some ternary oxides, like Al-doped ZnO, Mg-doped ZnO, Lidoped ZnO, Ga-doped ZnO, In-doped ZnO) have also emerged as effective materials
for CIL (Shin et al. 2010; Yin et al. 2014; Soultati et al. 2019; Stubhan et al. 2013; Liao
et al. 2014). TiO 2 and ZnO, are the most widely used CILs in OSCs because of their
good transparency, environmentally stable, they can be solution-processed, nontoxic
and low cost. The WF of TiO x (−4.3 eV, LUMO ~4.4 eV) and ZnO (−4.3 eV, LUMO
~4.1 eV) are suitable for collecting electron and efficiently block hole. The low WF
of about 4.3 eV is suitable to modify the WF of both the ITO in inverted devices
or metal electrodes in conventional devices. The photovoltaic parameters of some
representative devices using various ETLs are summarized in Table 18.1.
The TiO X layer was prepared by sol-gel method from tetrabutyl titanate in isopropanol by spin-coating and efficiently used as CIL in inverted OSCs (Bao et al.
2014; Liu et al. 2012b). It has been found that the precursor and annealing temperature
strongly influence the optoelectronic properties of the TiO X layer. In conventional
device TiO X layer acts as optical spacer to enhance light absorption and also acts as
ETL/HBL. Kim et al. reported that by exchanging the isopropyl ligands of titanium
isopropoxide with 2-methoxyethanol formed an ETLs that need a shorter illumination time to fill shallow electron traps and improve the PCEs due to increase in both
J SC and V OC (Kim et al. 2013).
Lee et al. presented very stable OSC devices using sol-gel derived TiO X as ETL
in conventional device. Although the devices with and without TiO x generated very
similar PCEs ~4.0%, the air stability with TiO X layer was significantly enhanced by
two orders of magnitude (Lee et al. 2007). Park et al. reported PCEs of 6.1% for
PCDTBT:PC 71 BM based devices with internal quantum efficiency close to 100%
using TiO x as CIL (Park et al. 2009). Mor et al. demonstrated a PCE of 4.1%
in P3HT:PC 61 BM-based device using vertically aligned transparent TiO 2 nanotube
arrays. The pore size of the nanotube was tailored to infiltrate the polymer into the
nanotubes to form self-aligned aggregates. The devices displayed excellent external
quantum efficiency (EQE) up to 80% resulting from efficient charge separation at
both the P3HT-TiO 2 and P3HT-PC 61 BM interfaces (Mor et al. 2007). Sharma et al.
demonstrated an increased in the PCE from 2.8 to 4.1% by the introduction of TiO 2
layer between active layer (P3HT:fullerene free acceptor CSORG5) and Al metal
electrode in conventional device (Sharma et al. 2014).
The performance improvement of TiO X based solar cells generally required light
soaking to improve carrier densities, and reduce oxygen defect. The light soaking
significantly reduced the s-shape of J-V curve enhancing the FF from 0.26 to 0.60
and PCE from 1.3 to 3.3% (Lin et al. 2013). It has been shown that the n-doped TiO X
synthesized via controlling the nitrogen doping concentration in sol-gel synthesis
overcome the light-soaking process. N-doping significantly reduced the WF of TiO X
on the ITO (from 4.8 to 4.2 eV) and improved the Ohmic contact with the active
layer, thus increased the PCE from 2.13% (for undoped TiO X ) to 8.82% without light
soaking (Kim et al. 2015).
Yan et al. reported a light soaking free inverted solar cell by doping TiO 2 with
titanium oxide bis(2,4-pentanedionate) (TOPD). The treatment of TiO 2 /TOPD film
with UV light and then with ethanolamine eliminate the light soaking of the device
A. Mishra
electrons. Recently, some ternary oxides, like Al-doped ZnO, Mg-doped ZnO, Lidoped ZnO, Ga-doped ZnO, In-doped ZnO) have also emerged as effective materials
for CIL (Shin et al. 2010; Yin et al. 2014; Soultati et al. 2019; Stubhan et al. 2013; Liao
et al. 2014). TiO 2 and ZnO, are the most widely used CILs in OSCs because of their
good transparency, environmentally stable, they can be solution-processed, nontoxic
and low cost. The WF of TiO x (−4.3 eV, LUMO ~4.4 eV) and ZnO (−4.3 eV, LUMO
~4.1 eV) are suitable for collecting electron and efficiently block hole. The low WF
of about 4.3 eV is suitable to modify the WF of both the ITO in inverted devices
or metal electrodes in conventional devices. The photovoltaic parameters of some
representative devices using various ETLs are summarized in Table 18.1.
The TiO X layer was prepared by sol-gel method from tetrabutyl titanate in isopropanol by spin-coating and efficiently used as CIL in inverted OSCs (Bao et al.
2014; Liu et al. 2012b). It has been found that the precursor and annealing temperature
strongly influence the optoelectronic properties of the TiO X layer. In conventional
device TiO X layer acts as optical spacer to enhance light absorption and also acts as
ETL/HBL. Kim et al. reported that by exchanging the isopropyl ligands of titanium
isopropoxide with 2-methoxyethanol formed an ETLs that need a shorter illumination time to fill shallow electron traps and improve the PCEs due to increase in both
J SC and V OC (Kim et al. 2013).
Lee et al. presented very stable OSC devices using sol-gel derived TiO X as ETL
in conventional device. Although the devices with and without TiO x generated very
similar PCEs ~4.0%, the air stability with TiO X layer was significantly enhanced by
two orders of magnitude (Lee et al. 2007). Park et al. reported PCEs of 6.1% for
PCDTBT:PC 71 BM based devices with internal quantum efficiency close to 100%
using TiO x as CIL (Park et al. 2009). Mor et al. demonstrated a PCE of 4.1%
in P3HT:PC 61 BM-based device using vertically aligned transparent TiO 2 nanotube
arrays. The pore size of the nanotube was tailored to infiltrate the polymer into the
nanotubes to form self-aligned aggregates. The devices displayed excellent external
quantum efficiency (EQE) up to 80% resulting from efficient charge separation at
both the P3HT-TiO 2 and P3HT-PC 61 BM interfaces (Mor et al. 2007). Sharma et al.
demonstrated an increased in the PCE from 2.8 to 4.1% by the introduction of TiO 2
layer between active layer (P3HT:fullerene free acceptor CSORG5) and Al metal
electrode in conventional device (Sharma et al. 2014).
The performance improvement of TiO X based solar cells generally required light
soaking to improve carrier densities, and reduce oxygen defect. The light soaking
significantly reduced the s-shape of J-V curve enhancing the FF from 0.26 to 0.60
and PCE from 1.3 to 3.3% (Lin et al. 2013). It has been shown that the n-doped TiO X
synthesized via controlling the nitrogen doping concentration in sol-gel synthesis
overcome the light-soaking process. N-doping significantly reduced the WF of TiO X
on the ITO (from 4.8 to 4.2 eV) and improved the Ohmic contact with the active
layer, thus increased the PCE from 2.13% (for undoped TiO X ) to 8.82% without light
soaking (Kim et al. 2015).
Yan et al. reported a light soaking free inverted solar cell by doping TiO 2 with
titanium oxide bis(2,4-pentanedionate) (TOPD). The treatment of TiO 2 /TOPD film
with UV light and then with ethanolamine eliminate the light soaking of the device