Samples fabricated for exciton dynamic investigation

power from 0.001 to over 1sun.

The value of sun can be accurately measured and calibrated by a silicon diode (Model 99150 V). By tuning the wanted sun value detected by reference cell, our solar cells were replaced on the holder. All the measurements were taken under the dark room to preventing the noise from the environment, especially under low intensity measurement. And to avoid the thermal formation during the measurement, each test will place over 1 min to cool down when the measurement is too frequently.

The system is also supported by Prof. Tian Lung Chiu in Yuan Ze University, Taoyuan Taiwan

Fig. 2-5 Set up of Sun variation system

2.3 Sample fabrication and measurement systems for exciton

dynamics

2.3.1 Samples fabricated for exciton dynamic investigation

All the samples were fabricated under the same evaporation system as mentioned in section 2.2.2. Rubrene and LiF thin film were deposited on the quartz and glass substrates under high vacuum, which the quartz purity over 99.99% and the

24

transmission also greater than 95% in visible region. The samples then transfer to the nitrogen glove box to seal it with UV glues.

2.3 2 Steady state and time-resolve photoluminence (TrPL) at different temperatures

In this research, exciton dynamic was studied by the measurement of steady state photoluminence and TrPL. The system is established and supported by Dr. Pin-Hao Sher from Prof. Juen-Kai Wang's group in Institute of Atomic and Molecular Sciences, Academia Sinica, Taiwan and the detail construction was shown in Fig. 2- 6.

A Nd:VAN (High Q IC-1064-15000) laser source with 1064 nm emission wavelength was employed in this research. Laser pulsewidth was 6.5 ps in full width at half maximum (FWHM) with its origin repetition rate 76 MHz. The pulse passed through a second harmonic generation (SHG) crystal which generated 532 nm pulses.

Then the radio frequency (RF) acoustic pulse selector changed the repetition rate by by producing a periodic wave grating to reflect the unwanted pulses. The repletion rate we chose was 170 kHz. A first 4X lens and aperture served the function of space filter to eliminate the frequency noise from the light source. A combination for half wave plate and broad band polarizer (SM1PM10) was used to vary the input intensity.

By using the power meter diode (818-UV) and optical power meter (1916C, Newport) before the microscope, an accurate intensity density (in terms of W) can be measured. It can monitor and focus the sample by microscope (Olympus BX61W1) in front of sample. After passing the long pass filter, the reflecting fluorescence signal coming from samples went through the same path and back to the detector. To detect the signal, one can obtain the steady state behavior by detecting the signals with Charge-coupled Device (CCD) (Andor DU920P BR-DD) or transient characteristic by Time-Correlated Single Photon Counting (TCSPC) system with reverse mode to delay

25

the time, all the fluorescence was collected by monochromator (Horiba Jobin Yvon MicroHR).

Fig. 2-6 Set up of steady state and time-resolve photoluminence (TrPL) In our measurement, samples were mounted on a stage with temperature control system from 77K to room temperature. Here, samples attached to the special cryo carrier (Cryo industries CFM 1738-X6M102, 5119) as illustrated in Fig. 2-7. To provide a better thermal conduction, silver glue was applied between copper holder in cryo carrier and samples. The base pressure of the measurement chamber is 1×10^-5 by turbo pump (Varian vacuum tec TPS-compact). Liquid nitrogen was used to cool down the system to 77 K. Under the temperature controller (Lakeshore 331), the heater can control the temperature in carrier.

26

Fig. 2-7 Temperature-controlled sample holder.

27

3 Chapter 3 Optimization of bulk heterojunction OSC for

D-A-A configuration molecule with single cyano group as

the electron donor material

3.1 Introduction

In this chapter, four novel p-type electron donor materials, DTCPB, DTCTB, DTCPBO and DTCTBO were investigated and fabricated into OSC. These compounds were synthesized and supported by Prof. Keng-Tsung Wong’s group, Department of Chemistry, National Taiwan University. Compared with the previous work⁸⁶, dicyanovinylene (DCV) groups were replaced by single cyano in our study to provide larger ΔELUMO between electron donor and acceptor materials, which improves exciton dissociation at donor/acceptor interface and reduce recombination.

With systematically engineering the OSC device structures based on these four electron donor materials and C60 and C70 as the electron acceptor materials, we found that the optimized ones were bulk heterojunction due to their superior FF values. In our optimized device structures, power conversion efficiencies of DTCPB, DTCTB, DTCPBO and DTCTBO based OSCs were 6.55%, 4.40%, 5.98%, 4.65%, respectively.

Incident illumination power was varied for studying the recombination characteristics of OSCs with different electron donor materials.

3.2 Photophysical properties of the four single cyano group electron

28

donor materials

Fig. 3-1 Molecular structures of (a) DTCTB, (b) DTCPB, (c) DTCPBO, (d) DTCTBO and (e) DTDCPB.

Fig. 3-1 shows the molecular structures of DTCPB, DTCTB, DTCPBO and DTCTBO, respectively, which were originally modified from the compound 2-{[7-(4-N, N-ditolylaminophenylen-1-yl)-2,1,3-benzothiadiazol-4-yl]methylene}

malononitrile (DTDCPB), as shown in Fig. 3-1 (e). All these organic materials were synthesized by Prof. Keng-Tsung Wong’s group. With connecting a single cyano moiety attached as the electro-withdrawing end-group, LUMO value can be easily raised up (1 eV higher than acceptor) while maintaining a HOMO value which provides a suitable D-A electro-withdrawing ability compared to an over-strong one

29

in DTDCPB to prevent the formation of dipoles. The entire chemical configuration for four compounds with single cyano groups were shown in Fig. 3-1 However, there is one disadvantage for these four materials that the wide bandgap characteristics (higher LUMO with the same HOMO, compared to DTDCPB) results in blue-shift in absorption spectra combined with the lower absorption ability.

The differences between these four compounds are illustrated below: from the electron donor endcap, the electron-rich and fortified quinoidal characters of thiophene functional groups of DTCTB and DTCTBO result in the redshift (50-70 nm) in absorption spectra, compared to phenelyne attached molecules, DTCPB and DTCPBO. Then, considering the central bridging electron-withdrawing unit, benzoxadiazole (BO) and benzothiadiazole (BT), absorption spectra of BO-based molecules (DTCPBO and DTCTBO) are redshifted compared to those of BT-based ones (for DTCPB and DTCTB).and the HOMO levels were also deep-lying. Fig. 3-2 shows the absorption spectra of these four molecules in solution (CH3Cl) and thin films (by thermal evaporation).

Fig. 3-2 Absorption spectra of the four molecules (a) in solution, and (b) thin films.

The absorption peak for DTCPB, DTCPBO, DTCTB and DTCTBO are 491, 518, 563 and 583 nm for solution and 511, 537, 583, 600 nm for thin film, respectively.

30

HOMO values of these thin film measured by photoelectron spectrometer are shown in Fig. 3-3. The phenylene-containing groups help to lower the HOMO value respect to thiophene by ~0.1 eV, this shows a similar result in BO and BT moiety. All the parameters and thermal properties for intrinsic parameters were reorganized in the Table. 3-1 and Table. 3-2.

Fig. 3-3 HOMO of DTCPB, DTCPBO, DTCTB and DTCTBO thin films measured by photoelectron spectrometer.

Table. 3-1 Basic characteristics of DTCPB, DTCPBO, DTCTB and DTCTBO in solution.

Table. 3-2 Basic characteristics of DTCPB, DTCPBO, DTCTB and DTCTBO

31

3.3 OSC optimization of four electron donor materials with single

cyano substituent molecules

In this section, we illustrate the optimization procedures of OSCs by using these four electron donor materials with C60 and C70 electron acceptors. We optimized DTCTB first, followed by DTCPB, DTCPBO, and finally DTCTBO in sequence. In our previous research, we found that the optimized OSC structure consisted of an active layer and an electron transport layer (planar-mixed heterojunction structure, PMHJ)⁸⁵. Besides, donor buffer layer between anode and active layer can effectively prevent exciton quenching and increase J_SC and PCE in OSCs. Hence, we started our device architecture from PMHJ. However, interestingly, in OSCs based on these four electron donor materials, device performances were even better when using simple bulk-heterojunction (BHJ) structure. Besides, insertion of donor buffer layer showed worse efficiency in these OSCs. Hence, the device structure was very simple with two variables, mixing ratio and active layer thicknesses.

In our devices, we used MoOx and bathocuproine (BCP) as the hole extraction layer and exciton blocking layer, respectively. The workfunctions of electrodes and energy levels of materials were shown in Fig. 3-4.

32

Fig. 3-4 Energy diagrams of four single cyano groups moieties molecules with C60 and C70 under simple bulk heterojunction

3.3.1 Comparison between PMHJ and BHJ of DTCTB devices

3.3.1.1 C

₆₀

based OSC

First of all, we fixed our thickness of active region to 60 nm by changing the ratio thickness between mixing layer and acceptor C₆₀. In such a design, the optical field distribution did not change a lot. The mixing ratio was fixed at 1:1.6 ^[85].

Table. 3-3 Device configurations from A-1 to A-4 of DTCPB:C60 OSC. The unit is nm.

Device MoO₃ DTCTB:C₆₀ C₆₀ BCP Al

A-1

20

1:1.6 (Mixing ratio), 20 40

7 100

A-2 1:1.6 (Mixing ratio), 30 30

A-3 1:1.6 (Mixing ratio), 40 20

A-4 1:1.6 (Mixing ratio), 50 10

33

J-V characteristic of devices from A-1 to A-5 under dark condition and 1-sun AM 1.5 G solar illumination was shown in Fig. 3-5 and the device performance was shown in Table. 3-4. As the thickness of mixing layer increased, J_SC increased, RS decreased, and PCE increased, which meant C60 layer should be as thin as possible.

(a) (b)

Fig. 3-5 J-V performances of devices from A-1 to A-4 under (a) dark condition and (b) 1-sun solar illuminations.

Table. 3-4 Performances of devices from A1 to A-4 under 1-sun solar

34

(a) (b)

(c)

Fig. 3-6 (a) EQE, (b) IQE and (c) absorption spectrum of devices from A-1 to A-4.

3.3.1.2 C

₇₀

based OSC

Here, we attempt to apply another acceptor, C₇₀ to enhance our PCE. In our previous work⁸⁵, although C70 can induce a higher JSC, the electrical property was poor compared to C₆₀ so we can introduce a transporting by higher mobility C₆₀ while mixture with C70. In this section, we varied the transporting layer as C60 or C70, or give a replacement with a mixing layer for preventing from the variation of optical field distribution, in other words, to compare the PMHJ and BHJ in C70 system.

35

Devices configurations and performances were shown in Table. 3-5 and Table. 3-6.

The J-V performances for devices of A-5 to A-7 under dark condition and illuminations were shown in Fig. 3-7

Table. 3-5 Device configurations from A-5 to A-7 of DTCPB:C₇₀ OSC. The unit is nm.

Fig. 3-7 J-V performances of devices from A-5 to A-7 under (a) dark condition and (b) 1-sun solar illuminations.

Table. 3-6 Performances of devices from A-5 to A-7 under 1-sun solar

36

A-7 0.75 9.63 47.02 3.41 0.44 15.90

Among these three devices, one can see that BHJ device (A-7) exhibited highest RSH, FF, and PCE, which meant the introduction of acceptor layer (C60 or C70) resulted in carrier accumulation and carrier recombination.

(a) (b)

(c)

Fig. 3-8 (a) EQE, (b) IQE and (c) absorption spectrum of devices from A-5 to A-7.

3.3.2 Optimization of different mixing ratio and thickness of active

layer for DTCTB

37

3.3.2.1 C

₆₀

based OSC

Then, we tuned the mixing ratio of electron donor and acceptor material, as shown in Table 3-7. J-V characteristic of devices to under dark condition and 1-sun AM 1.5 G solar illumination was shown in Fig. 3-9 and performances were shown in Table. 3-8. One can see that the optimized mixing ratio is DTCTB:C₆₀ = 1:2.2 (A-10).

Comparing devices A-10 and A-13, C60 neat acceptor layer should be replaced by mixing layer for improving PCE.

Table. 3-7 Devices configuration of devices from A-4, A-8 to A-13. The unit is nm.

Device MoO₃ DTCTB:C₆₀ C₆₀ BCP Al

A-4 1:1.6 (Mixing ratio), 50 10

100 A-8 1:1.6 (Mixing ratio) , 60 10

A-9 1:1.9 (Mixing ratio) , 60 10

A-10 1:2.2 (Mixing ratio) , 60 10 7

A-11 1:2.4 (Mixing ratio) , 60 10

A-12 1:2.5 (Mixing ratio) , 60 10

A-13 1:2.2 (Mixing ratio) , 70 0

(a) (b)

Fig. 3-9 J-V performances from of device A-4 to A-12 under (a) dark condition

38

and (b) 1-sun solar illuminations.

Table. 3-8 Performances of devices from A-4, A-8 to A-13 under 1-sun solar

39

(b) (c)

Fig. 3-10 (a) EQE, (b) IQE and (c) absorption spectrum of devices A-8 and A-13.

3.3.2.2 C

₇₀

based OSC

In this section, we optimize the DTCTB: C₇₀ by varying the mixing ratio and thickness. The optimized condition is DTCTB: C70 = 1: 2.6 with the thickness of 70 nm, as shown in Fig. 3-10 and 3-11 and Tables 3-9 and 3-10.

Table. 3-9 Device configurations for different ratio and thickness of active layer of A-7, A-14 to A-17 of DTCTB:C₇₀ based OSC. The unit is nm.

Device MoO₃ DTCTB:C₇₀ C₇₀ BCP Al

A-7

20

1:2.2 (Mixing ratio) , 70

0 7 100

A-14 1:2.6 (Mixing ratio) , 70 A-15 1:3.0 (Mixing ratio) , 70 A-16 1:2.6 (Mixing ratio), 60 A-17 1:2.6 (Mixing ratio), 80

40

(a) (b)

Fig. 3-11 J-V performance of devices from 3-20 to 3-22 under (a) dark condition and (b) 1-sun solar illuminations.

Table. 3-10 Devices performance of different mixing ratio and thickness of active layer for DTCPB/ C70 based OSC.

Name VOC

41

(a) (b)

(c) (d)

(e) (f)

Fig. 3-12 (a) EQE, (b) IQE and (c) absorption spectrum of devices A-7, A-14 to A-15 with different mixing ratio and (d) EQE, (e) IQE and (f) absorption spectrum of devices from A-14, A-16 to A-17 with different thickness of active layer.

42

3.3.2.3 Replacement of different blocking layer for DTCTB: C

₆₀

based OSC

Here, we employed several kinds of blocking layer in order to block the exciton from anode side and promote the hole transport ability. These blocking layer showed different HOMO values in Fig. 3-13. The devices configurations and detail performances were also present in Table. 3-11 and Table. 3-12, respectively. The J-V performances for devices from A-18 to A-25 under dark condition and illuminations were shown in Fig. 3-14. However, the insertion of blocking layer resulted in higher R_S, and little enhancement (if any) on J_SC, which resulted in worse PCE.

Table. 3-11 Device configurations for different blocking layers applied on champion device for DTCTB:C60 based OSC. The unit is nm.

Device MoO3 Blocking layer DTCTB:C60 C60 BCP Al

43

Fig. 3-13 Configurations of devices and energy diagrams for different blocking layer of DTCTB:C60 based OSC.

(a) (b)

44

(c) (d)

(e) (f)

Fig. 3-14 J-V performances from A-18 to A-25 under (a) mCP inserted dark condition and (b) 1-sun solar illuminations, (c) NPB inserted under dark condition and (d) 1-sun solar illuminations and (e) DTDTB inserted under dark condition and (f) 1-sun solar illuminations.

Table. 3-12 Devices performances of for different blocking layer of DTCTB:C60 based OSC.

45

(a) (b)

(c) (d)

(e) (f)

46

(g) (h)

Fig. 3-15(a) EQE, (b) IQE and (c) absorption spectrum mCP inserted OSC and (d) EQE, (e) IQE and (f) absorption spectrum NPB inserted OSC and (g) EQE, (h) IQE and (i) absorption spectrum mCP inserted OSC and

3.3.3 Comparison between PMHJ and BHJ of DTCPB: C

₆₀

based OSC

Table. 3-13 Device configurations for different relative ratio between mixing transporting layer from B-1 to B-7 of DTCPB based OSC. The unit is nm.

Device MoO₃ DTCPB:C₆₀ C60 BCP Al

In this section, we introduced the second compound under single cyano groups modification. Thiophene were replaced by phenylene can gives a lower lying HOMO but remained a similar LUMO value, which resulted in a weaker absorption ability. At

47

first, we varied the ratio between mixing layer and transporting layer with a fixed thickness 60 nm with mixing ratio of 1:1.6. Table. 3-12 shows the devices configurations for tuning the devices ratio and the devices performances were also present in Table. 3-13. The J-V performances for devices from B-1 to B-7 under dark condition and illuminations were shown in Fig. 3-16. One can see that OSC with BHJ structure (B-7) exhibited highest efficiency.

(a) (b)

Fig. 3-16 J-V performances of devices under (a) dark condition and (b) 1-sun solar illuminations from B-1 to B-7.

(a) (b)

48

Fig. 3-17 (a) EQE, (b) IQE and (c) absorption spectrum of devices from B-1 to B-7.

Table. 3-14 Performances of device from B-1 to B-7 with various thickness of mixing layer under 1-sun solar illumination.

Name V_OC

3.3.4 Optimization of mixing ratio and thickness of active layer for DTCPB

3.3.4.1 C

₆₀

based OSC

In this section, we varied the mixing ratio and the thickness of the active

49

layer. The optimized values are DTCPB:C₆₀= 1: 2.2 with thickness of 90 nm in B-14, as shown below.

Table. 3-15 Device configurations for different thickness and mixing ratio of active layer for devices B-10 to B-15 of DTCPB: C₆₀ based OSC. The unit is nm.

Device MoO₃ DTCPB:C₆₀ C₆₀ BCP Al

B-7

20

1:1.6 (Mixing ratio), 70 0

7 100

B-10 1:1.6 (Mixing ratio), 80 0

B-11 1:1.6 (Mixing ratio), 90 0

B-12 1:1.6 (Mixing ratio), 100 0

B-13 1:1.4 (Mixing ratio), 90 0

B-14 1:2.2 (Mixing ratio), 90 0

B-15 1:2.6 (Mixing ratio), 90 0

(a) (b)

50

(c) (d)

Fig. 3-18 J-V performances of devices for B-7, B-10 to B-15 with different thickness under (a) and (c) dark condition and (b) and (d) 1-sun solar illuminations.

Table. 3-16 Performance of device from B-7 to B-15 with various ratio between mixing and transporting layers under 1-sun solar illumination

Name VOC

51

(a) (b)

(c) (d)

(e) (f)

Fig. 3-19 (a) and (d) EQE, (b) and (e) IQE and (c) and (f) absorption spectrum of devices in this section.

52

3.3.4.2 C

₇₀

based OSC

In this section, we optimize the DTCTB: C70 by varying the mixing ratio and thickness. The optimized condition is DTCPB: C₇₀ = 1: 2.6 with the thickness of 70 nm, as shown below.

Table. 3-17 Device configurations of DTCPB: C70 based OSC from B-16 to B-20.

The unit is nm.

Device MoO₃ DTCPB:C₇₀ BCP Al

B-16

20

1:2.2 (Mixing ratio), 60

7 100

B-17 1:2.6 (Mixing ratio), 60

B-18 1:3.0 (Mixing ratio), 60

B-19 1:2.6 (Mixing ratio), 70

B-20 1:2.6 (Mixing ratio), 80

(a) (b)

53

Fig. 3-20 J-V performances of devices from B-16 to B-20 of different mixing ratio under (a) dark condition and (b) 1-sun solar illuminations and different thickness of active layer under (c) dark condition and (d) 1-sun solar illuminations.

Table. 3-18 Performance of devices from B-16 to B-20 with various mixing ratio and thickness of active layer under 1-sun solar illumination.

Name V_OC

54

(a) (b)

(c) (d)

5

(e) (f)

Fig. 3-21 (a) EQE, (b) IQE and (c) absorption spectrum of devices with various mixing ratio of mixing layers and (d) EQE, (e) IQE and (e) absorption spectrum of devices with different thickness of active layers for C70 based OSC.

55

3.3.4.3 Insertion of blocking layer for DTCPB: C

₆₀

based OSC

In this section, we tried to insert mCP layer between MoO3 and mixing layer to prevent possible exciton quenching. However, the insertion of blocking layer resulted in higher R_S, and little enhancement (if any) on J_SC, which resulted in worse PCE.

Table. 3-19 Device configurations of DTCPB based OSC for different thickness of blocking layer from B-5, B-8 to B-9. The unit is nm.

MoO3 mCP DTCPB:C60 C60 BCP Al

B-5

20

0

1:1.6 (Mixing ratio), 60 10 7 100

B-8 1

B-9 3

(a) (b)

Fig. 3-22 J-V performances of devices from B-5, B-8 to B-9 under (a) dark condition and (b) 1-sun solar illuminations

Table. 3-20 Performances of device from B-5, B-8 to B-9 with various thickness

56

of blocking layer under 1-sun solar illumination Name V_OC

Fig. 3-23 (a) EQE, (b) IQE and (c) absorption spectrum of devices from B-5, B-8 to B-9 with various thickness of blocking layers.

3.3.5 Comparison between PMHJ and BHJ for DTCPBO/ C

₆₀

based OSC

In this section, we compared the PMHJ and BHJ structures in DTCPBO based

57

OSC. It was found that BHJ device exhibited higher PCE, as shown below.

Table. 3-21 Device configurations for different relative ratio between mixing transporting layer from C-1 to C-2 of DTCPBO based OSC. The unit is nm.

Device MoO3 DTCPBO:C60 C60 BCP Al

C-1

20

1:1.6 (Mixing ratio), 50 10

7 100

C-2 1:1.6 (Mixing ratio), 60 0

(a) (b)

(c)

Fig. 3-24 J-V performances of devices from C-1 to C-2 as (a) linear, (b) logarithm plots under dark condition and (c) 1-sun solar illuminations.

58

Table. 3-22 Performance of device from C-1 to C-2 with various relative ratio between mixing and transport layers under 1-sun solar illumination

Name VOC

Fig. 3-25 (a) EQE, (b) IQE and (c) absorption spectrum of devices from C-1 to C-2 with various relative ratio between mixing and transport layers under 1-sun solar illumination

3.3.6 Optimization of mixing ratio and thickness of active layer

59

for DTCPBO

3.3.6.1 C

60

based OSC

In this section, we varied the mixing ratio and the thickness of the active layer.

The optimized values are DTCPBO:C60= 1: 2.2 with thickness of 80 nm in C-7, as shown below.

Table. 3-23 Device configurations of DTCPBO, C₆₀ based OSC for different mixing ratio from C-2 to C-8. The unit is nm.

Device MoO3 DTCPBO:C60 BCP Al

C-2

20

1:1.6 (Mixing ratio), 60 nm

7 100

C-3 1:1.8 (Mixing ratio), 60 nm C-4 1:2.2 (Mixing ratio), 60 nm C-5 1:2.6 (Mixing ratio), 60 nm

C-6 1:2.2 (Mixing ratio), 70 nm

C-7 1:2.2 (Mixing ratio), 80 nm

C-8 1:2.2 (Mixing ratio), 90 nm

(a) (b)

60

(c) (d)

Fig. 3-26 J-V performances of devices for (a) different mixing ratio under dark condition, (b) 1-sun solar illuminations and (c) different thicknesses of active layer under dark condition, (d) 1-sun solar illuminations.

Table. 3-24 Performances of devices with different mixing ratio and different thicknesses of active layer.

61

(a) (b)

(c) (d)

Fig. 3-27 (a) EQE, (b) IQE and (c) absorption spectrum of devices with various mixing ratio of mixing layers and (d) EQE with different thickness of active layers for C₆₀ based OSC.

3.3.6.2 C

70

based OSC

In this section, we varied the mixing ratio and the thickness of the active layer.

The optimized values are DTCPBO: C70= 1: 2.6 with thickness of 70 nm in C-12, as shown below.

Table. 3-25 Device configurations of DTCPBO based OSC with different mixing ratio and thickness. The unit is nm.

Device MoO3 DTCPBO:C70 BCP Al

62

C-9

20

1:2.2 (Mixing ratio), 60 nm

7 100

C-10 1:2.6 (Mixing ratio), 60 nm C-11 1:3.0 (Mixing ratio) ,60 nm C-12 1:2.6 (Mixing ratio), 70 nm C-13 1:2.6 (Mixing ratio), 80 nm C-14 1:2.6 (Mixing ratio), 90 nm

(a) (b)

(c) (d)

63

(e)

Fig. 3-28 J-V performances of devices under various ratio for (a) dark condition and (b) 1-sun solar illuminations (c) dark with logarithms plot and various thickness for (d) dark condition and (e) 1-sun solar illuminations

Table. 3-26 Performance of devices from C-9 to C-14 with various mixing ratio and thickness under 1-sun solar illumination.

Name V_OC

64

(a) (b)

(c) (d)

(e) (f)

Fig. 3-29 (a) EQE, (b) IQE and (c) absorption spectrum of devices with various mixing ratio of mixing layers and (d) EQE, (e) IQE and (e) absorption spectrum of devices with different thickness of active layers for C70 based OSC.

65

3.3.7 Optimization of mixing ratio and thickness of active layer for DTCTBO

3.3.7.1 C

₆₀

based OSC

In the last section, we introduced DTCTBO molecule, a cyano terminal substituent with BO central bridging, thiophene electron-withdrawing modified, as electron donor under C₆₀ based OSC. For energy alignment and optical characteristic, HOMO value is lower than DTCPBO but the absorption is strongest and most red-shift within these four compounds. We varied the mixing ratio and the thickness of the active layer. The optimized values are DTCTBO:C60= 1: 2.2 with thickness of 80 nm in D-5, as shown below.

Table. 3-27 Device configurations of DTCTBO, C₆₀ based OSC for different mixing ratio and thickness of mixing layer from D-1 to D-6. The unit served as nm.

Device MoO3 DTCTBO:C60 BCP Al

D-1

20

1:1.8 (Mixing ratio), 60 nm

7 100

66

(a) (b)

(c) (d)

Fig. 3-30 J-V performance of devices from D-1 to D-6 under various ratio for (a) dark condition and (b) 1-sun solar illumination and under different thickness for (c) dark condition and (d) 1-sun solar illumination.

Table. 3-28 Performances of devices with various mixing ratio and thickness of active layer under 1-sun solar illumination.

Name VOC

67

D-4 0.84 6.87 51.07 2.94 0.60 14.35 D-5 0.84 7.56 49.48 3.14 0.58 14.61 D-6 0.84 7.68 45.05 2.92 0.42 15.85

(a) (b)

(c) (d)

(e) (f)

68

Fig. 3-31 (a) EQE, (b) IQE and (c) absorption spectrum with various mixing ratio and (d) EQE, (e) IQE and (f) absorption spectrum for different thickness.

3.3.7.2 C

70

based OSC

In this section, we varied the mixing ratio and the thickness of the active layer.

The optimized values are DTCTBO:C70= 1: 2.6 with thickness of 60 nm in D-8, as shown below.

Table. 3-29 Device configurations of DTCTBO, C₇₀ based OSC for different mixing ratio and thickness from D-7 to D-11. The unit is nm.

Device MoO3 DTCTBO:C70 BCP Al

D-7

20

1:2.2 (Mixing ratio), 60 nm

7 100

D-8 1:2.6 (Mixing ratio), 60 nm D-9 1:3.0 (Mixing ratio) , 60 nm D-10 1:2.6 (Mixing ratio), 70 nm D-11 1:2.6 (Mixing ratio), 80 nm

(a) (b)

69

(c) (d)

Fig. 3-32 J-V performances of devices to with different mixing ratio under (a) dark condition and (b) 1-sun solar illuminations, and various thickness under (c) dark condition and (d) 1-sun solar illuminations

Table. 3-30 Performances of devices from D-7 to D-11 with various mixing ratio and thickness under 1-sun solar illumination.

Name V_OC

70

(c) (d)

(e) (f)

Fig. 3-33 (a) EQE, (b) IQE and (c) absorption spectrum with various mixing ratio and (d) EQE, (e) IQE and (f) absorption spectrum for different thickness.

3.4 Comparison of optimized device structures among four single cyano groups electron donor materials

Here, we summarized four single-cyano substituent molecule which served as p-type electron donor mentioned in the above sections in Table. 3-30 and Fig. 3-34.

The optimized PCE value was obtained with DTCPB:C₇₀ -based OSC, as shown below.

71

Table. 3-31 Device configurations of dye for C₆₀ and C₇₀ based OSC for fine-tune mixing ratio and thickness. The unit served as nm.

Table. 3-31 Device configurations of dye for C₆₀ and C₇₀ based OSC for fine-tune mixing ratio and thickness. The unit served as nm.

在文檔中 具腈基小分子有機太陽能電池之優化與紅螢烯薄膜激子動態特性之研究 (頁 43-0)