334
S. Peiris et al.
on CuGaO 2 plates conducted by Zhen Xu et al. produced devices with a remarkably
high J SC = 2.05 mA cm
−2 incorporating I
− /I 3
− electrolyte as the redox mediator.
Nanoplates of 100–200 nm diameter and thickness of 20–30 nm were obtained, and
optimization of temperature for the hydrothermal synthesis was done (Xu et al. 2014).
Adèle Renaud et al. have done further modification to CuGaO 2 based p-DSCs by
doping Mg with assembly of PMI-NDI dyad as the dye, and tris(4,4
-bis-tert-butyl2,2
-bipyridine)cobalt(II/III) as the electrolyte. They found out that there is a 73%
increase in photovoltaic yield compared to undoped CuGaO 2 , when doped with 1%
of Mg. But this performance is lost when the doping is increased above 1% of Mg
(V OC = 305 mV; J SC = 0.415 mA cm
−2 ; FF = 0.35; η = 0.45) (Renaud et al. 2013a).
CuAlO 2 is another type of delafossite which was synthesised by Ahmed and
coworkers under controlled oxygen pressure (pO 2 ) of 105 atm and at a temperature
of 775
° C. A uniform particle size of 35 nm was obtained and cathodic photocurrent
with J SC = 0.954 mA cm
−2 under 1.5 sun illumination (Ahmed et al. 2014). Miclau
et al. have conducted a study based on the effect of polymorphism on photovoltaic
performance of CuAlO 2 delafossite nanomaterials by synthesizing nanocrystalline
3R or mixture of 2H and 3R polytypes. Key factors that cause the formation of poly
types are temperature and autogenous pressure. Even a small concentration of 2H
polytype caused raise energy conversion efficiency by 49% compared to pure 3RCuAlO 2 polytype. The reason for higher efficiencies may be because of the presence
of smaller Cu-Cu distance of 2H polytype compared to that of 3R polytype. As the
electrical conductivity predominantly occurs through the Cu
+ plane, 2H polytype
generates a higher photocurrent density (J SC ) (Miclau et al. 2017).
The first application of hydrothermally synthesised, Mg doped CuCrO 2 delafossite
material in p-DSCs was reported by Xiong et al. They have observed an enhancement
in optical transmittance and reduction of crystallite size, that leads to improvement
of J SC by approximately 27%, when CuCrO 2 was doped with Mg. Lower valence
band edge and faster hole diffusion coefficient has been observed in CuCr 0.9 Mg 0.1 O 2
(in comparison to NiO), producing a V OC of 201 mV and J SC of 1.51 mA cm
−2 . The
efficiency obtained was 0.132% which is nearly three times higher compared to NiObased reference devices with a V OC of 0.449 (Xiong et al. 2013). Powar et al. have
also worked on CuCrO 2 using [Co(en)
3 ]
2+/3+ based redox mediators (V OC = 734 mV;
J SC = 1.23 ± 0.17 mA cm
−2 ; FF = 0.53 ± 0.04; η = 0.48 ± 0.08%). Though there is a
comparatively higher V OC value, the value of J SC has been drastically decreased, due
to insufficient hole-injection driving forces. Thus the efficiency was limited (Powar
et al. 2014). Daniel et al. used hydrothermal synthesis to obtain nanocrystals of (Al,
Mg)-Doped CuCrO 2 with smaller size (and therefore larger surface areas) compared
with other delafossites. Doping of Al
3+ causes shifting of the optical band gap by
0.05 eV, while dopic with Mg
2+ causes it to shift by 0.27 eV. In the presence of
Coumarin C343 as the sensitizer, the short-circuit density (J SC ) is increased by 11%
for Al
3+ doping and by 16% for Mg
2+ doping (Daniel et al. 2017).
Ursu Daniela et al. have doped CuCrO 2 with Co to produce non-stoichiometric
nanocrystals using a low-temperature hydrothermal method which increases the oxygen content of the delafossite structure. The electrical resistivity has been decreased
S. Peiris et al.
on CuGaO 2 plates conducted by Zhen Xu et al. produced devices with a remarkably
high J SC = 2.05 mA cm
−2 incorporating I
− /I 3
− electrolyte as the redox mediator.
Nanoplates of 100–200 nm diameter and thickness of 20–30 nm were obtained, and
optimization of temperature for the hydrothermal synthesis was done (Xu et al. 2014).
Adèle Renaud et al. have done further modification to CuGaO 2 based p-DSCs by
doping Mg with assembly of PMI-NDI dyad as the dye, and tris(4,4
-bis-tert-butyl2,2
-bipyridine)cobalt(II/III) as the electrolyte. They found out that there is a 73%
increase in photovoltaic yield compared to undoped CuGaO 2 , when doped with 1%
of Mg. But this performance is lost when the doping is increased above 1% of Mg
(V OC = 305 mV; J SC = 0.415 mA cm
−2 ; FF = 0.35; η = 0.45) (Renaud et al. 2013a).
CuAlO 2 is another type of delafossite which was synthesised by Ahmed and
coworkers under controlled oxygen pressure (pO 2 ) of 105 atm and at a temperature
of 775
° C. A uniform particle size of 35 nm was obtained and cathodic photocurrent
with J SC = 0.954 mA cm
−2 under 1.5 sun illumination (Ahmed et al. 2014). Miclau
et al. have conducted a study based on the effect of polymorphism on photovoltaic
performance of CuAlO 2 delafossite nanomaterials by synthesizing nanocrystalline
3R or mixture of 2H and 3R polytypes. Key factors that cause the formation of poly
types are temperature and autogenous pressure. Even a small concentration of 2H
polytype caused raise energy conversion efficiency by 49% compared to pure 3RCuAlO 2 polytype. The reason for higher efficiencies may be because of the presence
of smaller Cu-Cu distance of 2H polytype compared to that of 3R polytype. As the
electrical conductivity predominantly occurs through the Cu
+ plane, 2H polytype
generates a higher photocurrent density (J SC ) (Miclau et al. 2017).
The first application of hydrothermally synthesised, Mg doped CuCrO 2 delafossite
material in p-DSCs was reported by Xiong et al. They have observed an enhancement
in optical transmittance and reduction of crystallite size, that leads to improvement
of J SC by approximately 27%, when CuCrO 2 was doped with Mg. Lower valence
band edge and faster hole diffusion coefficient has been observed in CuCr 0.9 Mg 0.1 O 2
(in comparison to NiO), producing a V OC of 201 mV and J SC of 1.51 mA cm
−2 . The
efficiency obtained was 0.132% which is nearly three times higher compared to NiObased reference devices with a V OC of 0.449 (Xiong et al. 2013). Powar et al. have
also worked on CuCrO 2 using [Co(en)
3 ]
2+/3+ based redox mediators (V OC = 734 mV;
J SC = 1.23 ± 0.17 mA cm
−2 ; FF = 0.53 ± 0.04; η = 0.48 ± 0.08%). Though there is a
comparatively higher V OC value, the value of J SC has been drastically decreased, due
to insufficient hole-injection driving forces. Thus the efficiency was limited (Powar
et al. 2014). Daniel et al. used hydrothermal synthesis to obtain nanocrystals of (Al,
Mg)-Doped CuCrO 2 with smaller size (and therefore larger surface areas) compared
with other delafossites. Doping of Al
3+ causes shifting of the optical band gap by
0.05 eV, while dopic with Mg
2+ causes it to shift by 0.27 eV. In the presence of
Coumarin C343 as the sensitizer, the short-circuit density (J SC ) is increased by 11%
for Al
3+ doping and by 16% for Mg
2+ doping (Daniel et al. 2017).
Ursu Daniela et al. have doped CuCrO 2 with Co to produce non-stoichiometric
nanocrystals using a low-temperature hydrothermal method which increases the oxygen content of the delafossite structure. The electrical resistivity has been decreased