3.2.1. Perovskite thickness
Employing the SCAPS-1D batch study, the effect of perovskite thickness variation was investigated. For this section, the effect of perovskite thickness variation from 100 nm-1000 nm on the photovoltaic parameters and recombination factor are given in the diagrams of Fig. 2 for S3, and Figure SB2-SB5 for S1, S2, S4, and S5 structures. Moreover, the recombination paths of
different absorber thicknesses are given in Figure SB1. (This plot is only given for the perovskite thickness variation and the other recombination path plots are similar to it. Hence, we didn’t present them). As mentioned earlier, the recombination factors that were reported in Fig. 2 and Figure SB2-SB5, are the peaks of the Figure SB1 diagram.
It can be seen from Figure 2 that perovskite thickness increment has a generally positive impact on the performance parameters. Nevertheless, the recombination rate peak will also enhance. This can be justified according to the literature (Bag et al. 2020). As the perovskite thickness increase, the electron- hole generation will enhance, too. On the other side, their recombination probability will raise.
The VOC and JSC refer to the charge’s recombination and generation, respectively. This justifies the behaviors of Figure 2 and Figure SB2-SB5 diagrams. According to the efficiency plot of Figure 2, the efficiency increment rate decreases after the thickness of 500 nm. This helps in selecting the proper thickness regarding the recombination enhancement on the other side. Hence, it seems that the thickness of 500 nm can be an optimum selection for the perovskite thickness.
3.2.2 ETM thickness
Similar to the previous section’s diagrams, the effect of ETM thickness variation was investigated in the thickness range of 40 nm-140 nm. The results are reported in the diagrams of Figure 3 for S3 and Figure SB6-SB9 for S1, S2, S4, and S5 structures.
It can be understood from Figure 3 diagrams’ behavior that enhancing the ETM thickness has a generally negative impact on the performance of PSC. This can be attributed to the late transportation between the absorber and front contact due to the wider distance (Jeyakumar et al. 2020). Moreover, the recombination rate will increase by the thickness enhancement. Figure SB7-SB9 present a similar behavior to Figure 3 and the mentioned justifications can be also applied to them. However, the behavior is completely reversed for the S1 PSC structure demonstrated in Figure SB6. This is certainly because of the difference in absorber between the mentioned optimum structures. However, in the case of S2-S5 structures, according to the more efficiency and less recombination in the thickness of 40 nm, this thickness can be suitable for the optimum selection. This is completely reversed for the S1. Therefore, the thickness of 140 nm was selected.
3.2.3 HTM thickness
Similar to the previous investigations, the HTM thickness effect is considered. For that, the thickness range of 50 nm-400 nm was selected. The results are given in the formats of Figure 4 diagrams for S3 and Figure SB10-SB13 diagrams for S1, S2, S4, and S5 PSC structures.
Despite considerable changes in the previous investigations, as can be seen from Figure 4 and Figure SB10-SB13, no significant changes occur in the performance parameters of PSCs in the considered thickness range of HTMs. It should be noted that despite the ETM layer, the HTM layer does not affect the quality of light absorption by the perovskite layer due to the configurations of PSCs. In other words, light crosses over the ETMs, but it is absorbed by the perovskite layer before reaching the HTM layer. Therefore, electron-hole generation is not influenced by the variation in HTM thickness (Hosseini et al. 2022).
As a summary, the optimum selected thicknesses for the active layers of S1-S5 PSC structures were collected in Table 8.
Table 8- A summary of obtained optimum thicknesses for the active layers of S1-S5 structures
Structure
|
Perovskite optimum thickness
|
ETM optimum thickness
|
HTM optimum thickness
|
S1
|
140 nm
|
400 nm
|
50 nm
|
S2
|
80 nm
|
600 nm
|
50 nm
|
S3
|
40 nm
|
500 nm
|
50 nm
|
S4
|
80 nm
|
600 nm
|
50 nm
|
S5
|
40 nm
|
300 nm
|
50 nm
|
3.2.4 Perovskite doping
The doping density of a layer is another important parameter of a material. It refers to the concentration of impurities in a material. These impurities can be in acceptor or donor types for positive and negative doping, respectively. Hence, the value of doping density has a direct relation with the charge concentration on a material. Therefore, its value will affect the cell’s performance, too.
In the present study, the effect of perovskite doping density was investigated in the doping density range of 1017-1021 1/cm3 for the S3 structure. Figure 5 demonstrates the results in the formats of performance and recombination parameters. A similar task was performed for S2, S4, and S5 structures as indicated in Figure SB14-SB16. (As can be seen in Table 3, the FA0.85Cs0.15PbI3 perovskite layer is an inert material and has equal donor and acceptor densities. Hence, we preferred not to investigate it)
The diagrams of Figure 5 and Figure SB14-SB16 reveal almost similar behaviors with the variation of doping density. The diagrams represent the descending behavior for the performance parameters of the considered structures. This can be attributed to the recombination increment. Enhancing the doping density of the absorber layer helps more generation of charge carriers. However, after a threshold value, it leads to more charge recombination, too. Regarding the obtained results, it seems that the lowest range density is the optimum value for all of the S1-S5 PSC structures utilized in this work.
3.2.5 ETM doping
Similar to the perovskite doping variation, it is better to find the optimum doping densities of transporting layers, too. In this case, the effect of ETM doping variation was investigated in the range of 1015-1022 1/cm3. The results were represented in the forms of Figure 6 diagrams for S3 and Figure SB17-SB20 diagrams for S1, S2, S4, and S5 PSC structures.
According to the diagrams indicated in Figure 6 and Figure SB17-SB20, it can be seen that each of the structures represents different behavior than the others. Therefore, we can’t find any certain behavior for them. However, this uncertainty may have different reasons. It could be due to the SCAPS-1D calculation error in some special doping densities. The difference in active layers among the structures may be another justification for it. However, in the case of the S3 structure, according to the efficiency and recombination plots, we selected the donor density of 1017 1/cm3.
3.2.6 HTM doping
HTM doping is one of the other crucial parameters that affect PSC performance. Regarding the concept that HTM doesn't need to be transparent, the higher values of its doping density can lead to the better transportation of holes to the metal contact. The results of HTM doping density variation in the range of 1015-1022 1/cm3 confirm this subject. The results were reported in Figure 7 diagrams for S3 and Figure SB21-SB24 for S1, S2, S4, and S5 PSC structures.
It is obvious from the mentioned diagrams that, the performance curves of S1-S5 PSC structures possess a generally increasing behavior. On the other side, the recombination plots represent a similar behavior, too. Hence, a decision should be accomplished for the selection of proper doping density for HTM. In the case of S3, it can be seen that after a threshold value, the efficiency doesn’t promote. Therefore, it seems that the value of 1017 1/cm3 can be a suitable choice for HTM doping density. To have a better insight, the optimum values of S1-S5 structures for doping densities of active layers were summarized in Table 9.
Table 9- A summary of obtained optimum doping densities for the active layers of S1-S5 structures
Structure
|
Perovskite optimum doping density
|
ETM optimum doping density
|
HTM optimum doping density
|
S1
|
1.3×1016 1/cm3
|
1016 1/cm3
|
1015 1/cm3
|
S2
|
1016 1/cm3
|
1017 1/cm3
|
1018 1/cm3
|
S3
|
1017 1/cm3
|
1017 1/cm3
|
1017 1/cm3
|
S4
|
1017 1/cm3
|
1017 1/cm3
|
1018 1/cm3
|
S5
|
1017 1/cm3
|
1017 1/cm3
|
1018 1/cm3
|
3.3 Working point optimization
In addition to the mentioned layer parameters that were investigated, some simulation general conditions should be considered regarding their importance. In the following, some of these general conditions will be discussed.
3.3.1 Temperature
Solar cells’ temperature is one of the crucial conditions that should be calibrated properly. Its optimization can help the experimental studies to be performed in more suitable situations. It seems that the simulation process can be employed well in this case. Therefore, in the present case, we selected the temperature range of 300-400 K to find an optimal temperature. The results of Figure 8 for S3 and Figure SB25-SB28 for S1, S2, S4, and S5 indicate the temperature’s effect on the performance parameters of PSCs.
According to the mentioned results of S1-S5 structures, it is obvious that a generally descending behavior can be seen by the increment of temperature. Therefore, selecting the lower temperatures will lead to better performance results. We considered the temperature of 300 K for all of the studied structures. This can be attributed to the higher mobility of charge carriers in high temperatures that lead to more heat dissipation and lower performance.
3.3.2 Series resistance
Solar cells’ operation mechanisms suffer from parasitic resistances existing in their circuits. These resistances include series and shunt ones. They relate to the electrons and holes generation and recombination mechanisms. Generally, series resistance and shunt resistance represent a cell’s resistance to the generation and recombination processes, respectively (Burgelman et al. 2016; Diantoro et al. 2018). The lower and higher values will be the optimum amounts for the series and shunt resistances, respectively. However, in this case, the effect of series resistance was investigated in the range of 0.1-1 Ω.cm2. The results are demonstrated in Figure 9 for S3 and Figure SB29-SB32 for S1, S2, S4, and S5 PSC structures. It should be noted that the mentioned resistances don’t have any special effects on the recombination. Therefore, we preferred not to report them.
As mentioned in the last paragraph, the lower values would be desirable for series resistances. The results of Figure 9 and Figure SB29-SB32 confirm this subject, too.
3.3.3 Shunt resistance
As mentioned earlier, the higher values of shunt resistances are desirable for a solar cell. As the shunt resistance enhances, the cell will approximate more to the ideal solar cell with infinite shunt resistance. To confirm this concept, we considered a relatively vast data range of 102-105 Ω.cm2 for the investigation of the shunt resistance effect. However, after a threshold value, the increment will not be anymore. The diagrams of Figure 10 for S3 and Figure SB33-SB37 for S1, S2, S4, and S5 confirm this subject, too.
To have a better insight, the results of resistances’ optimization were collected in Table 10 for S1-S5 PSC structures.
Table 10- A summary of obtained optimum series and shunt resistances for the active layers of S1-S5 structures
PSC structure
|
Optimum series resistance
(Ω.cm2)
|
Optimum shunt resistance
(Ω.cm2)
|
S1
|
0.1
|
2×104
|
S2
|
0.1
|
2×104
|
S3
|
0.1
|
2×104
|
S4
|
0.1
|
104
|
S5
|
0.1
|
5×103
|
3.3.4 Reflection
In most simulation studies, the reflection parameters are not consumed and the calibrations are far from the real conditions. However, in SCAPS-1D this parameter can be considered, too. The reflection parameter shows the percentage of transmitted light to the absorber layer. It is clear that by the reflection increment, the amount of absorbed light will be decreased. Therefore, it leads to lower performances. The diagrams of Figure 11 for S3 and Figure SB37-SB40 for S1, S2, S4, and S5 PSC structures confirm this. However, on the other side, the lower electron-hole generation can lead to lower recombination, too. Therefore, as represented in the mentioned diagrams, a decrement occurs for recombination plots. Hence, selecting the optimum reflection depends on the object of the study that considers higher performances or lower recombination.
3.4 Configuration optimization
In addition to the mentioned effective factors that should be optimized, the configuration and number of layers in a PSC structure can significantly affect the performance of the cell. Each active layer of a PSC can be configured in single, tandem, or composite forms. So far, all of the investigated parts of the present study are performed in single configurations of the active layers. In other words, only a single material was used for each of the active layers. However, in some cases, more than one material can be employed for each layer. This sometimes can lead to a better performance. In the case of utilizing more than one material for a custom active layer (often two materials), the mentioned layer should be configured in the composite or tandem formats. In the following, the mentioned configurations will be discussed more.
3.4.1 Tandem PSCs
Tandem configuration is one of the common arrangements of PSCs when using more than one material for an active layer. In the case of two different materials for a layer, two various tandem configurations can be formed depending on the placement order of the materials. In the present study, according to the optimum structures’ materials referred to in Table 7, the tandem configuration simulation was accomplished twice for each of the active layers. Depending on the placement order, we named unique abbreviations for each of the active layers' tandem configurations. They include TP1 and TP2 for the perovskite layer, TE1 and TE2 for the ETM layer, and TH1 and TH2 for the HTM layer. Their corresponding structure formation were given in Table 11 with their results of simulation (photovoltaic parameters). It should be noted that each of the tandem layers’ thickness was selected as the half value of the single active layer.
Table 11- photovoltaic parameters upon using tandem structures in active layers
Structure code
|
Structure formulation
|
VOC (V)
|
JSC
(mA/cm2)
|
FF (%)
|
PCE (%)
|
TP1
|
Au/CuSCN/ FASnI3/
FA0.85Cs0.15PbI3/TiO2/FTO
|
1.08
|
26.66
|
61.49
|
17.69
|
TP2
|
Au/CuSCN/FA0.85Cs0.15PbI3/
FASnI3/TiO2/FTO
|
1.04
|
3.24
|
82.12
|
2.76
|
TE1
|
Au/CuSCN/ FASnI3/
PCBM/TiO2/FTO
|
1.13
|
28.26
|
84.58
|
26.93
|
TE2
|
Au/CuSCN/ FASnI3/ TiO2/
PCBM/ FTO
|
1.12
|
26.43
|
83.16
|
24.57
|
TH1
|
Au/CuSCN/Spiro- OMeTAD/FASnI3/TiO2/FTO
|
1.13
|
28.23
|
83.51
|
26.56
|
TH2
|
Au/Spiro-OMeTAD/ CuSCN/FASnI3/TiO2/FTO
|
1.13
|
28.23
|
83.64
|
26.60
|
According to the results of the tandem structures' simulation, it can be seen that employing two absorbers in the tandem format has a negative impact on the performance of the cell. For instance, the efficiency results of TP1 and TP2 structures are considerably lower than their similar single S1 and S3 PSC structures. In the case of ETM, it can be seen from Table 7 that TE1 and TE2 structures are the mixture formats of single S2 and S3 structures. The efficiency results reveal that the TE1 structure possesses the most efficiency among the mentioned structures. Moreover, the efficiency value of TE2 is between S2 and S3 structures’ efficiencies. Therefore, it seems that choosing the TE1 tandem structure will be a proper selection. Similar to the ETM tandem selection, the results of HTM tandems represent better efficiencies for both TH1 and TH2 tandem structures relative to their corresponding single structures (S3 and S5). However, regarding a little difference, we can select the TH2 structure as the optimum one.
It should be noted that the reported results were given in only a custom thickness for the tandem layers. For more comparison, it is better to consider more range of thicknesses for the studied tandem layers. For that, a more complete study was accomplished using the batch simulation of SCAPS-1D for different thicknesses of the active layers. The results are collected in Table 12-14 for perovskite, ETM, and HTM layers. The thickness range was considered 100-500 nm for each tandem perovskite, 20-100 nm for each tandem ETM, and 50-250 nm for each tandem HTM.
Table 12- photovoltaic parameters upon using different thicknesses of tandem absorbers
FASnI3
thickness (nm)
|
FA0.85Cs0.15PbI3
thickness (nm)
|
JSC
(mA/cm2)
|
VOC (V)
|
FF (%)
|
PCE (%)
|
Recombination rate peak (1/cm3)
|
100
|
100
|
19.36
|
1.09
|
67.24
|
14.13
|
5.90×1018
|
100
|
200
|
22.29
|
1.07
|
63.20
|
15.10
|
4.41×1018
|
100
|
300
|
24.01
|
1.06
|
60.76
|
15.51
|
3.28×1018
|
100
|
400
|
25.06
|
1.06
|
58.94
|
15.61
|
2.56×1018
|
100
|
500
|
25.74
|
1.05
|
57.41
|
15.57
|
2.11×1018
|
200
|
100
|
23.74
|
1.09
|
67.11
|
17.44
|
1.84×1019
|
200
|
200
|
25.26
|
1.08
|
62.92
|
17.20
|
1.34×1019
|
200
|
300
|
26.19
|
1.07
|
60.36
|
16.97
|
1.01×1019
|
200
|
400
|
26.79
|
1.07
|
58.48
|
16.73
|
8.00×1018
|
200
|
500
|
27.18
|
1.07
|
56.93
|
16.48
|
6.71×1018
|
300
|
100
|
26.24
|
1.10
|
67.20
|
19.33
|
3.12×1019
|
300
|
200
|
27.07
|
1.08
|
62.93
|
18.47
|
2.29×1019
|
300
|
300
|
27.60
|
1.08
|
60.31
|
17.92
|
1.76×1019
|
300
|
400
|
27.95
|
1.07
|
58.37
|
17.49
|
1.43×1019
|
300
|
500
|
28.18
|
1.07
|
56.78
|
17.11
|
1.22×1019
|
400
|
100
|
27.72
|
1.10
|
67.32
|
20.44
|
4.21×1019
|
400
|
200
|
28.20
|
1.08
|
63.02
|
19.27
|
3.15×1019
|
400
|
300
|
28.53
|
1.08
|
60.34
|
18.54
|
2.46×1019
|
400
|
400
|
28.74
|
1.07
|
58.38
|
18.00
|
2.04×1019
|
400
|
500
|
28.89
|
1.07
|
56.75
|
17.55
|
1.76×1019
|
500
|
100
|
28.62
|
1.09
|
67.43
|
21.11
|
5.08×1019
|
500
|
200
|
28.93
|
1.08
|
63.12
|
19.79
|
3.87×1019
|
500
|
300
|
29.15
|
1.08
|
60.41
|
18.96
|
3.08×1019
|
500
|
400
|
29.29
|
1.07
|
58.42
|
18.36
|
2.58×1019
|
500
|
500
|
29.39
|
1.07
|
56.78
|
17.87
|
2.26×1019
|
Table 12 represents the list of photovoltaic parameters and recombination factor values for different thicknesses of perovskite tandem materials. A simple look can give the highest efficiencies and the lowest recombination. However, the results do represent not any data with the highest efficiency and the lowest recombination, at the same time. For instance, the thicknesses of 500 nm for FASnI3 and 100 nm for FA0.85Cs0.15PbI3 reports the highest efficiency. However, it represents the highest recombination, too. In other data, the thicknesses of 100 nm for FASnI3 and 500 nm for FA0.85Cs0.15PbI3 gives the lowest recombination, but it doesn’t possess a relatively suitable performance. Therefore, depending on the project object, the optimum result can be extracted.
Table 13-photovoltaic parameters upon using different thicknesses of tandem ETMs
PCBM
thickness (nm)
|
TiO2
thickness (nm)
|
JSC
(mA/cm2)
|
VOC (V)
|
FF (%)
|
PCE (%)
|
Recombination
rate peak (1/cm3)
|
20
|
20
|
28.29
|
1.13
|
84.66
|
26.97
|
5.64×1019
|
20
|
40
|
28.25
|
1.13
|
84.38
|
26.84
|
5.51×1019
|
20
|
60
|
28.22
|
1.13
|
84.21
|
26.76
|
5.32×1019
|
20
|
80
|
28.20
|
1.13
|
84.13
|
26.71
|
5.12×1019
|
20
|
100
|
28.18
|
1.13
|
84.09
|
26.67
|
5.07×1019
|
40
|
20
|
28.32
|
1.13
|
83.69
|
26.67
|
5.1×1019
|
40
|
40
|
28.29
|
1.12
|
83.26
|
26.50
|
4.87×1019
|
40
|
60
|
28.26
|
1.12
|
83.07
|
26.40
|
4.77×1019
|
40
|
80
|
28.22
|
1.12
|
83.02
|
26.35
|
4.76×1019
|
40
|
100
|
28.19
|
1.12
|
83.01
|
26.32
|
4.76×1019
|
60
|
20
|
28.37
|
1.12
|
81.90
|
26.12
|
4.58×1019
|
60
|
40
|
28.30
|
1.12
|
81.53
|
25.93
|
9.54×1019
|
60
|
60
|
28.25
|
1.12
|
81.36
|
25.82
|
1.27×1020
|
60
|
80
|
28.21
|
1.12
|
81.32
|
25.77
|
1.34×1020
|
60
|
100
|
28.18
|
1.12
|
81.31
|
25.74
|
1.36×1020
|
80
|
20
|
28.25
|
1.12
|
80.02
|
25.38
|
2.82×1020
|
80
|
40
|
28.14
|
1.12
|
79.72
|
25.18
|
4.12×1020
|
80
|
60
|
28.08
|
1.12
|
79.57
|
25.08
|
4.54×1020
|
80
|
80
|
28.04
|
1.12
|
79.54
|
25.03
|
4.63×1020
|
80
|
100
|
28.00
|
1.12
|
79.54
|
25.00
|
4.64×1020
|
100
|
20
|
27.89
|
1.12
|
78.37
|
24.52
|
7.32×1020
|
100
|
40
|
27.75
|
1.12
|
78.15
|
24.32
|
8.65×1020
|
100
|
60
|
27.68
|
1.12
|
78.04
|
24.22
|
9.05×1020
|
100
|
80
|
27.64
|
1.12
|
78.02
|
24.17
|
9.13×1020
|
100
|
100
|
27.61
|
1.12
|
78.02
|
24.14
|
9.13×1020
|
Selecting the proper thicknesses for tandem ETMs is not as difficult as in the perovskite case as can be seen from Table 13. The data represents the highest performance and almost the lowest efficiency for the 20 nm thicknesses for both of the tandem ETMs. Therefore, it can be a suitable choice for the selection.
Table 14-photovoltaic parameters upon using different thicknesses of tandem HTMs
CuSCN
thickness (nm)
|
Spiro- OMeTAD
|
JSC
(mA/cm2)
|
VOC (V)
|
FF (%)
|
PCE (%)
|
Recombination
rate peak (1/cm3)
|
|
thickness (nm)
|
|
|
|
|
|
50
|
50
|
28.23
|
1.13
|
83.53
|
26.57
|
6.12×1019
|
50
|
100
|
28.23
|
1.13
|
83.53
|
26.57
|
6.12×1019
|
50
|
150
|
28.23
|
1.13
|
83.53
|
26.57
|
6.12×1019
|
50
|
200
|
28.23
|
1.13
|
83.53
|
26.57
|
6.12×1019
|
50
|
250
|
28.23
|
1.13
|
83.53
|
26.57
|
6.12×1019
|
100
|
50
|
28.23
|
1.13
|
83.18
|
26.45
|
6.13×1019
|
100
|
100
|
28.23
|
1.13
|
83.18
|
26.45
|
6.13×1019
|
100
|
150
|
28.23
|
1.13
|
83.18
|
26.45
|
6.13×1019
|
100
|
200
|
28.23
|
1.13
|
83.18
|
26.45
|
6.13×1019
|
100
|
250
|
28.23
|
1.13
|
83.18
|
26.45
|
6.13×1019
|
150
|
50
|
28.23
|
1.13
|
82.83
|
26.34
|
6.14×1019
|
150
|
100
|
28.23
|
1.13
|
82.83
|
26.34
|
6.14×1019
|
150
|
150
|
28.23
|
1.13
|
82.83
|
26.34
|
6.14×1019
|
150
|
200
|
28.23
|
1.13
|
82.83
|
26.34
|
6.14×1019
|
150
|
250
|
28.23
|
1.13
|
82.83
|
26.34
|
6.14×1019
|
200
|
50
|
28.23
|
1.13
|
82.49
|
26.23
|
6.15×1019
|
200
|
100
|
28.23
|
1.13
|
82.49
|
26.23
|
6.15×1019
|
200
|
150
|
28.23
|
1.13
|
82.49
|
26.23
|
6.15×1019
|
200
|
200
|
28.23
|
1.13
|
82.49
|
26.23
|
6.15×1019
|
200
|
250
|
28.23
|
1.13
|
82.49
|
26.23
|
6.15×1019
|
250
|
50
|
28.23
|
1.13
|
82.14
|
26.12
|
6.16×1019
|
250
|
100
|
28.23
|
1.13
|
82.14
|
26.12
|
6.16×1019
|
250
|
150
|
28.23
|
1.13
|
82.14
|
26.12
|
6.16×1019
|
250
|
200
|
28.23
|
1.13
|
82.14
|
26.12
|
6.16×1019
|
250
|
250
|
28.23
|
1.13
|
82.14
|
26.12
|
6.16×1019
|
Similar to the HTM thickness variation effect investigation for single configurations, it can be seen from Table 14 that this also applies to the tandem arrangements. However, regarding a little difference, we can select the 50 nm thicknesses for both of the considered HTMs.
3.4.2 Composite PSCs
In addition to the simulation of simple planar PSC structures, SCAPS-1D has the capability of composite layers’ structure simulation. Similar to the tandem cases, the simulators can consider composite configurations for each layer. For example, in the case of the perovskite layer, themixture or composition of two perovskite materials (e.g., Table 7 materials) can be employed instead of a tandem arrangement. In the case of composite configurations, the composition of materials in the mixture is an important factor. Therefore, similar to the previous investigations, we considered the impact of active layers’ composition on the performance and recombination parameters of PSCs. The results were demonstrated in Figure 12-14 for the active layers.
As can be seen from Figure 12, enhancing the composition of FA0.85Cs0.15PbI3 has a negative effect on the performance of FA0.85Cs0.15PbI3/FASnI3-based PSCs. Therefore, it seems that utilizing a single FASnI3-based perovskite can give better performances and the composite configuration didn’t report acceptable results.
Similar to the perovskite composite results, the diagrams of the PCBM composition effect in the PCBM/TiO2 mixture indicated in Figure 13, possess a generally descending behavior. Hence, selecting the low values for PCBM composition is desired. However, considering the little differences, we selected 25% composition for PCBM and 75% for TiO2.
According to Figure 14 diagrams, it can be seen that the Spiro-OMeTAD composition variation has not any significant effect on the performance parameters of Spiro-OMeTAD/CuSCN-based PSC. However, in the composition of 100% for Spiro-OMeTAD (single Spiro-OMeTAD), the results are significantly lower than the others. Generally, by very little difference, we selected 80% composition for Spiro-OMeTAD.
3.5 Final I-V results
To possess better insights, it is better to summarize the obtained results. For this, the photovoltaic parameters of different configurations from the primary run to the mixed composite-tandem structures were collected in Table 15. As a summary of previous investigation for S3 PSC structure, it seems that the single FASnI3 configurations for perovskite, tandem arrangement for ETM, and composite structure for HTM reveal the optimum efficiency for each case. Therefore, we decided to consider all of them in a single simulation as the final step.
Table 15- photovoltaic parameters of different PSC configurations for S3 structure
Structure mode
|
Status
|
VOC (V)
|
JSC
(mA/cm2)
|
FF (%)
|
PCE (%)
|
single
|
Primary run
|
1.13
|
27.75
|
83.16
|
26.02
|
single
|
Results after property optimization
|
1.13
|
28.23
|
83.86
|
26.67
|
Tandem
|
Best perovskite tandem (TP1)
|
1.08
|
26.66
|
61.49
|
17.69
|
Tandem
|
Best ETM tandem (TE1)
|
1.13
|
28.26
|
84.58
|
26.93
|
Tandem
|
Best HTM tandem (TH2)
|
1.13
|
28.23
|
83.64
|
26.60
|
composite
|
Best ETM composite (0.75 TiO2, 0.25 PCBM)
|
1.13
|
28.23
|
84.14
|
26.70
|
composite
|
Best HTM composite (0.8 Spiro-OMeTAD, 0.2 CuSCN)
|
1.13
|
28.23
|
84.14
|
26.76
|
Tandem/ composite
|
Best PSC structure (single perovskite, tandem ETM- TE1, composite HTM-0.8 Spiro-
OMeTAD, 0.2 CuSCN)
|
1.13
|
28.29
|
84.94
|
27.07
|
According to Table 15 results, it can be seen that all of the optimization steps including layer property, work points, and configuration optimizations have a positive impact on the general performance of basic considered PSCs (S1-S5). The total efficiency was increased by about 1%. However, it should be noted that in this study the recombination factor was considered in addition to the performance factors during the optimization processes and this led to lower efficiency increments. To have a better insight, the total I-V curves of different processes are given in Figure 15.
The area under the I-V curve of a solar cell represents its performance. It is obvious from the given I-V plots that this area was increased by more progression of the optimization processes. This confirms the total positive process of the present work.