JOUL, Volume 4

Supplemental Information

Fine-Tuning Energy Levels via Asymmetric

End Groups Enables Polymer

Solar Cells with Efficiencies over 17%

Zhenghui Luo, Ruijie Ma, Tao Liu, Jianwei Yu, Yiqun Xiao, Rui Sun, Guanshui Xie, JunYuan, Yuzhong Chen, Kai Chen, Gaoda Chai, Huiliang Sun, Jie Min, JianZhang, Yingping Zou, Chuluo Yang, Xinhui Lu, Feng Gao, and He Yan

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Supporting Information

Fine-tuning Energy Levels via Asymmetric End Groups Enables Polymer

Solar Cells with Efficiencies over 17%

Zhenghui Luo,1,2,10 Ruijie Ma,1,2,10 Tao Liu, 1,2,10* Jianwei Yu,3 Yiqun Xiao,4 Rui Sun,5

Guanshui Xie,6 Jun Yuan,7 Yuzhong Chen,1,2 Kai Chen,1,2 Gaoda Chai,1,2 Huiliang Sun,1

Jie Min,5 Jian Zhang,6 Yingping Zou,7 Chuluo Yang,8 Xinhui Lu,4,* Feng Gao,3 He Yan,

1,2,9,11*

1Hong Kong University of Science and Technology-Shenzhen Research Institute, No. 9

Yuexing first RD, Hi-tech Park, Nanshan, Shenzhen 518057, P. R. China. 2Department of Chemistry and Hong Kong Branch of Chinese National Engineering

Research Center for Tissue Restoration & Reconstruction, Hong Kong University of

Science and Technology (HKUST), Clear Water Bay, Kowloon, Hong Kong, China. 3Department of Physics, Chemistry and Biology (IFM), Linköping University,

Linköping SE-58183, Sweden 4Department of Physics, Chinese University of Hong Kong, New Territories, Hong Kong,

China. 5The Institute for Advanced Studies, Wuhan University, Wuhan 430072, China. 6School of Materials Science and engineering, Guangxi Key Laboratory of Information

Materials, Guilin University of Electronic Technology, 1st Jinji Road, Guilin, 541004, P.

R. China. 7College of Chemistry and Chemical Engineering, Central South University, Changsha

410083, P. R. China

8Shenzhen Key Laboratory of Polymer Science and Technology, College of Materials

Science and Engineering, Shenzhen University, Shenzhen 518060, China. 9State Key Laboratory of Luminescent Materials and Devices, South China University of

Technology, Guangzhou 510640, China. 10These authors contributed equally. 11Lead Contact

*Correspondence: liutaozhx@ust.hk (T.L.), xinhui.lu@cuhk.edu.hk (X.L), hyan@ust.hk

(H.Y.)

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Materials and Measurements

All solvents and reagents were used as received from commercial sources and used

without further purification unless otherwise specified. 1H NMR (400 MHz) and 13C NMR

(100 MHz) spectra were measured on a MERCURYVX300 spectrometers. Mass spectra

were recorded on a Shimadzu spectrometer. UV-vis-NIR absorption spectra were recorded

on a Shimadzu UV-2700 recording spectrophotometer. Cyclic voltammetry (CV)

measurements were carried out on a CHI voltammetric analyzer at room temperature.

Tetrabutylammonium hexafluorophosphate (n-Bu4NPF6, 0.1 M) was used as the

supporting electrolyte. The conventional three-electrode configuration consists of a

platinum working electrode with a 2 mm diameter, a platinum wire counter electrode, and

a Ag/AgCl wire reference electrode. Cyclic voltammograms were obtained at a scan rate

of 100 mV/s. PL spectra were measured with a Shimadzu RF-5301PC fluorescence

spectrophotometer. The film morphology was measured using an atomic force microscope

(AFM, Bruker-ICON2-SYS) using the tapping mode. The RMS values of the surface AFM

images are averaged based on five times testing on different areas for each sample. DFT

calculations were performed by using Gaussian at the B3LYP-D3(BJ)/def2-SVP level, and

the long alkyl chain was simplified as methyl.

Device fabrication and characterization

Solar cells were fabricated in a conventional device configuration of

ITO/PEDOT:PSS/active layers/PNDIT-F3N/Ag. The ITO substrates were first scrubbed

by detergent and then sonicated with deionized water, acetone and isopropanol

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subsequently, and dried overnight in an oven. The glass substrates were treated by UV-

Ozone for 30 min before use. PEDOT:PSS (Heraeus Clevios P VP AI 4083) was spin-cast

onto the ITO substrates at 4000 rpm for 30 s, and then dried at 150 °C for 15 min in air.

The PM6 (Mn =40.8 KDa with PDI of 2.04): acceptor blends (1:1.2 weight ratio) were

dissolved in chloroform (the total concentration of blend solutions was 15 mg mL-1 for all

blends), 0.5% (vol%) 1-chloronaphthalene was utilized as the solvent additive, and stirred

overnight in a nitrogen-filled glove box. The blend solution was spin-cast at 3000 rpm for

30 s. A thin PNDIT-F3N layer was coated on the active layer, followed by the deposition

of Ag (100 nm) (evaporated under 5×10-5 Pa through a shadow mask). The optimal active

layer thickness measured by a Bruker Dektak XT stylus profilometer was about 105 nm.

The current density-voltage (J-V) curves of all encapsulated devices were measured using

a Keithley 2400 Source Meter in air under AM 1.5G (100 mW cm-2) using a Newport solar

simulator. The light intensity was calibrated using a standard Si diode (with KG5 filter,

purchased from PV Measurement to bring spectral mismatch to unity). Optical microscope

(Olympus BX51) was used to define the device area (5.9 mm²). EQEs were measured using

an Enlitech QE-S EQE system equipped with a standard Si diode. Monochromatic light

was generated from a Newport 300W lamp source.

To confirm the reliability of the champion PCE of the PM6:BTP-2F-ThCl-based device,

we sent our acceptor material of BTP-2F-ThCl to two different research groups to

reproduce the result, namely, Min Jie’s group and Zhang jian’s group. The optimal J-V

curves of PSCs and corresponding IPCE spectra are exhibited in Figure S9. In Min's group,

S4

they used the same device conditions as our group, and the PM6:BTP-2F-ThCl-based

device yields a PCE of 16.8%, with a VOC of 0.862 V, a JSC of 25.4 mA/cm2 along with a

FF of 0.768. However, in Zhang’s group, even if they employed PDINO instead of PNDIT-

F3N as the electron transport layer, the PM6:BTP-2F-ThCl-based device yields a PCE of

16.9%, with VOC of 0.883 V, a JSC of 25.3 mA/cm2 along with a FF of 0.755. These results

indicate the reliability of champion PCE of the PM6:BTP-2F-ThCl-based device.

Mobility Measurements

Hole and electron mobility were measured using the space charge limited current (SCLC)

method. Device structures are ITO/MoOx/active layer/MoOx/Ag for hole-only devices and

ITO/ZnO/active layer/PNDIT-F3N/Ag for electron-only devices. The SCLC mobilities

were calculated by MOTT-Gurney equation: J = 9ε0εrμV2/8L3. Where J is the current

density, εr is the relative dieletiric constant of active layer material usually 2-4 for organic

semiconductor, herein we use a relative dielectric constant of 3, ε0 is the permittivity of

empty space, µ is the mobility of hole or electron and L is the thickness of the active layer,

V is the internal voltage in the device, and V = VApplied – VBuilt-in (in the hole-only and the

electron-only devices, the Vbi values are 0.2 V and 0 V respectively), where VApplied is the

voltage applied to the device, and VBuilt-in is the built-in voltage resulting from the relative

work function difference between the two electrodes.

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GIWAXS measurement

GIWAXS measurement were carried out with a Xeuss 2.0 SAXS/WAXS laboratory

beamline using a Cu X-ray source (8.05 keV, 1.54 Å) and a Pilatus3R 300K detector. The

incidence angle is 0.2°. The samples for GIWAXS measurements are fabricated on silicon

substrates using the same recipe for the devices.

Scheme S1. Synthesis of BTP-2F-ThCl and IT-2FCl.

Synthesis of BTP-2F-ThCl:

BTP-4F-CHO (200 mg, 0.195 mmol), compound 2 (49.3 mg, 0.2145 mmol), compound 3

(50.2 mg, 0.2145 mmol), chloroform (20 mL), and pyridine (1 mL) were added to a two-

necked round-bottomed flask. The mixture was deoxygenated with nitrogen for 30 min and

then refluxed for 24 h. After cooling to room temperature, the mixture was poured into

methanol (200 mL) and filtered. The residue was purified by column chromatography on

silica gel using petroleum ether/dichloromethane (1:1) as eluent, yielding a dark blue solid

(113 mg, 40%). 1H NMR (CDCl3, 400 MHz): δ [ppm]: 9.07 (s, 1H), 8.97 (s, 1H), 8.51–

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8.47 (m, 1H), 8.10 (s, 1H), 7.72 (t, J = 7.3 Hz, 1H), 4.81 (s, 4H), 3.18 (s, 4H), 2.18 (s, 2H),

1.84 (d, J = 6.4 Hz, 4H), 1.47 (s, 4H), 1.37–0.96 (m, 44H), 0.92–0.65 (m, 18H). 13C NMR

(100 MHz, CDCl3): δ [ppm]: 186.14, 158.67, 153.86, 147.39, 145.24, 141.45, 138.03,

137.82, 136.54, 136.00, 135.15, 133.90, 133.38, 133.23, 131.59, 130.45, 126.50, 125.20,

119.90, 114.83), 113.70, 112.40, 77.29, 77.03, 76.71, 66.32, 55.72, 40.39, 31.91, 31.19,

30.12, 29.24, 27.61, 23.20, 22.89, 22.69, 14.12, 13.78, 10.48, 10.11. MS (MALDI-TOF)

m/z: [M+H]+ calcd. for (C80H85ClF2N8O2S6): 1454.4776; Found: 1454.4776.

Synthesis of IT-2FCl:

IT-CHO (200 mg, 0.196 mmol), compound 2 (49.6 mg, 0.2156 mmol), compound 3 (50.5

mg, 0.2156 mmol), chloroform (30 mL), and pyridine (1 mL) were added to a two-necked

round-bottomed flask. The mixture was deoxygenated with nitrogen for 30 min and then

refluxed for 24 h. After cooling to room temperature, the mixture was poured into methanol

(200 mL) and filtered. The residue was purified by column chromatography on silica gel

using petroleum ether/dichloromethane (1:2) as eluent, yielding a dark blue solid (88.3 mg,

30%). 1H NMR (CDCl3, 400 MHz): δ [ppm]: 8.85 (s, 1H), 8.78 (s, 1H), 8.53 (dd, J = 7.5

Hz, 1H), 8.22 (s, 2H), 8.12 (s, 1H), 7.75-7.67 (m, 3H), 7.22 (d, J = 7.9 Hz, 8H), 7.15 (d, J

= 7.8 Hz, 8H), 2.58 (t, J = 7.6 Hz, 8H), 1.65-1.57 (m, 8H), 1.35-1.20 (m, 24H), 0.92-0.82

(m, 12H). 13C NMR (100 MHz, CDCl3): δ [ppm]: 185.12, 179.19, 157.55, 155.26, 154.19,

153.30, 153.03, 147.59, 147.38, 146.87, 143.42, 141.99, 140.69, 139.15, 138.83, 138.14,

137.78, 136.88, 136.42, 135.33, 131.24, 128.29, 127.59, 127.23, 124.89, 121.14, 118.09,

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114.46, 114.10, 113.53, 76.73, 76.41, 76.09, 67.02, 62.65, 34.98, 31.07, 30.63, 28.56, 21.96,

13.46. MS (MALDI-TOF) m/z: [M+H]+ calcd. for (C92H77ClF2N4O2S5): 1502.4307; Found:

1502.4296.

Figure S1. 1H NMR spectrum of BTP-2F-ThCl in CDCl3.

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Figure S2. 13C NMR spectrum of BTP-2F-ThCl in CDCl3.

Figure S3. MS spectrum (MALDI-TOF) of BTP-2F-ThCl.

lzh-43, MW=1458; DCTB;

m/z1400 1405 1410 1415 1420 1425 1430 1435 1440 1445 1450 1455 1460 1465 1470 1475 1480 1485 1490 1495 1500 1505 1510 1515

%

0

100

yan191107_2 4 (0.132) Cn (Cen,2, 10.00, Ar); Sb (5,20.00 ); Sm (SG, 2x3.00); Cm (4:15) TOF LD+ 4.30e31456.3555

1455.3699

1454.3820

1451.4705

1457.3326

1458.3212

1459.3008

1460.2939

1461.2612

1462.2878

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Figure S4. 1H NMR spectrum of IT-2FCl in CDCl3.

Figure S5. 13C NMR spectrum of IT-2FCl in CDCl3.

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Figure S6. MS spectrum (MALDI-TOF) of IT-2FCl.

Figure S7. The frontier molecular orbitals obtained by DFT for BTP-4F, BTP-2F-ThCl

and BTP-2ThCl.

lzh-5; MW=1502; DCTB

m/z1455 1460 1465 1470 1475 1480 1485 1490 1495 1500 1505 1510 1515 1520 1525 1530 1535 1540 1545 1550 1555

%

0

100

yan191126_1 16 (0.534) Cn (Cen,2, 10.00, Ar); Sb (5,20.00 ); Sm (SG, 2x3.00); Cm (3:17) TOF LD+ 2911504.4258

1502.4296

1499.51941479.74241459.8209 1469.6145 1489.8700

1505.4268

1506.4302

1507.4169

1508.4218

1509.4114

1551.96951514.5022 1529.23821522.4368 1535.46081548.7607

1558.1600

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Figure S8. Space-charge-limited (SCLC) J-V characteristics of neat BTP-4F, BTP-2F-

ThCl and BTP-2ThCl film under dark condition.

Figure S9. The Photovoltaic Properties: (A) J-V characteristics of the best OSCs under

the illumination of AM 1.5G, 100 mW cm−2; (B) IPCE spectra of the best devices based

on PM6:BTP-2F-ThCl.

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Figure S10. Device stability: (A) The long-term stability of PM6:BTP-4F, PM6:BTP-2F-

ThCl and PM6:BTP-2ThCl-based PSCs within 30 days packaged conventional devices

stored in air; (B) The photostability of PM6:BTP-4F, PM6:BTP-2F-ThCl and PM6:BTP-

2ThCl-based PSCs within 108 hours packaged conventional devices under LED flood

light with a power of 150W illumination.

Table S1 The parameters of exciton dissociation efficiency and charge collection

efficiency.

Active layer Jsat

(mA/cm2)

Jpha

(mA/cm2)

Jphb

(mA/cm2)

ηdiss (%) ηcoll (%)

PM6:BTP-4F 26.60 25.19 22.30 94.7 83.9

PM6:BTP-2F-

ThCl

26.70 25.38 23.06 95.0 86.3

PM6:BTP-

2ThCl

25.80 23.46 18.91 90.9 73.3

a: Under short circuit condition; b: Under the maximal power output condition

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Figure S11. J-V characteristics in dark for hole-only (A) and electron-only (B) devices

based on PM6:BTP-4F, PM6:BTP-2F-ThCl and PM6:BTP-2ThCl blends.

Table S2. The parameters of hole mobilities and electron mobilities.

Active layer μh

(10-4 cm2 V-1 s-1)

μe

(10-4 cm2 V-1 s-1)

μh/μe

PM6:BTP-4F 5.89 3.69 1.60

PM6:BTP-2F-ThCl 5.21 3.28 1.58

PM6:BTP-2ThCl 4.78 2.55 1.87

Figure S12. 2D GIWAXS patterns of PM6:BTP-4F, PM6:BTP-2F-ThCl and PM6:BTP-

2ThCl blend films.

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Figure S13. The contact angle images of neat PM6, BTP-4F, BTP-2F-ThCl and BTP-

2ThCl films.

Table S3. Contact angles of water and ethylene glycol (EG), and surface free energy, and

Flory–Huggins interaction parameters of PM6, BTP-4F, BTP-2F-ThCl, and BTP-2ThCl.

The average contact angles and standard deviations were obtained from 5 films.

Surface θwater (o) θEG (o) γ (mN/m)(a) χ [PM6, i](b)

PM6 107.1 ± 0.5 75.6 ± 0.7 27.4

BTP-4F 90.3 ± 0.4 57.3 ± 0.8 33.1 0.27

BTP-2F-ThCl 89.4 ± 0.6 69.3 ± 1.0 21.8 0.31

BTP-2ThCl 100.0 ± 0.3 66.6 ± 0.5 31.4 0.13

(a) The surface free energy (γ) calculated by Young’s equation.

(b) The Flory-Huggins interaction parameters between the donor (D) and the acceptor (A)

calculated using χ = (√γD-√γA)2.

Figure S14. GISAXS intensity profiles and best fittings along the in-plane direction.

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Table S4. Summary of parameters measured and calculated from FTPS-EQE and EL.

Device Eg

pv

(eV)

EQEEL

10-4

Eloss

(eV)

q∆VSQ

oc

(eV)

∆E1=Egap-q∆VSQ

oc

(eV)

qVrad

oc

(eV)

∆E2 =q∆Vrad.

oc

(eV)

∆E3= q∆Vnon-

rad oc

(eV)

Voccal

(eV)

BTP-4F 1.40 0.69 0.56 1.14 0.26 1.09 0.05 0.25 0.84

BTP-2F-ThCl 1.40 1.7 0.53 1.14 0.26 1.09 0.05 0.22 0.87

BTP-2ThCl 1.41 3.0 0.52 1.15 0.26 1.10 0.05 0.21 0.89