16 p-Type Dye Sensitized Solar Cells …
335
due to Co-substitution that increases the J SC value 0.50 mA/cm
2 , when using N719
and I
− /I 3
− as the sensitizer and the redox couple, respectively (Daniel et al. 2017).
Adèle Renaud et al. have successfully demonstrated the first DSC with p-type
LaOCuS nanoparticles as the photocathode. Transparent LaOCuS is an oxysulfide
material with similar VB potential to that of NiO, that enables effective hole injection
from the excited sensitizer. When using PMI-NDI as the sensitizer, it could attain
the following photovoltaic characteristics VOC = 150 mV, Jsc = 0.039 mA/cm
2 , ff
= 26%, η = 0.002% (Renaud et al. 2015).
An attractive discovery by Ze Yu et al. was based on finding p-type semiconducting
property in degenerate n-type semiconductors, could open a novel avenue for research
on p-DSCs. Indium tin oxide (ITO) is a n-type degenerate semiconductor having
good charge transport properties, and sufficient transparency. With the application
of ITO semiconductor in place of highly coloured NiO, and [Fe(acac) 3 ]
0/− redox
mediator, along with a new organic sensitizer, they have achieved a photo conversion
efficiency of 1.96 ± 0.12% (J SC = 5.65 mA cm
−2 , V OC = 700 mV). ITO owns a
significant local density of states below −4.8 eV, enabling transfer of electrons to
excited dye that produces a sustained photo cathodic current. A drawback of ITO is
faster recombination rate at the ITO–electrolyte interface. In order to overcome this
problem and attain higher efficiencies, the investigators have specifically designed
and synthesised an extended oligothiophene π-bridging sensitizer (PMI-8T-TPA).
Use of ITO as a blocking layer is another powerful modification that they have
implemented to achieve a V OC value of 758 mV in the presence of [Co(en) 3 ]
3+/2+ as
the electrolyte and 712 mV in the presence of [Fe(acac) 3 ]
0/− electrolyte (Yu et al.
2016).
Incorporation of porous metal–organic frameworks (MOFs) in fabrication of pDSCs is a novel approach by Junkuo Gao et al. They have reported a Ti(IV)-based
MOF, NTU-9, that shows p-type semiconductor behaviour with a bad gap of 1.72 eV.
It absorbs in the visible range up to 750 nm and has good photocatalytic activity.
Though there are numerous MOF applications related to n-DSCs, this is the first
novel MOF which has been developed with a potential as a semiconductor material
in p-DSCs. They also suggest that NTU-9 is a promising visible-light photocatalyst
for energy conversion and environmental remediation (Gao et al. 2014).
In addition to the Cu based delafossite materials, Shi et al. have successfully
introduced NiCo 2 S 4 nanosheet films obtained from NiCo 2 O 4 , to be applied as a
counter electrode in p-DSCs. Both NiCo 2 S 4 and NiCo 2 S 4 could be used to replace
Pt and NiO, respectively. Cost effectiveness is a major advantage. NiCo 2 S 4 is imbued
with high catalytic activity towards I
− /I 3
− electrolyte, generating an improved J SC
= 2.989 mA cm
−2 and η = 0.248% compared to when Pt is the counter electrode
(1.824 mA/cm
2 and 0.158%, respectively) but V OC is not improved (Shi et al. 2014).
Cuprous oxide (Cu 2 O) is an important semiconducting material due to its high
electron transmission. Studies on investigating electrodes made of pure Cu 2 O are
infrequent. Sisi et al. have demonstrated the possibility of applying Cu 2 O into pDSCs. They have compared commercial Cu 2 O particles and electrodes prepared
from Cu 2 O powder. In comparison, prepared Cu 2 O has shown better photovoltaic
performance than commercial Cu 2 O (J SC = 1.3 mA cm
−2 , V OC = 710 mV, FF =
335
due to Co-substitution that increases the J SC value 0.50 mA/cm
2 , when using N719
and I
− /I 3
− as the sensitizer and the redox couple, respectively (Daniel et al. 2017).
Adèle Renaud et al. have successfully demonstrated the first DSC with p-type
LaOCuS nanoparticles as the photocathode. Transparent LaOCuS is an oxysulfide
material with similar VB potential to that of NiO, that enables effective hole injection
from the excited sensitizer. When using PMI-NDI as the sensitizer, it could attain
the following photovoltaic characteristics VOC = 150 mV, Jsc = 0.039 mA/cm
2 , ff
= 26%, η = 0.002% (Renaud et al. 2015).
An attractive discovery by Ze Yu et al. was based on finding p-type semiconducting
property in degenerate n-type semiconductors, could open a novel avenue for research
on p-DSCs. Indium tin oxide (ITO) is a n-type degenerate semiconductor having
good charge transport properties, and sufficient transparency. With the application
of ITO semiconductor in place of highly coloured NiO, and [Fe(acac) 3 ]
0/− redox
mediator, along with a new organic sensitizer, they have achieved a photo conversion
efficiency of 1.96 ± 0.12% (J SC = 5.65 mA cm
−2 , V OC = 700 mV). ITO owns a
significant local density of states below −4.8 eV, enabling transfer of electrons to
excited dye that produces a sustained photo cathodic current. A drawback of ITO is
faster recombination rate at the ITO–electrolyte interface. In order to overcome this
problem and attain higher efficiencies, the investigators have specifically designed
and synthesised an extended oligothiophene π-bridging sensitizer (PMI-8T-TPA).
Use of ITO as a blocking layer is another powerful modification that they have
implemented to achieve a V OC value of 758 mV in the presence of [Co(en) 3 ]
3+/2+ as
the electrolyte and 712 mV in the presence of [Fe(acac) 3 ]
0/− electrolyte (Yu et al.
2016).
Incorporation of porous metal–organic frameworks (MOFs) in fabrication of pDSCs is a novel approach by Junkuo Gao et al. They have reported a Ti(IV)-based
MOF, NTU-9, that shows p-type semiconductor behaviour with a bad gap of 1.72 eV.
It absorbs in the visible range up to 750 nm and has good photocatalytic activity.
Though there are numerous MOF applications related to n-DSCs, this is the first
novel MOF which has been developed with a potential as a semiconductor material
in p-DSCs. They also suggest that NTU-9 is a promising visible-light photocatalyst
for energy conversion and environmental remediation (Gao et al. 2014).
In addition to the Cu based delafossite materials, Shi et al. have successfully
introduced NiCo 2 S 4 nanosheet films obtained from NiCo 2 O 4 , to be applied as a
counter electrode in p-DSCs. Both NiCo 2 S 4 and NiCo 2 S 4 could be used to replace
Pt and NiO, respectively. Cost effectiveness is a major advantage. NiCo 2 S 4 is imbued
with high catalytic activity towards I
− /I 3
− electrolyte, generating an improved J SC
= 2.989 mA cm
−2 and η = 0.248% compared to when Pt is the counter electrode
(1.824 mA/cm
2 and 0.158%, respectively) but V OC is not improved (Shi et al. 2014).
Cuprous oxide (Cu 2 O) is an important semiconducting material due to its high
electron transmission. Studies on investigating electrodes made of pure Cu 2 O are
infrequent. Sisi et al. have demonstrated the possibility of applying Cu 2 O into pDSCs. They have compared commercial Cu 2 O particles and electrodes prepared
from Cu 2 O powder. In comparison, prepared Cu 2 O has shown better photovoltaic
performance than commercial Cu 2 O (J SC = 1.3 mA cm
−2 , V OC = 710 mV, FF =