Supporting Information

for

Si-quantum-dot heterojunction solar cells with 16.2% efficiency achieved by employing doped-

graphene transparent conductive electrodes

Jong Min Kim,1* Sung Kim,1* Dong Hee Shin,1* Sang Woo Seo,1 Ha Seung Lee,1 Ju Hwan

Kim,1 Chan Wook Jang,1 Soo Seok Kang,1 Suk-Ho Choi,1† Gyea Young Kwak,2 Kyung

Joong Kim,2 Hanleem Lee,3 Hyoyoung Lee3

1 Department of Applied Physics and Institute of Natural Sciences, Kyung Hee University,

Yongin 17104, Korea.

2 Division of Industrial Metrology, Korea Research Institute of Standards and Science, P.O.

Box 102, Yuseong-gu, Daejeon, Korea.

3 Department of Chemistry, Sungkyunkwan University, Suwon 440-746, Korea.

*These authors contributed equally to this work. † To whom correspondence should be addressed. E-mail: sukho@khu.ac.kr

Tables and Figures for Supporting Information

Table S1. Photovoltaic parameters and maximum/average PCEs of undoped/AuCl3-doped graphene/SQDs solar cells without encapsulated graphene layers. Rs indicates series resistance.

nD

(mM)

Voc

(V)

Jsc

(mA/cm2)

FF

(%)

Best PCE

(%)

Average PCE

(%)

Rs

(Ω-cm2)

0 0.519 37.86 68.82 13.52 13.06 ± 0.47 3.72

5 0.508 37.05 64.39 12.13 11.36 ± 0.77 3.9

10 0.506 36.49 57.89 10.7 10.1 ± 0.69 15.44

20 0.506 35.77 52.6 9.5 9.18 ± 0.42 15.82

30 0.499 34.1 48.1 8.1 7.68 ± 0.45 16.12

Table S2. Photovoltaic parameters and maximum/average PCEs of undoped/AuCl3-doped graphene/SQDs solar cells with encapsulated graphene layers. Rs indicates series resistance.

nD

(mM)

Voc

(V)

Jsc

(mA/cm2)

FF

(%)

Best PCE

(%)

Average PCE

(%)

Rs

(Ω-cm2)

0 0.490 38.56 66.34 12.54 13.05 ± 1.13 4.34

5 0.506 39.91 68.91 13.92 13.2 ± 0.68 3.54

10 0.5 39.53 72.8 14.38 13.76 ± 0.71 3.15

20 0.498 39.12 66.9 13.03 12.53 ± 0.41 3.71

30 0.49 35.77 61.06 10.72 10.4 ± 0.42 8.65

2

Table S3. Photovoltaic parameters and maximum/average PCEs of Ag NWs-doped graphene/SQDs solar cells. Rs indicates series resistance.

nAg

(wt%)

Voc

(V)

Jsc

(mA/cm2)

FF

(%)

Best PCE

(%)

Average PCE

(%)

Rs

(Ω-cm2)

0.05 0.5133 40.01 74.35 15.27 14.37 ± 0.78 3.13

0.08 0.5124 39.77 76.97 15.69 15.03 ± 0.58 3.08

0.1 0.5120 39.60 79.80 16.17 15.41 ± 0.67 3.02

0.2 0.5118 39.19 79.62 15.97 15.11 ± 0.74 3.03

0.25 0.5110 38.81 79.11 15.69 14.89 ± 0.68 3.11

0.3 0.5108 36.87 75.35 14.17 13.69 ± 0.42 3.08

3

500 600 700 800 900 10000.0

0.2

0.4

0.6

0.8

1.0

1.2

PL in

tens

ity (a

rb.u

nits)

Wavelength (nm)

SQDs

1200 1400 1600 2600 2800

FWHM (2D) < ~40 cm-1

IG/I

2D < ~0.45

D

2D

G

Inte

nsity

(arb

. uni

ts)

Raman shift (cm-1)

Graphene

200 300 400 500 600 700 800 90050

60

70

80

90

100Graphene

Tran

smitt

ance

(%)

Wavelength (nm)

~97.70 %@550 nm

a b

c d

SQD

Si

SQDs:SiO2

Figure S1. (a) Cross-sectional high-resolution transmission electron microscopy (TEM) image of SQDs:SiO2 layer (x = 1.6). The inset shows a magnified TEM image of a single SQD. (b) PL spectrum of SQDs:SiO2 on n-Si wafer. (c) Raman spectrum of pristine graphene used in this work. The intensity ratio of G to 2D Raman bands and FWHM of 2D band are indicated. (d) Transmittance spectrum of pristine graphene.

4

Figure S2. Reflectance spectra of Al/graphene/p-SQDs/n-Si and Al/p-SQDs/n-Si solar cells.

Figure S3. (a) (b) Illustrations describing the energy band formation of a pristine graphene/p-SQDs/n-Si heterojunction solar cell. Various parameters such as band gap, electron affinity, and work function are indicated. Here, the p-SQDs are simplified like a

5

single layer even though the p-SQDs are actually alternating layers of p-SQDs and SiO2, as explained in the text.

1580 1590 1600 1610

2685

2690

2695

2700

270530 mM

20 mM10 mM5 mM

0 mM

2D fr

eque

ncy

(cm

-1)

G frequency (cm-1)

0 5 10 15 20 25 300

200400600800

100012001400

nD (mM)

She

et re

sist

ance

(/s

q)

0

20

40

60

80

100

Red

uctio

n ra

tio (%

)

b

c d

0 5 10 15 20 25 30

4.4

4.6

4.8

5.0

electron

nD (mM)

Wor

kfun

ctio

n (e

V)

hole

0

1

2

3

4

Mob

ility

(103 c

m2 V

/s)

300 450 600 750 9005060708090

100

Tran

smitta

nce

(%)

bare

Wavelength (nm)

30

0

0 10 20 3080859095

T (%

)

nD (mM)

@550 nm

a

Figure S4. (a) Transmittance spectra of AuCl3-doped graphene for various nD. The inset shows the transmittance at 550 nm as a function of nD. (b) nD-dependent correlation between Raman 2D and G band frequencies of AuCl3-doped graphene. (c) Sheet resistance and its reduction ratio of AuCl3-doped graphene as functions of nD. (d) Work function and electron/hole mobilities of AuCl3-doped graphene as functions of nD.

7 8 9 10 11 12 13 140

5

10

15

20

30 mM 20 mM

10 mM5 mM

AuCl3-doped graphene/SQDs

PCE (%)

Cou

nts

0 mM

Figure S5. Statistical deviations of the average PCE for 50 undoped and AuCl3-doped

6

graphene /p-SQDs/n-Si solar cells.

440 460 480 500 520 540 560 5800

2

4

6

8

10

12

14

PC

E (%

)

Temperature (oC)

b

-0.6 -0.3 0.0 0.3 0.6

10-7

10-6

10-5

10-4

10-3

10-2

10-1

AuCl3-doped graphene/SQDs

0 5 10 20 30

Cur

rent

den

sity

(A/c

m2 )

Voltage (V)

nD (mM)

a

Figure S6. (a) J-V curves of undoped and AuCl3-doped graphene/p-SQDs/n-Si solar cells. (b) PCE of undoped graphene/p-SQDs/n-Si solar cells as a function of annealing temperature.

a b

0 5 10 15 20 25 300

2

4

6

8

10

@550 nm

T bare-T

enca

p (%)

nD (mM)

2.3 %

0 10 20 3080859095

encap.

bare

T (%

)

nD (mM)

300 450 600 750 900

50

60

70

80

90

100

Wavelength (nm)

encapsulated

Tran

smitt

ance

(%)

0

30

Figure S7. (a) Transmittance spectra of graphene/AuCl3-doped graphene bilayers for various nD. Here, nD = 0 indicates graphene/graphene bilayers without doping. (b) Difference between transmittances of AuCl3-doped graphene without/with an encapsulation graphene layer at 550 nm. The inset shows nD-dependent transmittances of AuCl3-doped graphene without/with an encapsulation graphene layer at 550 nm.

7

9 10 11 12 13 14 150

5

10

15

20

25

30 mM

20 mM

10 mM5 mM

PCE (%)

Cou

nts

Encapsulated

0 mM

Figure S8. Statistical deviations of the average PCE for 50 undoped and AuCl3-doped graphene /p-SQDs/n-Si solar cells with encapsulation graphene layers.

0 5 10 15 20 25 30

1.8

2.0

2.2

2.4

2.6

Idea

lity

fact

or

n D (mM)

encapsulated

Figure S9. Ideality factor of graphene/AuCl3-doped graphene/p-SQDs/n-Si solar cells as a function of nD.

8

0.0 0.1 0.2 0.3

-4.4

-4.3

-4.2Ag NWs-graphene/SQDs

Wor

k fu

nctio

n (e

V)

nA (wt%)

Figure S10. Work function of Ag NWs-doped graphene as a function of nA.

400 600 800 100050

60

70

80

90

100

0.3

0

0 0 0.05 0.08 0.1 0.2 0.25 0.3

nA (wt%)

Tran

smitt

ance

(%

)

Wavelength (nm)

0.0 0.1 0.2 0.3

84889296 @550 nm

T (%

)

nA (wt%)0.0 0.1 0.2 0.3

0

200

400

600

800

1000 Ag NWs-graphene/SQDs

She

et R

esis

tanc

e (

/sq)

nA (wt%)

ba

Figure S11. (a) Sheet resistance of Ag NWs-doped graphene as a function of nA. (b) Transmittance spectra of Ag NWs-doped graphene for various nA. The inset shows the transmittance at 550 nm as a function of nA.

9

0.05 wt% 0.08 wt% 0.1 wt%

0.2 wt% 0.25 wt% 0.3 wt%

Figure S12. Scanning electron microscopy images of Ag NWs-doped graphene for various nA.

12 13 14 15 160

5

10

15

20

0.30.25 0.2

0.1

0.08

0.05

nA (wt%)

PCE (%)

Cou

nts

Ag NWs-graphene

0

Figure S13. Statistical deviations of the average PCE for 50 Ag NWs-doped graphene/p-SQDs/n-Si solar cells.

10

Figure S14. Long-term stabilities of the solar cells with pristine-, AuCl3-doped-, encapsulated- AuCl3-doped-, and Ag-NWs-doped-graphene TCEs

11