A Review on Contemporary Hole Transport Materials …
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by one-step method reportedly had higher reproducibility and stability and the efficiency of the device reached up to 16.6%. The highest efficiency for a CuSCN-based
HTM was reported by Lee and et al. (2017) with an efficiency of 17.10% using spray
deposition technique and the use of no additives. It was noted that the conventional
doctor blading technique damages the perovskite layer during the coating process
of CuSCN. The authors reported that the use of this technique made no damage to
the perovskite layer, and the fabricated PSC gave a remarkably long-term thermal
stability with JV characteristics being J sc of 23.1 mA/cm
2 , V oc of 1.013 V, and FF
of 0.731. The lower V oc can be attributed to the use of no additives. Therefore, the
deposition method used in fabrication of HTM layers in PSC plays an important role
in the overall performance of the cell.
4.3 NiO
NiO has been extensively used as an HTM in thin-film structures and mesostructured
scaffold because of its good hole conductivity, deep valence band level −5.3 eV, and
large energy gap (3.5–3.9 eV). The first high-performance PSC based on NiO as HTM
was based on an inverted planar configuration (NiONC/CH 3 NH 3 PbI 3 /PCBM/Al),
and it was fabricated using sol–gel process by Zhu et al. (2014). It was recommended
by the authors that the cells must have high-quality perovskite and sufficient thickness
for NiO nanocrystalline film as a hole transport layer. The efficiency obtained in this
study was 9.11% with J sc 16.27 mA/cm
2 , V oc = 0.882 V, and FF = 0.635. The
efficiency of PSCs using Ni-based HTM was further increased by Kim et al. to
15.4% by doping 5% Cu in HTM (Kim et al. 2015). The J sc and V oc values obtained
were all higher than PEDOT:PSS and NiOx with no doping under similar conditions.
Owing to higher Eg levels, it shows higher V oc levels and appropriate alignment with
high Eg levels found in perovskite. Jung et al. (2015) reported a low-temperature
combustion process to prepare Cu-doped NiOx HTM for high performance. The
films prepared from this method were better than high-temperature sol–gel methods
with an efficiency of 17.7%.
He et al. (2018) recently focussed on post-treatment of NiO hole transport layer
through surface modification by using a trifunctional molecule cysteine (Cys) to
enhance the interfacial contact.
This type of protocol achieved the highest efficiency of 18.3%, gave V oc of more
than 1.12 V and suppressed the hysteresis to negligible.
PSC incorporating 5% Y (yttrium) doped in NiO HTM layer was demonstrated
by Hu et al. 2018. The doping of Y led to lower recombination rate, proper charge
carriers, and enhanced hole mobility. A PCE of 16.31% was achieved with current
density J sc of 23.82 mA/cm
2 .
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by one-step method reportedly had higher reproducibility and stability and the efficiency of the device reached up to 16.6%. The highest efficiency for a CuSCN-based
HTM was reported by Lee and et al. (2017) with an efficiency of 17.10% using spray
deposition technique and the use of no additives. It was noted that the conventional
doctor blading technique damages the perovskite layer during the coating process
of CuSCN. The authors reported that the use of this technique made no damage to
the perovskite layer, and the fabricated PSC gave a remarkably long-term thermal
stability with JV characteristics being J sc of 23.1 mA/cm
2 , V oc of 1.013 V, and FF
of 0.731. The lower V oc can be attributed to the use of no additives. Therefore, the
deposition method used in fabrication of HTM layers in PSC plays an important role
in the overall performance of the cell.
4.3 NiO
NiO has been extensively used as an HTM in thin-film structures and mesostructured
scaffold because of its good hole conductivity, deep valence band level −5.3 eV, and
large energy gap (3.5–3.9 eV). The first high-performance PSC based on NiO as HTM
was based on an inverted planar configuration (NiONC/CH 3 NH 3 PbI 3 /PCBM/Al),
and it was fabricated using sol–gel process by Zhu et al. (2014). It was recommended
by the authors that the cells must have high-quality perovskite and sufficient thickness
for NiO nanocrystalline film as a hole transport layer. The efficiency obtained in this
study was 9.11% with J sc 16.27 mA/cm
2 , V oc = 0.882 V, and FF = 0.635. The
efficiency of PSCs using Ni-based HTM was further increased by Kim et al. to
15.4% by doping 5% Cu in HTM (Kim et al. 2015). The J sc and V oc values obtained
were all higher than PEDOT:PSS and NiOx with no doping under similar conditions.
Owing to higher Eg levels, it shows higher V oc levels and appropriate alignment with
high Eg levels found in perovskite. Jung et al. (2015) reported a low-temperature
combustion process to prepare Cu-doped NiOx HTM for high performance. The
films prepared from this method were better than high-temperature sol–gel methods
with an efficiency of 17.7%.
He et al. (2018) recently focussed on post-treatment of NiO hole transport layer
through surface modification by using a trifunctional molecule cysteine (Cys) to
enhance the interfacial contact.
This type of protocol achieved the highest efficiency of 18.3%, gave V oc of more
than 1.12 V and suppressed the hysteresis to negligible.
PSC incorporating 5% Y (yttrium) doped in NiO HTM layer was demonstrated
by Hu et al. 2018. The doping of Y led to lower recombination rate, proper charge
carriers, and enhanced hole mobility. A PCE of 16.31% was achieved with current
density J sc of 23.82 mA/cm
2 .