Supplementary Information for
Interface engineering of graphene for universal
applications as both anode and cathode in organic
photovoltaics
Hyesung Park1,2, Sehoon Chang2, Matthew Smith2, Silvija Gradečak2, Jing Kong1*
1
Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology,
Cambridge, Massachusetts 02139, USA;
2
Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge,
Massachusetts, 02139 USA;
*
Correspondence: [email protected]
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Figure S1 | Surface morphologies of the D-HIL. (a-d) SEM micrographs of: (a) graphene; (b)
PEDOT:PEG(PC)/graphene; (c) PEDOT:PSS/graphene; (d) PEDOT:PSS/ PEDOT:PEG(PC)/graphene,
on quartz substrates. PEDOT:PSS is clearly seen to be de-wetted on the graphene surface as shown in
(c). In contrast, (b) confirms that PEDOT:PEG(PC) is completely coated on the graphene surface. (e-g)
AFM micrographs illustrating the surface morphologies of the polymeric layers on quartz substrates: (e)
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PEDOT:PEG(PC)/graphene; (f) PEDOT:PSS/PEDOT:PEG(PC)/graphene; and (g) PEDOT:PSS. The
root mean square (rms) roughness of the PEDOT:PEG(PC) layer has been reduced from 36 nm to 27 nm
upon deposition of PEDOT:PSS (rms: 1.0 nm). Both SEM and AFM images confirm that the rather
rough surface of PEDOT:PEG(PC) is smoothened by the PEDOT:PSS layer.
Figure S2 | J-V measurements of devices with graphene electrodes using either one of the HIL. (a)
When PEDOT:PEG(PC) is used as the only HIL, non-rectifying diode behavior is observed. (b)
PEDOT:PSS HIL with its matching work function at the interface still resulted in almost resistor-like
device behavior from the inadequate wetting on the graphene surface.
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Figure S3 | Characterizations of TiOx surface morphologies on graphene surface modified with
polymeric interfacial layers. (a-b) SEM micrographs of TiOx spin-coated on pristine graphene (a) and
on ITO (b). Unlike smooth coverage of TiOx film on ITO, cracks are formed on the graphene surface.
Inset in (a) shows a typical graphene surface. (c) SEM image of polymer modified graphene surface (DHIL/graphene) and (d) TiOx on the modified surface. (e-f) AFM micrographs of D-HIL (e) and TiOx on
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polymer modified graphene surface (f) all on quartz substrates. The rms roughness of each layer is 27
and 14 nm, respectively. Both SEM and AFM images show that the rough surface of polymer layers is
smoothed upon deposition of TiOx film. (g) AFM image of TiOx film spin-coated on quartz substrate
indicating its smooth surface profile. The rms roughness is less than 1.0 nm.
Figure S4 | J-V measurements of a solar cell with modified graphene electrode and without TiOx
ESL under AM 1.5G illumination at 100 mW∙cm-2. Graphene/D-HIL/C60 (40 nm)/DBP (25
nm)/MoO3 (20 nm)/Ag (100 nm).
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Figure S5 | J-V measurements of semi-transparent solar cells on graphene and ITO front
electrodes using ITO back-electrodes. (a) BHJ P3HT:PCBM solar cells. (b) BLHJ DBP/C60 solar
cells. Under AM 1.5G illumination at 100 mW∙cm-2.
Figure S6 | Schematic of flat-band energy level diagram of different types of OPV devices
considered in this work.
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Table S1. Key photovoltaic parameters for devices described in Figure 3d, indicating champion and
average values.
Anode
HTL
ITO
PEDOT:PSS
ITO
Graphene
JSC
(mA/cm2)
VOC(V)
FF(%)
PCE(%)
5.7
(5.5±0.2)
5.5
(5.2±0.2)
5.4
(5.3±0.2)
0.89
(0.89±0.01)
0.91
(0.90±0.00)
0.95
(0.92±0.04)
61.0
(61.5±0.6)
64.5
(64.7±0.2)
56.5
(58.1±2.6)
3.1
(3.0±0.1)
3.2
(3.0±0.1)
2.9
(2.7±0.1)
PEDOT:PEG(PC)/
PEDOT:PSS
PEDOT:PEG(PC)/
PEDOT:PSS
Table S2. Summary of key photovoltaic parameters of opaque devices. ‘N’, ‘I’, and ‘GR’ indicate
normal configuration, inverted configuration, and graphene, respectively.
Cathode
ESL
DBP/C60
ITO-N
ITO-I
Photoactive
material
TiOx
DBP/C60
DBP/C60
GR-N
GR-I
TiOx
DBP/C60
ITO-I
ZnO
DBP/C60
GR-I
ZnO
DBP/C60
ITO-I
ZnO
P3HT:PCBM
GR-I
ZnO
P3HT:PCBM
JSC
(mA/cm2)
VOC (V)
FF(%)
PCE(%)
5.2
(4.9±0.4)
4.5
(4.3±0.1)
5.0
(5.2±0.2)
3.9
(3.7±0.2)
3.7
(3.6±0.1)
3.6
(3.6±0.1)
10.1
(9.8±0.3)
9.2
(9.0±0.2)
0.90
(0.90±0.00)
0.84
(0.83±0.01)
0.90
(0.87±0.03)
0.86
(0.86±0.00)
0.83
(0.83±0.00)
0.73
(0.72±0.03)
0.56
(0.56±0.00)
0.55
(0.54±0.02)
62.5
(63.4±1.0)
55.5
(52.6±2.2)
61.4
(57.6±3.1)
55.6
(55.4±0.6)
61.0
(61.1±0.4)
45.7
(43.8±2.1)
54.7
(54.9±0.6)
45.1
(45.2±1.5)
2.9
(2.8±0.2)
2.1
(1.9±0.2)
2.8
(2.6±0.1)
1.9
(1.7±0.1)
1.9
(1.8±0.0)
1.2
(1.1±0.1)
3.1
(3.0±0.1)
2.3
(2.2±0.1)
Table S3. Summary of key photovoltaic parameters of inverted semi-transparent devices.
Cathode
ESL
Photoactive
material
ITO
ZnO
P3HT:PCBM
Graphene
ZnO
P3HT:PCBM
ITO
ZnO
DBP/C60
Graphene
ZnO
DBP/C60
JSC
(mA/cm2)
VOC(V)
FF(%)
PCE(%)
7.3
(7.1±0.3)
5.6
(5.6±0.3)
2.2
(2.2±0.0)
2.2
(2.1±0.1)
0.53
(0.53±0.00)
0.52
(0.53±0.01)
0.82
(0.81±0.01)
0.73
(0.73±0.00)
40.8
(39.8±3.2)
35.3
(31.3±3.5)
48.9
(48.3±1.3)
36.9
(35.9±1.2)
1.6
(1.5±0.2)
1.0
(0.9±0.1)
0.9
(0.9±0.0)
0.6
(0.5±0.0)
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