III. Machine Learning-Assisted Development of Organic Photovoltaics via High-Throughput
3.3 Results and Discussion
3.3.1 Material Selection, Device Application and Characterization
connector in-situ, and deposited on continuously moving substrate. Therefore, a film with a gradient composition could be fabricated by a single deposition process. Further details of the experimental set- up can be seen in Figure 3. 2.
Figure 3. 2. Equipment set up for hot deposition slot die coated R2R processing.
To fabricate devices, the three materials shown in Figure 3. 1b were mixed with various ratios and deposited on a long (typically 6 m per experiment) substrate. Then the film was cut to small pieces for evaporation of MoO3 and Ag with the pattern shown in Figure 3. 1b. We used a hot deposition technique that we previously developed.159, 160 The technique enables high-performance OPV without using problematic additives for polymers with temperature-dependent-aggregation (TDA) behavior.
PM6 was selected as a donor material due to its TDA behavior as well as its high efficiency. Y6 and IT-4F were selected as the combination was the best when this study was started.158
We first confirmed an effect of deposition temperature on performance of devices with each acceptor.
The hot deposition technique requires a heated solution as well as a heated substrate. If the acceptors have different optimum temperature combination, the temperature combination should be considered as a variable for this study. Therefore, glass-based devices were fabricated by hot slot die coating at varied temperature combinations. Fortunately, the PM6:Y6 and PM6:IT-4F combinations showed the best performance at the same temperature combination of 90 °C solution (head) and 130 °C substrate.
J–V characteristics of the devices are shown in Figure 3. 3 and photovoltaic properties are summarized
Coang Direcon Hot Bed
Unwind Rewind
Single/Dual Feed Syringe Pump
Slot Die Head/Bed Temperature
Controller
Hot Head
85
in Table 3. 1.
Figure 3. 3. JV characteristics of slot die coated OPV devices on glass substrates at variable processing temperatures for (a) PM6:IT-4F and (b) PM6:Y6.
Table 3. 1. Summary of photovoltaic parameters of slot die coated OPV devices on glass substrates at variable processing temperatures.
Active Layer Head (oC)
Bed (oC)
JSC
(mA cm-2)
VOC
(V) FF PCE
(%)
PM6:IT-4F
RT
RT 8.33
(7.98±0.35)
0.86 (0.87±0.01)
0.42 (0.42±0.01)
3.02 (2.89±0.13)
60 11.8
(10.9±0.96)
0.88 (0.88±0.00)
0.50 (0.49±0.02)
5.25 (4.65±0.60)
120 11.0
(11.1±1.16)
0.86 (0.84±0.04)
0.64 (0.55±0.09)
6.00 (5.16±0.84)
60
RT 11.3
(11.9±0.55)
0.90 (0.90±0.01)
0.48 (0.44±0.04)
4.89 (4.72±0.17)
60 12.0
(11.3±0.69)
0.88 (0.88±0.01)
0.53 (0.56±0.03)
5.81 (5.68±0.13)
120 13.8
(11.4±2.39)
0.84 (0.85±0.01)
0.52 (0.55±0.03)
6.00 (5.43±0.57)
90
100 11.0
(11.0±0.16)
0.88 (0.88±0.02)
0.48 (0.48±0.01)
4.66 (4.62±0.10)
120 14.6
(13.7±0.82)
0.86 (0.87±0.01)
0.55 (0.54±0.02)
6.85 (6.44±0.41)
130 16.1
(15.4±0.94)
0.88 (0.88±0.02)
0.63 (0.64±0.02)
8.84 (8.55±0.36)
110 130 12.3
(12.2±0.72)
0.86 (0.86±0.01)
0.53 (0.52±0.03)
5.80 (5.50±0.42)
PM6:Y6 RT RT 9.07
(8.45±0.62)
0.76 (0.76±0.00)
0.52 (0.53±0.02)
3.56 (3.38±0.18)
-0.2 0.0 0.2 0.4 0.6 0.8 1.0
-20 -18 -16 -14 -12 -10 -8 -6 -4 -2 0 2
Current density (mA cm-2)
Voltage (V)
RT/RT RT/100
60/100 60/130 90/100 90/130 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2
-16 -14 -12 -10 -8 -6 -4 -2 0 2
Current density (mA cm-2)
Voltage (V)
RT/RT RT/60 RT/120 60/RT
60/60 60/120
90/100 90/120 90/130 110/130
a b
86
100 15.2 (13.7±1.50)
0.80 (0.79±0.03)
0.61 (0.62±0.01)
7.38 (6.64±0.74)
60
100 17.4
(16.9±0.69)
0.80 (0.78±0.02)
0.61 (0.62±0.01)
8.53 (8.23±0.32)
130 18.1
(18.1±0.71)
0.80 (0.79±0.01)
0.62 (0.61±0.01)
9.02 (8.87±0.15)
90
100 18.4
(18.1±0.62)
0.78 (0.78±0.02)
0.65 (0.64±0.05)
9.33 (8.96±0.45)
130 19.4
(19.1±0.76)
0.80 (0.79±0.03)
0.62 (0.63±0.01)
9.69 (9.55±0.14)
* All devices were averaged from 6 devices.
* Active Layer = PM6:IT-4F (1:1.2, w/w) or PM6:Y6 (1:1.2, w/w) in 10 mg ml-1 DCB
Figure 3. 4. An example of dual-feed slot die coated OPV devices. PM6 and Y6:IT-4F (4:1, w/w) solutions were mixed during the deposition and the relative fraction of the acceptors (DDs of acceptors/TDD) is used as x axis. Top x-axis shows physical position of each device relative to the start of the coating. Solid lines exhibit DDs and TDD at the corresponding position.
Using the best temperature combination, we fabricated devices with various ratios and thicknesses.
Figure 3. 4 shows a result of an example of dual-feed deposition. In this case, two acceptors were mixed at the optimized ratio (Y6:IT-4F = 4:1) in the literature.158 Only donor to acceptors ratio was changed gradually by changing flow rates of the solutions at a fixed total flow rate and the in-situ formulated solution was deposited over six-meter substrate. It is noteworthy to mention that slot die coating is classified as a pre-metered method meaning thickness of the film is determined only by solution flow.
There is no loss mechanism in the deposition process47 and therefore the deposition amount of each
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0
2 4 6 8 10 12 14 16 18 20 22
0 5 10 15 20 25 30 35 40
PM6 Y6 IT-4F TDD JSC VOC
FF PCE
DD (Pg cm-2 ) JSC (mA cm-2 )
Acceptors fraction in total (Y6:IT-4F = 4:1) 0.0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
VOC (V)
0.1 0.2 0.3 0.4 0.5 0.6 0.7
Fill factor
0 1 2 3 4 5 6 7 8 9 10
PCE (%)
100 200 300 400 500 600
Coating length (cm)
87
component per unit area can easily be calculated from the flow rate, coating speed/width, and concentration of each component. In this study, we introduce a universal feature, deposition density (DD) and total deposition density (TDD). DD and TDD cover quantitatively absolute amount of each component (e.g. PM6 amount) and total (e.g. sum of PM6, Y6 and IT-4F amounts) solid per unit area, respectively and the unit is μg cm-2. Thus, they provide indirect thickness information and composition ratio of materials at specific coating position.
Figure 3. 5. (a) Schematic illustration of R2R device being coated with a given line speed and coating direction. Flow rate change depending on time and position at (b) type (i) (single feed) and (c) type (ii) and (iii) experiments (dual feed).
The solution flow can be controlled using the differentially pumped syringes with user interface program where the solution flow is represented as flow rate. The flow rate can be consequentially
Period ( ) Period ( )
Flow Rate
Time A'O
A'F
Start Point ( ) Position ( )
Line Speed ( ), Coating Direction
Coating Width ( )
a
Flow Rate
Time Sol. A
Sol. B
Ao BF
Bo AF
b c
Start Point ( )
Flow Rate
Time A'O
A'F
Type (i) Type (i) and (ii)
Start Point ( )
Flow Rate
Time Sol. A
Sol. B
Ao BF
Bo AF
88
customized depending on time by flow rate profile programmed to several mathematical functions. In this study, we selected a linear function as basic flow rate profile. With R2R slot die system, coating position is changed at constant line speed along direction of moving rolls (Figure 3. 5a) so that the flow rate can be calculated depending on coating position with linear functions (Figure 3. 5b, c). In first step, several parameters were considered in calculation procedure as follows:
1)P (sec): Time (Period) it takes for the set initial flow rate to change to the final flow rate.
2)AO or BO (μl min-1): Initial flow rate of solution A or B
3)AF or BF (μl min-1):Final flow rate of solution A or B. In case of single feeding, initial and final flow rate of solution A are denoted as A or A , respectively.
4)S (cm min-1): Coating speed (Line speed) 5)x (cm): Instantaneous coating position
6)I (cm): Initial coating position or deposition offset originated from dead volume of dual-feeding deposition system, it is zero for type (i) experiment and non-zero for type (ii) and (iii) experiments.
7)F (μl min-1): Instantaneous flow rate change of solution 8)C (mg min-1): Concentration of donor/acceptor/blend solution 9)W (cm): Coating width, which is fixed as 1.3 cm in this study.
10)T (μg cm-2): Instantaneous (total) deposition density at specific coating position.
Next, calculation procedures to determine TDD or DD were divided into four steps in the following manner.
1)F depending on coating position
If we only consider F of in type (i) experiment and coating distance change during given period is denoted as , F can be represented as following Eq. (3-1):
2) Substituting with considerable parameters
During given period, coating distance can be calculated at constant line speed.
3) at given coating position with considerable parameters
We can rewrite an equation (1) like below. The flow rate profiles of solution A and B in type (ii) and (iii) experiments can be also obtained in the same manner.
£ Type (i) experiment
(3-1)
(3-2)
89
¤ Type (ii) and (iii) experiment
As the flow profiles of two solutions are symmetrical with each other, and can be replaced with and .
4) at given , and
Device parameters depending on fraction of acceptors (DDs of acceptors/TDD) are shown in the Figure 3. 4. The figure clearly shows how the D:A ratio affects the device parameters. VOC continuously decreased with increased acceptors fraction. It can be seen as an evidence of continuously changing composition along the substrate and composition was controlled as designed. It was obvious that donor- only or acceptor-only composition would not make high-performance devices. However, we designed all experiments to scan through wide parameter space to create training data so that ML can learn what compositions make poor performance as well as high performance. From the experiment, a maximum PCE was 9.69% observed at ~0.54 acceptor fraction (equivalent to D:A = 1:1.16). The result is consistent with the optimized ratio (D:A = 1:1.2) in the literature.158
The films of the example experiment were further analyzed. Figure 3. 6a shows normalized UV-Vis spectra of the films at selected points and expected compositions are color-coded. As the ratio of acceptors increased, absorption region of acceptors in the range of 600–1000 nm158 become more pronounced whereas absorption region of PM6 in the range of 300–700 nm is diminished. At acceptor- dominant composition (D:A1:A2 = 1:54:13), almost no sign in the absorption peak of the donor at 640 nm is shown. Although the spectra clearly show a gradual change of the composition, it would be difficult to judge the compositions quantitively. Therefore, we prepared slot die coated films from pre- mixed solutions (represented as dash lines in the figure) with the compositions at the start, the middle and the end of the R2R produced film for comparison. We found reasonable agreement in terms of the relative peak sizes of PM6 and Y6 and concluded that the composition control was successfully carried
(3-3)
Solution A (3-4)
Solution B (3-5)
(3-6)
90
out.
Figure 3. 6. (a) UV-vis absorption spectra of slot die coated films of PM6:Y6:IT-4F at various blend ratios. Solid lines represent in-situ blended films via dual-feed R2R deposition and dash lines represent batch-processed slot die coated films from pre-mixed blends. (b) J–V characteristics and (c) corresponding IPCE of R2R devices at various donor:acceptor1:acceptor2 (D:A1:A2) ratios.
a
b
c
400 500 600 700 800 900 1000 0.0
0.2 0.4 0.6 0.8 1.0
1.2 1:0:0 1:0.26:0.07 1:0.53:0.13 1:0.93:0.23 1:1.76:0.44 1:4:1 1:54:13 0:0.8:0.2
Normalized Absorption (a.u.)
Wavelength (nm)
-0.2 0.0 0.2 0.4 0.6 0.8
-20 -18 -16 -14 -12 -10 -8 -6 -4 -2 0 2
Current density (mA cm-2 )
Voltage (V)
400 500 600 700 800 900 1000 0
10 20 30 40 50 60
IPCE (%)
Wavelength (nm)
91
Figure 3. 7. AFM (a)(h) height and (i)(p) corresponding phase images of dual-feed slot die coated film on top of PET/ZnO NPs at various D:A1:A2 ratios. All images are 2 μm × 2 μm.
AFM height and phase images were collected at selected composition films to gain insight into the morphological difference modulated by mixing donor and acceptor only solutions. The height and phase images of a donor-only composition (1:0:0) film, as shown in Figure 3. 7a, i, clearly exhibited nanoscale aggregation on its surface and formed smooth films with ro4ot-mean-square (RMS) of 2.46 nm. Figure 3. 7b–e correspond to the height images of 1:0.26:0.07–1:1.76:0.44. Their domains seem to be needle-like in shape, which is slightly different from that of the 1:0:0 film. Nevertheless, nanoscale granular surfaces shown in the donor-only film were also observed. It implies that the crystallization of the donor primarily determines phase separation of the bulk-heterojunction film with a composition of up to 1:2.2 D:A ratio. The RMS values of the films were found to be 2.46–2.72 nm, which are almost the same as that of the donor-only film. These phenomena are similar to previous reports.23, 162 Height images of 1:4:1 and acceptor-dominant composition (1:54:13) films (Figure 3. 7f, g), show irregular
(c) 1:0.53:0.13 (d) 1:0.93:0.23
(e) 1:1.76:0.44 (f) 1:4:1 (b) 1:0.26:0.07 (a) 1:0:0
(g) 1:54:13
15 nm
Rq = 2.46 nm
Rq = 5.52 nm Rq = 2.56 nm Rq = 2.72 nm
Rq = 2.52 nm Rq = 3.06 nm
Rq = 2.63 nm 500 nm
(h) 0:0.8:0.2
Rq = 5.27 nm
(k) 1:0.53:0.13 (l) 1:0.93:0.23
(m) 1:1.76:0.44 (n) 1:4:1 (j) 1:0.26:0.07 (i) 1:0:0
(o) 1:54:13
15 o
500 nm
(p) 0:0.8:0.2
92
and bumpy surfaces due to an excessive amount of acceptors clumping together, lead to an increasing domain size and RMS of 3.06 and 5.52 nm, respectively. The apparent phase separation between donor and acceptors was observed in their phase images, as shown in Figure 3. 7n, o, it would have triggered a reduction in their device performance. A 0:0.8:0.2 film in Figure 3. 7h, p exhibited a similar large phase separation, as well as morphology and RMS values with acceptor-dominant composition films in Figure 3. 7g, o.
Table 3. 2. Summarized photovoltaic parameters of dual-feed R2R slot die coated OPVs at various D:A1:A2 ratios.
PM6:Y6:IT-4F (w/w)
JSC (mA cm-2)
Cal. JSC (mA cm-2)
VOC
(V) FF PCE
(%)
1:0:0 0.40 - 0.88 0.24 0.09
1:0.26:0.07 6.52 5.90 0.84 0.41 2.25
1:0.53:0.13 16.7 16.6 0.82 0.50 6.89
1:0.93:0.23 19.8 19.7 0.80 0.61 9.69
1:1.76:0.44 17.9 17.6 0.78 0.59 8.30
1:4:1 14.0 13.7 0.78 0.50 5.42
1:54:13 3.73 3.14 0.74 0.32 0.89
J–V curves and corresponding IPCE spectra of the devices with corresponding compositions are shown in Figure 3. 6b, c, respectively, and the photovoltaic parameters are summarized in Table 3. 2.
In general, IPCE spectra are not suitable for quantitative analysis of composition as efficiency is affected by charge separation and transport as well as charge generation. Therefore, shapes of the spectra are not well correlated with that of the UV-vis spectra. All spectra of acceptor-rich compositions show similar shape with onset > 950 nm. Even the acceptor-dominant composition shows the peak at 570 nm while majority absorption occurs above 600 nm range. On the contrary, donor-rich composition (1:0.26:0.07) shows the clear feature of the donor. The IPCE spectra are also used to confirm JSC of J–
V measurement and all integrated current values are in good agreement with the corresponding JSC
values as shown in Table 3. 2.
The first example was only comparing donor to acceptors ratio. For full optimization of the ternary blend, the ratio of two acceptors and thickness of the film need to be optimized. Therefore, we conducted three types of experiments: (i) Modulated TDD with a pre-formulated solution. Such experiments show an effect of thickness on performance of a given composition. In this case, only single pump was used. (ii) Modulated Y6:IT-4F ratio at selected TDDs and D:A ratios. (iii) Modulated D:A ratio at selected Y6:IT-4F ratio (4:1) and TDDs. The Figure 3. 4 is belong to type (iii). Such experiments with different Y6:IT-4F ratios and TDDs were carried out. The graphical illustrations are represented in Figure 3. 8. The type (ii) and (iii) experiment should show only composition effect at
93
fixed thickness if the densities of the materials are the same. However, we found minor variations of physical thickness of the films depending on the composition, as shown in Figure 3. 9. The device parameters of experiment type (i)–(iii) are shown in Figure 3. 10–3. 13.
Figure 3. 8. Graphical representation of three experiment types. Green, yellow and pink boxes illustrate the solution conditions and schematic changes of thickness and ratios depending on coating position, which correspond to the three experiment types (Figure 3. 10–3. 13).
Figure 3. 10 shows the effect of TDD (thickness) depending on D:A ratios at the optimum Y6:IT-4F ratio (4:1). All experiments were designed to have a consistent amount of the donor rather than TDD, and therefore the solutions with higher acceptors fraction were scanned through wider TDD ranges with coarse data points. The estimated thickness of 1:1 formulation, based on Figure 3. 9, would be around 50–480 nm, and 25 μg cm-2 TDD would be considered as ca. 200 nm. From the type (i) experiment, we found an interesting trend depending on D:A ratio. Acceptor-rich (1:2) formulation shows highest thickness sensitivity. The optimum point is at 10 μg cm-2 TDD and then FF drops sharply. VOC
consistently decreases with increased TDD. This would be due to poorer charge transporting property and/or increased charge recombinations in the acceptor-rich composition. In contrast, donor-rich formulation (1:0.5) shows the highest thickness tolerance which is an important requirement for large- area printing or commercial production in the future. There is no sign of VOC loss in the thick films of the donor-rich formulation and the optimum TDD (ca. 30 μg cm-2) is higher than other compositions.
However, 1:1.2 formulation was found to be overall best composition with its highest PCE and reasonable thickness tolerance.
PM6 + Y6 + IT-4F
PM6 + Y6
PM6 + IT-4F
PM6 + Y6 + IT-4F
Y6 + IT-4F
PM6 + Y6 + IT-4F
PM6
Thickness
Position
Y6 or IT-4F Fraction
Position
Y6 IT-4F
Thickness
Type (i) Type (ii) Type (iii)
PM6 or Acceptors Fraction
Position
PM6 Acceptors
Thickness
94
Figure 3. 9. Film thickness of dual feeding slot die coated R2R devices at various D:A1:A2 ratios (Figure 3. 5, type (iii) experiment). Top x-axis represents physical positions of each device relative to the start of the coating.
Figure 3. 10. Photovoltaic parameters of the R2R produced OPVs depending on thickness changes of pre-mixed blends at various D:A ratios (fixed Y6:IT-4F ratio at 4:1, w/w)
Figure 3. 11 shows a result of type (ii) experiments. Y6:IT-4F ratio was scanned from 0 to 1 at three different D:A ratios (donor-rich, known optimum ratio, acceptor-rich) with fixed TDD. While 1:1.2 formulation shows the best performance near 0.8 Y6 fraction (i.e. Y6:IT-4F = 4:1), which is consistent with the previous report, we found another peak in IT-4F-rich region. Interestingly, the peak positions were different for each D:A ratio, and the IT-4F-rich region showed even higher performance than Y6- rich region in donor-rich composition. The result clearly shows why wide composition parameters need
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0
50 100 150 200 250 300
Thickness (nm)
Acceptors fraction
Thickness (nm) PM6
Y6 IT-4F TDD
0 5 10 15 20 25 30
DD (Pg cm-2 )
100 200 300 400 500 600
Coating length (cm)
0 20 40 60 80
0 5 10
TDD (Pg cm-2)
PCE (%)
0 20 40 60 80
0.50.6 0.70.8 0.9
TDD (Pg cm-2)
VOC (V)
0 20 40 60 80
0.2 0.4 0.6
TDD (Pg cm-2)
Fill factor
0 20 40 60 80
0 10 20
TDD (Pg cm-2) 1:2 1:1.5 1:1.2 1:1 1:0.75 1:0.5
JSC(mA cm-2)
a
95
to be studied, with the high-throughput system; a critical tool in improving the performance of ternary or quaternary OPVs. Due to practical research limitations, in a typical process one parameter is optimized and then a second parameter is optimized using a fixed first parameter. This introduces a significant problem; the optimized first parameter may not be optimum when the second parameter is changed, as shown in Figure 3. 11. The problem is more pronounced when there are more than four parameters to optimize as the overall trend cannot even be visualized. In this case, ML is essential for analyzing the data.
Figure 3. 11. Photovoltaic parameters of the R2R produced OPVs depending on Y6:IT-4F ratios at various D:A ratios (fixed TDD at ~28.2 μg cm-2). Y6 fraction indicates DD of Y6/DDs of acceptors.
Additional type (ii) experiment was carried out for 1:1.2 composition with much higher TDD of 50 μg cm-2 (ca. 340 nm) to see a trend in thicker films and the results are shown in Figure 3. 12. The thick films showed a same trend of decreased VOC with an increased amount of Y6. However, no ternary blend showed better performance than a binary system in such thick film. It would be due to low electron-transporting property of the mixed acceptors compared to a single acceptor system, which is less critical in thinner films. The benefit from combined absorption of double acceptors would be reduced in such thick film.
Figure 3. 13 shows the results of type (iii) experiments. D:A ratio was scanned from 0 to 1 at various TDDs with fixed Y6:IT-4F ratio of 4:1. The example data shown in the Figure 3. 4 are shown together in Figure 3. 13 for a comparison with other experiments. In this case, performance changes dramatically depending on the D:A ratio so that the optimum composition at each TDD can be seen clearly.
Regardless of TDD, all experiments showed a similar trend with slightly different optimum positions.
The optimum point was in acceptor-rich region for thin film and more donor-rich region for thick film.
The results are consistent with the results from type (i) experiments, i.e. donor-rich composition showing superior performance in thick films.
0.0 0.2 0.4 0.6 0.8 1.0 0.75
0.80 0.85 0.90
Y6 fraction (w/w) VOC (V)
0.0 0.2 0.4 0.6 0.8 1.0 0.40
0.45 0.50 0.55 0.60 0.65
Y6 fraction (w/w)
Fill factor
0.0 0.2 0.4 0.6 0.8 1.0 4.8
6.0 7.2 8.4 9.6
Y6 fraction (w/w)
PCE (%)
0.0 0.2 0.4 0.6 0.8 1.0 15
20
Y6 fraction (w/w)
D:A (1:2)
JSC(mA cm-2)
D:A (1:1.2) D:A (1:0.5)
a
96
Figure 3. 12. (a) JSC, (b) VOC, (c) FF and (d) PCE of the R2R produced OPVs depending on Y6:IT-4F ratios at D:A = 1:1.2 (w/w) (fixed TDD at 50 μg cm-2).
Figure 3. 13. Photovoltaic parameters of the R2R produced OPVs depending on D:A ratios at various thicknesses (fixed Y6:IT-4F ratio at 4:1, w/w).
The ultimate goal of the experiments is to find the best composition from the entire parameter space.
The simplest way would be finding the highest PCE from experimental data and get the composition of the device. However, this way would not find the optimum if the composition was not experimentally
0.0 0.2 0.4 0.6 0.8 1.0
8 10 12 14 16 18
20 D:A (1:1.2)@50 Pg cm-2
JSC (mA cm-2)
Y6 fraction (w/w)
a
0.0 0.2 0.4 0.6 0.8 1.0
0.72 0.74 0.76 0.78 0.80 0.82 0.84 0.86
VOC (V)
Y6 fraction (w/w)
0.0 0.2 0.4 0.6 0.8 1.0
0.35 0.40 0.45 0.50 0.55
Fill factor
Y6 fraction (w/w)
0.0 0.2 0.4 0.6 0.8 1.0
3 4 5 6 7 8
PCE (%)
Y6 fraction (w/w)
b
c d
0.0 0.2 0.4 0.6 0.8 1.0 0
2 4 6 8 10
Acceptors fraction (w/w)
PCE(%)
0.0 0.2 0.4 0.6 0.8 1.0 0.7
0.8 0.9 1.0
Acceptors fraction (w/w)
VOC (V)
0.0 0.2 0.4 0.6 0.8 1.0 0.2
0.3 0.4 0.5 0.6 0.7
Acceptors fraction (w/w)
Fill factor
0.0 0.2 0.4 0.6 0.8 1.0 5
10 15 20
Acceptor fraction (w/w)
50 Pg cm-2 35.6 Pg cm-2 28 Pg cm-2
JSC(mA cm-2)
20 Pg cm-2
a
97
made. Therefore, it would be ideal if the best composition is found by analyzing a trend of performance change in 3D parameter space. Therefore, we collected all experimental data and made a 3D chart by color-coding PCEs, as shown in Figure 3. 14. Six vertically arranged datasets correspond to the type (i) experiments and clearly reflected the thickness variation at each D:A ratio. Four horizontally arranged datasets parallel to Y6 axis correspond to the experiment type (ii). Another four datasets parallel to PM6 axis correspond to the experiment type (iii). Although there are unexplored areas in the 3D space, the experiments were designed to cover as much as practical. Total 2218 devices with about 2200 different compositions are used in the figure. To the best of our knowledge, the number of compositions studied in this work is highest in the history of OPV research.
Figure 3. 14. All composition parameters examined in this study.
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