18 Interfacial Materials for Organic Solar Cells
393
further noted that the methanol treatment plays an important role in performance
improvement (PCE = 7.97%) by increasing the V bi and passivating surface traps
(Liu et al. 2017).
Fused ring quinacridone derivatives were developed and tested as CIL materials.
Wudl and co-workers reported a water/alcohol soluble quinacridone-based molecule
QHSO 3 Na which when used as CIL increased the device PCE from 4.34 to 5.17%
(Pho et al. 2011). A significant improvement in the FF from 0.53 to 0.63 was observed,
while the V OC and J SC values were similar to the reference cell. Chen et al. demonstrated an improvement in the PCE (6.70%) of PCDTBT:PC 71 BM devices using
4 nm thin QAPyBr CIL containing pyridinium pendent groups due to significant
increase in the FF along with V OC and J SC higher than the Al-based devices (5.13%)
(Chen et al. 2016). Further increase in CIL thickness (~20 nm) the PCE dropped to
around 1.7% due to significant reduction in the J SC and FF. Interestingly, the strong
electron accepting group dicyanomethylene group containing CIL, DCNQAPyBr
showed further improvement in the PCE due to enhanced electron transport ability
and conductivity as well insensitive to thickness of the CIL. The best device gave a
PCE of 6.96% using 13 nm thick DCNQAPyBr. The device gave maintain high PCE
of 5.8% even up to 40 nm thickness showing the importance of cyano groups on the
device performance improvement.
Indacenodithiophene (IDT), which has been successfully employed to develop
various fullerene-free acceptors, was used to synthesize two new cationic electrolyte
TBIDTD and TBIDTCN for CIL. Among the two CILs TBIDTCN gave the better
performance with PCE of 9.19% compared to 8.62% for TBIDTD due to dramatic
reduction of series resistance, lower LUMO energy level for efficient electron transport and extraction (Miao et al. 2018). The reference device gave 1.66 times lower
performance.
18.2.1.3 Fullerene Derivatives as CIL
Various water/alcohol soluble fullerene derivatives have been prepared to use them
as CIL and reviewed recently (Lai et al. 2014; Chueh et al. 2015). Due to similar
energy levels with respect to PC 61 BM/PC 71 BM they have been widely employed
as CIL to modify the surface properties and enhance the photovoltaic performance.
Some representative examples are discussed below and the photovoltaic parameters
are presented in Table 18.2.
Zhang et al. synthesized an alcohol soluble poly(ethylene glycol) end-capped
fullerene derivative, PEGN-C 60 , for its used as EBL with different active layers, such
as P3HT:PC 61 BM, PBDTTT-C:PC 71 BM, and PBDTTT-C-T:PC 71 BM. The optimal
PCEs of the these devices reached values of up to 3.84%, 6.22%, 7.45%, respectively,
and close to the values obtained using Ca/Al based CIL and significantly higher
compared to without EBLs (Zhang et al. 2013).
Li and co-workers prepared two fullerene derivatives namely, PCBDAN and PCBDANI and studied their ability to act as CIL (Li et al. 2013). PCBDANI was synthesized by the reaction of PCBDAN with methyl iodide. These CILs formed interfacial
393
further noted that the methanol treatment plays an important role in performance
improvement (PCE = 7.97%) by increasing the V bi and passivating surface traps
(Liu et al. 2017).
Fused ring quinacridone derivatives were developed and tested as CIL materials.
Wudl and co-workers reported a water/alcohol soluble quinacridone-based molecule
QHSO 3 Na which when used as CIL increased the device PCE from 4.34 to 5.17%
(Pho et al. 2011). A significant improvement in the FF from 0.53 to 0.63 was observed,
while the V OC and J SC values were similar to the reference cell. Chen et al. demonstrated an improvement in the PCE (6.70%) of PCDTBT:PC 71 BM devices using
4 nm thin QAPyBr CIL containing pyridinium pendent groups due to significant
increase in the FF along with V OC and J SC higher than the Al-based devices (5.13%)
(Chen et al. 2016). Further increase in CIL thickness (~20 nm) the PCE dropped to
around 1.7% due to significant reduction in the J SC and FF. Interestingly, the strong
electron accepting group dicyanomethylene group containing CIL, DCNQAPyBr
showed further improvement in the PCE due to enhanced electron transport ability
and conductivity as well insensitive to thickness of the CIL. The best device gave a
PCE of 6.96% using 13 nm thick DCNQAPyBr. The device gave maintain high PCE
of 5.8% even up to 40 nm thickness showing the importance of cyano groups on the
device performance improvement.
Indacenodithiophene (IDT), which has been successfully employed to develop
various fullerene-free acceptors, was used to synthesize two new cationic electrolyte
TBIDTD and TBIDTCN for CIL. Among the two CILs TBIDTCN gave the better
performance with PCE of 9.19% compared to 8.62% for TBIDTD due to dramatic
reduction of series resistance, lower LUMO energy level for efficient electron transport and extraction (Miao et al. 2018). The reference device gave 1.66 times lower
performance.
18.2.1.3 Fullerene Derivatives as CIL
Various water/alcohol soluble fullerene derivatives have been prepared to use them
as CIL and reviewed recently (Lai et al. 2014; Chueh et al. 2015). Due to similar
energy levels with respect to PC 61 BM/PC 71 BM they have been widely employed
as CIL to modify the surface properties and enhance the photovoltaic performance.
Some representative examples are discussed below and the photovoltaic parameters
are presented in Table 18.2.
Zhang et al. synthesized an alcohol soluble poly(ethylene glycol) end-capped
fullerene derivative, PEGN-C 60 , for its used as EBL with different active layers, such
as P3HT:PC 61 BM, PBDTTT-C:PC 71 BM, and PBDTTT-C-T:PC 71 BM. The optimal
PCEs of the these devices reached values of up to 3.84%, 6.22%, 7.45%, respectively,
and close to the values obtained using Ca/Al based CIL and significantly higher
compared to without EBLs (Zhang et al. 2013).
Li and co-workers prepared two fullerene derivatives namely, PCBDAN and PCBDANI and studied their ability to act as CIL (Li et al. 2013). PCBDANI was synthesized by the reaction of PCBDAN with methyl iodide. These CILs formed interfacial