High-Efficiency Nonfullerene Polymer Solar Cell Enabling by

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High-Efficiency Nonfullerene Polymer Solar Cells Enabling by Integration of Film-Morphology Optimization, Donor Selection, and Interfacial Engineering Xin Zhang, Weiping Li, Jiannian Yao, and Chuanlang Zhan ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b03926 • Publication Date (Web): 01 Jun 2016 Downloaded from http://pubs.acs.org on June 3, 2016

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ACS Applied Materials & Interfaces

High-Efficiency Nonfullerene Polymer Solar Cells Enabling by Integration of Film-Morphology Optimization, Donor Selection, and Interfacial Engineering

Xin Zhang, Weiping Li, Jiannian Yao, and Chuanlang Zhan* Beijing National Laboratory of Molecular Science, CAS Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, P. R. China.

ACS Paragon Plus Environment

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ABSTRACT Carrier mobility is a vital factor determining the electrical performance of organic solar cells. In this paper we report that high-efficiency non-fullerene organic solar cell (NF-OSC) with a power conversion efficiency of 6.94 ± 0.27% was obtained by optimizing the hole and electron transportations via following judicious selection of polymer donor and engineering of filmmorphology and cathode interlayers: (1) a combination of solvent annealing and solvent vapor annealing optimizes the film-morphology and hence both hole and electron mobilities, leading to a trade-off of fill factor and short-circuit current density (Jsc); (2) the judicious selection of polymer donor affords a higher hole and electron mobility, giving a higher Jsc; and (3) engineering the cathode interlayer affords a higher electron mobility, which leads to a significant increase in electrical current generation and ultimately the PCE. KEYWORDS: perylene diimides, film-morphology optimization, interfacial engineering, solution-processed, nonfullerene organic solar cell. INTRODUCTION Non-fullerene organic solar cells (NF-OSCs) utilize n-type organic molecules instead of traditional fullerenes1,2 as the blend acceptor(s) and can be fabricated via easy-handling solutionprocessed methods. Because organic acceptor is, with respect to traditional fullerene one, easyaccessible via organic synthesis and easy-tunable on its optoelectronic property and aggregation behavior, much effort has been recently made on the explorations of organic acceptors. So far, there reported several kinds of efficient organic small-molecule acceptors such as twisted perylene diimides (PDIs),3-6 twisted tetraazabenzodifluoranthene diimides (BFIs),7 twisted bis(diphenylethynyl-tetraphenylaza dipyrromethene) zinc(II) complex,8 among others.9


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Otherwise, there reported several polymer acceptors, for example, those with PDI 10 or naphthalene diimide (NDI) 11 as the conjugated electron-accepting moieties. With these smallmolecules or polymers as the non-fullerene acceptor, the solar-to-electrical power conversion efficiencies of 6−7% was reported by several groups,6,11-19 and, very recently a PCE of 7.1%20 and 7.7%21 was reported from a solution-processed twisted sulfur-fused dimeric PDI and a NDIselenophene conjugated polymer acceptor, respectively. All these exciting results point out potentiality of NF-OSCs. In an NF-OSC device, both organic acceptor and organic donor are blended together as the photoactive layer to capture and convert the solar photons into mobile charges, which are then collected by the right electrodes. Absorptivity, film-morphology and organic-to-electrode interlayers play very important roles in determining solar cell’s electrical performance, among which the latter two are deeply related to the carrier transportation. Organic acceptors such as PDIs normally shown absorption in the visible region. The first consideration is to complement the visible absorption spectrum of the acceptor by selecting a low band gap donor material, and the absorption of the donor material will have an impact on the solar photons capturing ability of the blended film, affecting the solar cell performance. For example, it was observed that the solar cell electrical performance can be significantly improved as the blend donor was changed from P3HT to a low band gap polymer such as PBDTTT-C-T/PffBT4T-2DT with the PCE going from 1.3%/2.4% to 4.0%/5%.14,22,23 Again, similar phenomenon with the PCEs varying between 1% and 4.5% was observed from several polymer donors with absorption bands covering different spectral wavelength regions.24 Charge dissociation is the second consideration in selection of donor-to-acceptor combination. It is accepted that the donor-to-acceptor energy offset between the lowest unoccupied molecular orbitals (LUMO) and that between the highest occupied


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molecular orbitals (HOMO) should be larger than 0.3 eV, acting as the driving forces for efficient charge dissociation through the electron and hole transfer paths. Nevertheless, there were only several all-organic combinations as yet realized to show high performance. The third consideration is film-morphology. Optimal nanoscale and interpenetrating networks of donor-to-acceptor phase-separated domains are beneficial for charge-dissociation and carriertransportation. For an NF-OSC, morphology of acceptor phase domains is likely an important factor that limits the electrical performance of NF-OSCs. Film-processing techniques which were proven efficient for fullerene OSCs have been widely shown to work for optimizations of filmmorphology of all-organic systems. For example, it was shown that processing the blend film with high boiling-point solvents as additives can optimize the film-morphology, and/or with solvent or solvent-vapor annealing (SA or SVA) techniques can reconstruct the filmmorphology, both of which lead to formation of charge-dissociation favorable and chargetransport beneficial film-morphologies with improved electron transport.13,20 Again, it was indicated that (1) well-ordered PDI domains suffer from poor electrical coupling between the PDI domains, which leads to a decreasing electron mobility 25 and (2) phase size of acceptor domains in the phase-separated blend films could be correlated to the short-circuit current density (Jsc) in some PDI:small molecule donor systems.26 Besides, the forth consideration is to modify the organic-to-electrode interfaces, the cathode interlayers, which have been proven affective on improving the collection of electrons, and so on raising the Jsc, fill-factor (FF) and ultimately the PCE value of fullerene OSCs.27-30 In this paper, we selected three low band gap polymers, PTB7,31 PTB7-Th 32 and PBDT-TS1 33 (Figure 1a), as the donors and a previously reported PDI dimer of bis-PDI-T-EG (Figure 1a)4 as the non-fullerene small-molecule acceptor. Optimizations of film-morphology of the PTB7-Th


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blend with a combination of SA and SVA treatments optimized the hole and electron mobilities and led to a trade-off between Jsc and FF, affording a PCE of 4.96 ± 0.24%. The PCE value was improved to 5.65 ± 0.20% as the cathode interlayer was changed from Ca to PDINO 34, 35 (Figure 1a). As PBDT-TS1 was selected as the polymer donor, a PCE of 6.22 ± 0.16% and 6.94 ± 0.27% was achieved with Ca and PDINO as the cathode layer.

(a) Polymer donors C2H5

C2H5

O

S

O

S

S

S

N

O

O

N

O

O

S

n S

PTB7-Th

O

C8H17

N

O

O

N

PBDT-TS1

O

C2H5

C2H5

PDINO

0.0 300

450

600 λ / nm

750

0.0 900

-5

-5.02

-6

-3.59

-3.71

PBDT-TS1

-4

-3.39

PTB7-Th

0.5

-3

PTB7

-1

0.8

-2

1.0

Irradiance (W m

1.2

0.4

O

N O

(c) 1.5 Energy level / eV

PBDT-TS1

nm )

PTB7-Th

N

O

C4H9

Bis-PDI-T-EG

PTB7 PDI

O

O

O

O

C4H9

(b) 1.6

N

O

S

C2H5 C4H9

PTB7

N

S S

n

C4H9

O

O

O

C4H9

C4H9

F S

S

C2H5

C2H5

C2H5

C4H9

O S

S

n

O

C8H17

F

S

S

C2H5

C4H9

S

S

S S

C4H9

O

O

F

O

C2H5

C2H5

-5.17

-5.26

-3.84

PDI

C4H9

Electron transporting layer

PDI acceptor

C4H9

Abs / a.u.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


-5.64

Figure 1. (a) Molecular structures of the selected polymer donors and the non-fullerene acceptor of bis-PDI-T-EG. (b) Normalized UV-vis absorption spectra of the pure donor and acceptor film, and solar photon flux at AM1.5 conditions (black). (c) HOMO and LUMO energy levels which were obtained from ultraviolet photoelectron spectroscopy (UPS) data (Figure S1) and film absorption spectrum (Figure 1b), respectively. RESULTS AND DISSCUSSION


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Figure 1b gives the absorption spectra of the three polymers and the PDI acceptor. The absorption band red-shifted to a longer wavelength region for the polymer, going from PTB7 to PTB7-Th and PBDT-TS1, which became more complementary to the absorption of the PDI acceptor and the all-organic combination had a wider coverage of solar emission spectrum. All the three polymers had a higher-lying LUMO or HOMO energy level than the PDI acceptor (Figure 1c and Figure S1), providing driving forces for efficient dissociation of the excitons generated by the blended donor and acceptor domains. Firstly, we selected PTB7-Th as the blend donor. High boiling-point additive solvent of 1,8-diiodooctane (DIO) and post treatment following a SA/SVA process were used for film-morphology optimizations. As the as-cast photoactive layer was put in an open petri dish for 2 h (without any treatments of SA or SVA), the best cell shown four parameters as follows: Jsc = 9.17 ± 0.21 mA/cm2, Voc (open-circuit voltage) = 0.884 ± 0.008 V, FF = 0.430 ± 0.016 and the PCE = 3.47 ± 0.24% (hereafter, named as cell A, Table 1). Upon post treatment with SA in a fully covered petri dish (hereafter, named as cell B) for 30 and 45 min, the Jsc increased to 10.89 ± 0.19 and 11.29 ± 0.13 mA/cm2, respectively. The Voc was of 0.874 ± 0.006 and 0.870 ± 0.008 V and FF was of 0.453 ± 0.013 and 0.458 ± 0.017, respectively, which gave the PCE of 4.30 ± 0.25% and 4.46 ± 0.16% (Table S2). If 7.5 µL of the host processing solvent, 1,2-dichlorobenzene (o-DCB), was pre-added into a fully covered petri dish prior to the deposition of active layer (hereafter, named as cell C), the best cell was obtained after 15 min of SVA with the PCE = 4.60 ± 0.29%, Jsc = 10.03 ± 0.15 mA/cm2, Voc = 0.872 ± 0.009 V, and FF = 0.528 ± 0.014. SVA for a longer time led to a slight increase in FF, while an obvious decrease in Jsc (Table S2). Comparisons of the SA and SVA results indicated that SA could gave a higher Jsc, while SVA could be


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helpful for a higher FF. Therefore, we combined SA and SVA by firstly treating the ascast solar cell blend in a fully covered petri dish, for example, for 30 min (SA) and then the blend was quickly moved into another fully covered petri dish with 7.5 µL of o-DCB inside, for example, for another 15 min (SVA) (hereafter, named as cell B+C). The optimization details were shown in Table S2. As a result, both the higher Jsc and FF values were maintained, giving the PCE value of 4.96 ± 0.24% with Jsc = 10.89 ± 0.22 mA/cm2, Voc = 0.876 ± 0.009 V, and FF = 0.523 ± 0.013 (Table 1). Figures 2a and 2b are the current density − voltage (J − V) characteristics and external quantum efficiency (EQE) responses of the best solar cells of B, C and B+C, respectively, and Table 1 collects the average values of the four cell parameters obtained under conditions of A, B, C and B+C, respectively. The current integrated from the EQE curves were 10.53, 10.37, and 8.69 mA/cm2 for the best solar cells of B, B+C and C, respectively. Table 1. Electrical parameters of the solar cells obtained with PTB7-Th as the donor and under conditions A, B, C and B+C, respectively

Polymer

Condition

Time [min]

Voc [V]a

Jsc [mA cm-2]a

FFa

PCE [%]a

µeb/µhc [cm2 V-1 s-1]

PTB7-Th

A

120

0.884 ± 0.008

9.17 ± 0.21

0.430 ± 0.016

3.47 ± 0.24 (3.72)

/

B

45+0

0.870 ± 0.008

11.29 ± 0.13

0.458 ± 0.017

4.46 ± 0.16 (4.64)

8.63/17.2×10-5

B+C

30+15

0.876 ± 0.009

10.89 ± 0.22

0.523 ± 0.013

4.96 ± 0.24 (5.23)

9.01/12.4×10-5

C

0+45

0.877 ± 0.006

9.12 ± 0.23

0.549 ± 0.011

4.36 ± 0.27 (4.66)

4.73/6.89×10-5

a

Average values from 10 devices with the best PCE shown in brackets. bElectron mobilities were measured with devices of ITO/TIPD/active layer/Ca/Al. cHole mobilities were measured with devices of ITO/PEDOT:PSS/active layer/Au.


7


-6

30 20 Cell B Cell B + C Cell C

-9 10

-12

V/V

Cell B Cell B + C Cell C

1000

40

-3

-1.5 -1.0 -0.5 0.0

30000

1500

50

0.5

1.0

Intensity (counts)

0

Cell B Cell B + C Cell C

EQE / %

3

(c)

(b) 60

0 300

25000 20000

Out-of-Plane

15000

500

10000

0 In-Plane

-500 400

500

600

700

800

900

λ / nm

5000

Intensity (counts)

(a) 6

J / mAcm-2

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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0

5

10

15 2θ /

20

25

30

o

Figure 2. Experimental J-V characteristics (a) and EQE responses (b) of the optimal solar cells with PTB7-Th as the donor. The out-of-plane and in-plane 1D-GIXRD data (c) of the pure PTB7-Th film (green) and the solar cell blends obtained under conditions B, B+C and C, respectively. Both hole and electron mobilities were estimated with space-charge-limited-current (SCLC) method (Supporting information and Figure S2) and Table 1 collects the values. The hole mobility decreased as the condition went from B to B+C and C, e.g. from SA only to SA+SVA and SVA only, which was consistent with the “dissolution” of white domains with the phase size decreasing from 250 to 30 and 25 nm (Figure S3a-c). We noted that the white phases could be contributed mainly from the polymer donor, while the black phases from the PDI acceptor, according to our previously reported paper.13 The one-dimensional (1D) and two-dimensional (2D) grazing-incidence X-ray diffraction (GIXRD) 36 data (Figure 2c and S4) indicated close (010) diffraction patterns for all three blends in both the out-of-plane and in-plane directions. The more intense (010) diffraction along the out-of-plane than that along the in-plane indicated the preferable face-on orientation. As demonstrated in Figure 2c by the green lines, the (100) diffraction of the pure PTB7-Th film appeared as a broad band around 2θ = 3.8° and 4.4° along the out-of-plane direction and as a sharp band around 3.7° along the in-plane direction. As


8

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blended with PDI acceptor, intense (100) diffractions were observed at 2θ = 4.0° along the outof-plane and at 3.5° along the in-plane, each of which positioned at a smaller 2θ value than that from the pure polymer film and were assumed to be mainly contributed from the acceptor. The different positions of the (100) diffractions at the out-of-plane and at the in-plane can be associated with the packing patterns of dimeric PDI molecules, for example, along the bay-tobay and the nitrogen-to-nitrogen directions of perylene, respectively. The (100) diffraction intensity slightly decreased in both the out-of-plane and in-plane directions as the condition went from B to B+C and C. The electron mobilities were close to each other for the three cells with the estimated value slightly decreasing from cell B to B+C and C. The sum of the hole and electron mobility values decreased by the order of B > B+C > C, which agreed well with the decreased trend of the Jsc. Again the electron-to-hole mobility became more and more balanced, contributing to the increase of the FF. The FF value is again related to the recombination losses of the mobile charges. Recombination losses of devices were reflected from incident light-power (P0) dependences of Jsc and Voc. The relationship between Jsc and light intensity follows the relation, Jsc ∝ Pα.37 For the three cells, the α values estimated from the plots of Jsc versus P0 (Figure S5a) were all close to each other, typically, 0.95. At open-circuit, recombination mechanism is reflected by the relation, Voc ∝ nkT/qln(P), where k, T and q are the Boltzmann constant, the temperature in Kelvin and the elementary charge, respectively.37 The n values estimated from the plots of Voc versus P0 (Figure S5b) were close for cells B+C and C (1.08 vs. 1.09 kT/q), while that value from cell B was more deviated from one (1.31 kT/q), indicating stronger loss involved, which is again consistent with the lower FF value for cell B.


9


(a) 2

(b) 70

0

-4

50 EQE / %

J / mAcm-2

60

PTB7 PTB7-Th PBDT-TS1

-2

-6 -8

40 30

-10

20

-12

10

-14 -0.2

0.0

0.2

0.4 V/V

0.6

0.8

(d)

0.4

0 300

1.0

400

500

600

700

800

900

λ / nm

(c)

(e)

Out-of-plane

In-plane

5000

1000

PTB7+PDI

0.3 0.2 PTB7 PTB7-Th PBDT-TS1

0.1

PTB7

Intensity (a.u.)

Intensity (a.u.)

PTB7+PDI

Abs / 100 nm

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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PTB7 PTB7-Th+PDI PTB7-Th

PTB7-Th+PDI PTB7-Th

PBDT-TS1+PDI PBDT-TS1

PBDT-TS1+PDI PBDT-TS1

0.0 400

600

800

5

10

λ / nm

15 2θ /

20

25

30

o

5

10

15 2θ /

20

25

30

o

Figure 3. Experimental J-V characteristics (a) and EQE response (b) of the optimal PTB7, PTB7-Th, and PBDT-TS1 based solar cells, respectively. The absorption spectra (c) and the outof-plane (d) and in-plane (e) 1D GIXRD data of the corresponding solar cell blends. Table 2. Electrical parameters of the solar cells obtained with PTB7, PTB7-Th, and PBDTTS1 as the donor materials, respectively

Cathode

Voc [V]a

PTB7

PDINO/Al

0.840 ± 0.006

8.46 ± 0.19

0.552 ± 0.017

3.88 ± 0.21 (4.10)

2.75c /5.66×10-5

PTB7-Th

PDINO/Al

0.876 ± 0.007

11.14 ± 0.21

0.583 ± 0.012

5.65 ± 0.20 (5.87)

10.3c /12.1×10-5

PBDT-TS1

PDINO/Al

0.887 ± 0.005

13.23 ± 0.19

0.594 ± 0.019

6.94 ± 0.27 (7.24)

18.7c /16.3×10-5

PBDT-TS1

Ca/Al

0.885 ± 0.008

12.41 ± 0.22

0.569 ± 0.018

6.22 ± 0.16 (6.42)

11.6d/16.3×10-5

PBDT-TS1

Al

0.874 ± 0.007

11.66 ± 0.23

0.418 ± 0.024

4.23 ± 0.17 (4.41)

9.81e/16.3×10-5

PBDT-TS1

MeOH/Ca/Al

0.885 ± 0.006

11.85 ± 0.18

0.551 ± 0.017

5.75 ± 0.22 (5.99)

/

PBDT-TS1

MeOH/Al

0.865 ± 0.005

11.25 ± 0.26

0.437 ± 0.026

4.22 ± 0.16 (4.39)

/

Polymer

Jsc [mA cm-2]a

FFa

a

PCE [%]a

µe/µhb [cm2 V-1 s-1]

b

Average values from 10 devices with the best PCE shown in brackets. Hole mobilities were measured with devices of ITO/PEDOT:PSS/active layer/Au. c, d, eElectron mobilities were


10

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measured with devices of ITO/TIPD/active layer/PDINO/Al, ITO/TIPD/active layer/Ca/Al, and ITO/TIPD/active layer/Al, respectively. By utilizing PDINO to replace the Ca layer, we again fabricated the solar cells under the condition B+C, the optimal solar cell shown an improved PCE (5.65 ± 0.20% vs. 4.96 ± 0.24%) with an increasing FF (0.583 ± 0.012 vs. 0.523 ± 0.013), and an close Jsc and Voc (Tables 2 and 1). A change of the polymer donor from PTB7-Th to a lower band gap polymer of PBDT-TS1 produced a higher PCE of 6.94 ± 0.27%, while changing to a wider band gap polymer of PTB7 led to a lower PCE of 3.88 ± 0.21% (Table 2). The optimization details were shown in Table S3. Figure 3a and b give the J−V characteristics and EQE responses of the best solar cells from the PTB7, PTB7-Th and PBDT-TS1 blends, respectively. The current integrated from the EQE curves were 8.17, 10.75, and 12.59 mA/cm2 for the best solar cells from the PTB7, PTB7-Th and PBDT-TS1 blends, respectively, which agreed well with the Jsc values of the devices. The cell’s Voc is thermodynamically determined by the energy difference between the donor’s HOMO and the acceptor’s LUMO, ED-A. As the blended donor polymer was shifted from PTB7 to PTB7-Th, and PBDT-TS1, respectively, the Voc increased from 0.840 ± 0.006 to 0.876 ± 0.007 and 0.887 ± 0.005 V, respectively, which was well consistent with the down trend of the HOMO energy, going from −5.02 eV to −5.17 eV and −5.26 eV (Figure 1c). The Jsc increased from 8.46 ± 0.19 to 11.14 ± 0.21, and 13.23 ± 0.19 mA/cm2, respectively, with the polymer shifting from PTB7 to PTB7-Th and PBDT-TS1. Red-shifting of absorption edge of the polymer donor led to a wider spectral coverage of the solar emission (Figure 3c), contributing to the increase of Jsc. Again, the increase in both the hole and electron mobilities (Table 2) contributed to the increase of Jsc. Figure 3d and 3e as well as S6 are the 1D and 2D GIXRD data of the corresponding solar cell blends. All three polymers shown preferable face-on


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orientation in either neat or blended films with stronger (010) diffraction intensity along the outof-plane than along the in-plane direction. The (010) diffraction appeared at 2θ = 22.8° for PTB7, 22.6° for PTB7-Th and 24.2° for PBDT-TS1 in their neat films. As blended with PDI acceptor, the (010) diffraction of polymer shifts to 23.2°, 24.0° and 24.6° for PTB7, PTB7-Th and PBDTTS1, respectively, corresponding to a ππ−stacking distance of 0.38, 0.37, 0.36 nm, respectively. As we have observed, there were no obvious (010) diffractions seen from the PDI dimer, due to its highly twisted conformation.12 ππ−stacking of the polymer backbone becomes compacted, which was helpful for the holes transportation and contributed to the increase of the hole mobility. The out-of-plane (100) diffraction of the polymer in their neat films appeared at 4.8° for PTB7, 4.4° for PTB7-Th and 3.4° for PBDT-TS1, respectively. For the three blended films, the (100) diffractions all appeared at a close 2θ value of 4.0° along the out-of-plane. It was assumed to be mainly originated from the PDI dimer acceptor. TEM images (Figure S7) indicated three solar cell blends all shown nanoscale phase-separated black and white domains with the phase size all comparable to the exciton diffusion length. The estimated α value from PTB7 (0.938) is more deviated from one than that from other two polymers based solar cells (0.958 and 0.957) (Figure S8a). So does the n value (1.22 vs. 1.05 and 1.07 kT/q) (Figure S8b). Both the α and n values suggest that stronger nongeminate recombination losses for the mobile charges were involved for PTB7, which well explained the lower FF value for PTB7 based solar cell (Table 2). Again, the hole and electron mobilities from the PTB7 based solar cell became more unbalanced (µh/µe = 2.06) than other two cells (µh/µe = 1.17 and 0.87) (Table 2 and Figure S9).


12

(b)

(a) PEDOT/active layer/Al PEDOT/active layer/Ca/Al

-5

Jsc (mA/cm )

PEDOT/active layer/PDINO/Al

0.9

2

-2

1.0

α = 0.937 α = 0.953 α = 0.957

10

0

J / mAcm

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


-10 -15

1 0.8 n=1.32 n=1.08 n=1.07

0.1

-20 -10

-8

-6

-4 V/V

-2

0

1

10 2 Light Intensity (mW/cm )

Voc (V)

Page 13 of 23

0.7 100

Figure 4. Experimental J-V characteristics (a) and plots of Jsc and Voc versus the incident light power, P0, (b) of solar cells with different cathode layer, respectively. The photovoltaic results of PTB7-Th:PDI system suggested that the electron-transporting layer (ETL) had an impact on the solar cell performance, due to the different electron mobilities: 9.01×10-5 for the Ca layer and 1.03×10-4 for the PDINO layer. Here, we selected PBDT-TS1:PDI combination to study the effects of ETL and Table 2 collects the related photovoltaic results. Figure 4a and S10 display the J−V and EQE curves of the solar cells with Al, Ca/Al and PDINO/Al as the cathode, respectively. The current integrated from the EQE curves were 11.38, 11.85, and 12.59 mA/cm2 for the best solar cells with Al, Ca/Al and PDINO/Al as the cathode, respectively, in line with the Jsc values of the devices within 10% difference. Incorporation of the Ca layer helped dramatically reduce the bimolecular loss at the organic-to-metal interface, leading to an increase of FF and again Jsc. The n value was of 1.32 kT/q and 1.08 kT/q for the Al and Ca/Al cells, respectively (Figure 4b) and the α value was of 0.937 and 0.953, respectively. Both of the n and α values indicated that weaker bimolecular recombination loss was involved in the Ca/Al cell. Reduction of the bimolecular loss contributes to a higher charge collection probability, and hence, a higher Jsc (Figure 4a). Both the Ca/Al and PDINO/Al cells shown a close n value (1.08kT/q vs. 1.07kT/q) and also a close α value (0.953 vs. 0.957) (Figure 4b).


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However, the PDINO/Al cell showed a higher electron mobility than the Ca/Al cell (1.87 vs. 1.16×10-4 cm2V-1s-1) (Table 2 and Figure S11). As comparisons, the Ca/Al and Al cells both shown a close value of electron mobility. This suggests that the PDINO layer could afford an improved electron transportation than the Ca layer, which contributes to the higher electrical current generation, and, hence the higher Jsc and PCE. As shown in Table 2, processing the active layer with pure methanol only did not lead to an obvious change in Jsc and FF, while a slight decrease in Voc, indicating that the increase in Jsc with the cathode interlayer going from Ca to PDINO was contributed from the PDINO layer. We kindly note that a previous study on the PTB7:PC71BM system indicated the effects of methanol treatment on the bulk-heterojunction solar cell performance. 38 CONCLUSIONS In summary, a high-efficiency PDI based non-fullerene organic solar cell with a PCE of 6.94 ± 0.27% was achieved by optimizing both the hole and elctron mobilities via integration of filmmorphology optimization, polymer donor selection (from PTB7 to PTB7-Th and PBDT-TS1), and cathode interlayer engineering. With PTB7-Th as the donor, film-morphology optimizations using a combination of solvent annealing (SA) and solvent-vapour annealing (SVA) treatments led to a more balanced electron-to-hole mobility with respect to using the SA only, and a higher electron and hole mobilities both with respect to using the SVA only. As a result, the combination of SA and SVA yielded a trade-off between FF and Jsc, and, hence a higher PCE of 5.65 ± 0.20%. A replacement of PTB7-Th with the lower band gap PBDT-TS1 afforded an improved PCE of 6.94 ± 0.27% due to the improved absorption, and higher hole and electron mobilities. The cathode interlayer played an important role in solar cell’s performance: incorporation of Ca layer reduced bimolecular loss, giving a higher charge collection probability


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and a higher Jsc, while the PDINO layer afforded a higher electron mobility with respect to the Ca layer, leading to a higher electrical current generation. EXPERIMENTAL SECTION Solar cell Device fabrications and measurements. Indium tin oxide (ITO) coated glass substrates were pre-cleaned with deionized water, CMOS grade acetone and isopropanol in turn for 15 min. The organic residues were further removed by treating with UV-ozone for 1 h. Then they were coated with PEDOT: PSS (poly (3, 4-ethylenedioxythiophene): poly (styrene sulfonate)) (about 40 nm) at 2000 rpm for 35 s. After being baked at 150°C for ~ 15 min, the substrates were transferred into a nitrogen-filling glove box (< 0.1 ppm O2 & H2O). Atop that, active layers of polymer:PDI (D/A weight ratio was 1:1.5) were spin-coated from the o-DCB solution with 3% (v/v) DIO inside at 2000 rpm for 30 s. The donor-to-acceptor total concentration was of 30 mg/ml. The thickness of the photoactive layers was about 100 nm. After solvent or solvent-vapor annealing, methanol solution of PDINO (1 mg/mL) was deposited atop the active layer at 1000 rpm for 30 s. Finally, Al (ca. 80 nm), or Ca/Al (ca. 20 and 80 nm) were thermally evaporated at the vacuum of 2×10-6 Tor on top of the organic layer to make the sandwiched structure ITO/PEDOT: PSS/active layers/Ca (PDINO)/Al. The active area of the device was of 0.06 cm2. The current-voltage characteristics of all solar cell devices were measured with a Keithley 2400 source and conducted in a nitrogen-filling glove-box. An AM 1.5G solar simulator (AAA grade, XES-70S1) was used as the light source. The light intensity of the solar simulator is calibrated to be 100 mW/cm2 (at the position of sample) with a standard silicon reference solar cell (Area 20×20 mm2, the certification of the reference cell is accredited by NIST to the ISO-17025 standard). The EQE measurements were performed with the asfabricated solar cell in air using a QE-R3011 instrument (Enli Technology Co. Ltd., Taiwan).


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Supporting Information. Electron and hole mobility measurement, GIXRD images, EQE spectra, TEM images, and photovoltaic performance of the cell devices obtained under different conditions. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was financially supported by National Natural Science Foundation of China (No. 91433202, 91227112, 21327805 and 21221002), Chinese Academy of Sciences (XDB12010200), Minister of Science and Technology of P. R. China (2013CB933503 and 2012YQ120060). Beijing Synchrotron Radiation Facility (BSRF) is acknowledged for the GIXRD measurements. REFERENCES


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(1) Liu, Y.; Zhao, J.; Li, Z.; Mu, C.; Ma, W.; Hu, H.; Jiang, K.; Lin, H.; Ade, H.; Yan, H. Aggregation and Morphology Control Enables Multiple Cases of High-Efficiency Polymer Solar Cells. Nat. Commum. 2014, 5, 5293. (2) Zhao, J.; Li, Y.; Yang, G.; Jiang, K.; Lin, H.; Ade, H.; Ma, W.; Yan, H. Efficient Organic Solar Cells Processed from Hydrocarbon Solvents. Nat. Energy. 2016, 1, 15027. (3) Rajaram, S.; Shivanna, R.; Kandappa, S. K.; Narayan, K. S. Nonplanar Perylene Diimides as Potential Alternatives to Fullerenes in Organic Solar Cells. J. Phys. Chem. Lett. 2012, 3, 2405–2408. (4) Lu, Z.; Zhang, X.; Zhan, C.; Jiang, B.; Zhang, X.; Chen, L.; Yao, J. Impact of Molecular Solvophobicity vs. Solvophilicity on Device Performances of Dimeric Perylene Diimide Based Solution-Processed Non-Fullerene Organic Solar Cells. Phys. Chem. Chem. Phys. 2013, 15, 11375–11385. (5) Jiang, W.; Ye, L.; Li, X.; Xiao, C.; Tan, F.; Zhao, W.; Hou, J.; Wang, Z. Bay-Linked Perylene Bisimides as Promising Non-Fullerene Acceptors for Organic Solar Cells. Chem. Commun. 2014, 50, 1024–1026. (6) Zhong, Y.; Trinh, M. T.; Chen, R.; Wang, W.; Khlyabich, P. P.; Kumar, B.; Xu, Q.; Nam, C.Y.; Sfeir, M. Y.; Black, C.; Steigerwald, M. L.; Loo, Y.-L.; Xiao, S.; Ng, F.; Zhu, X.-Y.; Nuckolls, C. Efficient Organic Solar Cells with Helical Perylene Diimide Electron Acceptors. J. Am. Chem. Soc. 2014, 136, 15215–15221.


17


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 23

(7) Li, H.; Earmme, T.; Ren, G.; Saeki, A.; Yoshikawa, S.; Murari, N. M.; Subramaniyan, S.; Crane, M. J.; Seki, S.; Jenekhe, S. A. Beyond Fullerenes: Design of Nonfullerene Acceptors for Efficient Organic Photovoltaics. J. Am. Chem. Soc. 2014, 136, 14589–14597. (8) Mao, Z.; Senevirathna, W.; Liao, J. Y.; Gu, J.; Kesava, S. V.; Guo, C.; Gomez, E. D.; Sauvé, G. Azadipyrromethene-Based Zn(II) Complexes as Nonplanar Conjugated Electron Acceptors for Organic Photovoltaics. Adv. Mater. 2014, 26, 6290–6294. (9) Zhan, C.; Zhang, X.; Yao, J. New Advances in Non-Fullerene Acceptor Based Organic Solar Cells. RSC Adv. 2015, 5, 93002–93026. (10)

Zhou, Y.; Kurosawa, T.; Ma, W.; Guo, Y.; Fang, L.; Vandewal, K.; Diao, Y.; Wang, C.;

Yan, Q.; Reinspach, J.; Mei, J.; Appleton, A. L.; Koleilat, G. I.; Gao, Y.; Mannsfeld, S. C. B.; Salleo, A.; Ade, H.; Zhao, D.; Bao, Z. High Performance All-Polymer Solar Cell via Polymer Side-Chain Engineering. Adv. Mater. 2014, 26, 3767–3772. (11)

Jung, J. W.; Jo, J. W.; Chueh, C. C.; Liu, F.; Jo, W. H.; Russell, T. P.; Jen, A. K.-Y.

Fluoro-Substituted n-Type Conjugated Polymers for Additive-Free All-Polymer Bulk Heterojunction Solar Cells with High Power Conversion Efficiency of 6.71%. Adv. Mater. 2015, 27, 3310–3317. (12)

Wu, C.-H.; Chueh, C.-C.; Xi, Y.-Y.; Zhong, H.-L.; Gao, G.-P.; Wang, Z.-H.; Pozzo, L.

D.; Wen, T.-C.; Jen, A. K.-Y. Influence of Molecular Geometry of Perylene Diimide Dimers and Polymers on Bulk Heterojunction Morphology Toward High-Performance Nonfullerene Polymer Solar Cells. Adv. Funct. Mater. 2015, 25, 5326–5332.


18

Page 19 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(13)

Zhang, X.; Zhan, C.; Yao, J. Non-Fullerene Organic Solar Cells with 6.1% Efficiency

through Fine-Tuning Parameters of the Film-Forming Process. Chem. Mater. 2015, 27, 166– 173. (14)

Zhao, J.; Li, Y.; Lin, H.; Liu, Y.; Jiang, K.; Mu, C.; Ma, T.; Lai, J. Y. L.; Hu, H.; Yu, D.;

Yan, H. High-Efficiency Non-Fullerene Organic Solar Cells Enabled by a Difluorobenzothiadiazole-Based Donor Polymer Combined with a Properly Matched Small Molecule Acceptor. Energy Environ. Sci. 2015, 8, 520–525. (15)

Li, H.; Hwang, Y. J.; Courtright, B. A. E.; Eberle, F. N.; Subramaniyan, S.; Jenekhe, S.

A. Fine-Tuning the 3D Structure of Nonfullerene Electron Acceptors Toward HighPerformance Polymer Solar Cells. Adv. Mater. 2015, 27, 3266–3272. (16)

Lin, Y.; Wang, J.; Zhang, Z. G.; Bai, H.; Li, Y.; Zhu, D.; Zhan, X. An Electron Acceptor

Challenging Fullerenes for Efficient Polymer Solar Cells. Adv. Mater. 2015, 27, 1170–1174. (17)

Li, Y.; Liu, X.; Wu, F.-P.; Zhou, Y.; Jiang, Z.-Q.; Song, B.; Xia, Y.; Zhang, Z.-G.; Gao,

F.; Inganäs, O.; Li, Y.; Liao, L.-S. Non-Fullerene Acceptor with Low Energy Loss and High External Quantum Efficiency: Towards High Performance Polymer Solar Cells. J. Mater. Chem. A 2016, 4, 5890–5897. (18)

Zhong, H.; Wu, C.-H.; Li, C.-Z.; Carpenter, J.; Chueh, C.-C.; Chen, J.-Y.; Ade, H.; Jen,

A. K.-Y. Rigidifying Nonplanar Perylene Diimides by Ring Fusion Toward GeometryTunable Acceptors for High-Performance Fullerene-Free Solar Cells. Adv. Mater. 2016, 28, 951–958.


19


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(19)

Page 20 of 23

Kwon, O. K.; Uddin, M. A.; Park, J.-H.; Park, S. K.; Nguyen, T. L.; Woo, H. Y.; Park, S.

Y. A High Efficiency Nonfullerene Organic Solar Cell with Optimized Crystalline Organizations. Adv. Mater. 2016, 28, 910–916. (20)

Sun, D.; Meng, D.; Cai, Y.; Fan, B.; Li, Y.; Jiang, W.; Huo, L.; Sun, Y.; Wang, Z. Non-

Fullerene-Acceptor-Based Bulk-Heterojunction Organic Solar Cells with Efficiency over 7%. J. Am. Chem. Soc. 2015, 137, 11156–11162. (21)

Hwang, Y. J.; Courtright, B. A. E.; Ferreira, A. S.; Tolbert, S. H.; Jenekhe, S. A. 7.7%

Efficient All-Polymer Solar Cells. Adv. Mater. 2015, 27, 4578–4584. (22)

Zhang, X.; Yao, J.; Zhan, C. A Selenophenyl Bridged Perylene Diimide Dimer as an

Efficient Solution-Processable Small Molecule Acceptor. Chem. Commun. 2015, 51, 1058– 1061. (23)

Yan, Q. F.; Zhou, Y.; Zheng, Y. Q.; Pei, J.; Zhao, D. H. Towards Rational Design of

Organic Electron Acceptors for Photovoltaics: A Study Based on Perylenediimide Derivatives. Chem. Sci. 2013, 4, 4389–4394. (24)

Ye, L.; Jiang, W.; Zhao, W.; Zhang, S.; Cui, Y.; Wang, Z.; Hou, J. Toward Efficient

Non-Fullerene Polymer Solar Cells: Selection of Donor Polymers. Org. Electron. 2015, 17, 295–303. (25)

Aluicio-Sarduy, E.; Singh, R.; Kan, Z.; Ye, T.; Baidak, A.; Calloni, A.; Berti, G.; Duò,

L.; Iosifidis, A.; Beaupré, S.; Leclerc, M.; Butt, H.-J.; Floudas, G.; Keivanidis, P. E. Elucidating the Impact of Molecular Packing and Device Architecture on the Performance of


20

Page 21 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Nanostructured Perylene Diimide Solar Cells. ACS Appl. Mater. & Interfaces 2015, 7, 8687– 8698. (26)

Chen, Y.; Zhang, X.; Zhan, C.; Yao, J. In-Depth Understanding of Photocurrent

Enhancement in Solution-Processed Small-Molecule: Perylene Diimide Non-Fullerene Organic Solar Cells. Phys. Status Solidi A 2015, 212, 1961–1968. (27)

Wang, F.; Tan, Z.; Li, Y. Solution-Processable Metal Oxides/Chelates as Electrode

Buffer Layers for Efficient and Stable Polymer Solar Cells. Energy Environ. Sci. 2015, 8, 1059–1091. (28)

Braun, S.; Salaneck W. R.; Fahlman, M. Energy-Level Alignment at Organic/Metal and

Organic/Organic Interfaces. Adv. Mater. 2009, 21, 1450–1472. (29)

He, Z.; Wu, H.; Cao, Y. Recent Advances in Polymer Solar Cells: Realization of High

Device Performance by Incorporating Water/Alcohol-Soluble Conjugated Polymers as Electrode Buffer Layer. Adv. Mater. 2014, 26, 1006–1024. (30)

Steim, R.; Koglera, F. R.; Brabec, C. J. Interface Materials for Organic Solar Cells. J.

Mater. Chem. 2010, 20, 2499–2512. (31)

Lu, L.; Yu, L. Understanding Low Bandgap Polymer PTB7 and Optimizing Polymer

Solar Cells Based on It. Adv. Mater. 2014, 26, 4413–4430. (32)

Liao, S. H.; Jhuo, H. J.; Cheng, Y. S.; Chen, S. A. Fullerene Derivative-Doped Zinc

Oxide Nanofilm as the Cathode of Inverted Polymer Solar Cells with Low-Bandgap Polymer (PTB7-Th) for High Performance. Adv. Mater. 2013, 25, 4766–4771.


21


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Page 22 of 23

Zhang, S.; Ye, L.; Zhan, W.; Yang, B.; Wang, Q.; Hou, J. Realizing over 10% Efficiency

in Polymer Solar Cell by Device Optimization. Sci. China Chem. 2015, 58, 248–256. (34)

Zhang, Z.; Qi, B.; Jin, Z.; Chi, D.; Qi, Z.; Li, Y.; Wang, J. Perylene Diimides: A

Thickness-Insensitive Cathode Interlayer for High Performance Polymer Solar Cells. Energy Environ. Sci. 2014, 7, 1966–1973. (35)

Min, J.; Zhang, Z.-G.; Hou, Y.; Quiroz, C. O. R.; Przybilla, T.; Bronnbauer, C.; Guo, F.;

Forberich, K.; Azimi, H.; Ameri, T.; Spiecker, E.; Li, Y.; Brabec, C. J. Interface Engineering of Perovskite Hybrid Solar Cells with Solution-Processed Perylene−Diimide Heterojunctions toward High Performance. Chem. Mater. 2015, 27, 227–234. (36)

Müller-Buschbaum, P. The Active Layer Morphology of Organic Solar Cells Probed with

Grazing Incidence Scattering Techniques. Adv. Mater. 2014, 26, 7692–7709. (37)

Cowan, S. R.; Roy, A.; Heeger, A. J. Recombination in Polymer-Fullerene Bulk

Heterojunction Solar Cells. Phys. Rev. B 2010, 82, 245207. (38)

Guo, S.; Cao, B.; Wang, W.; Moulin, J.-F.; Müller-Buschbaum, P. Effect of Alcohol

Treatment on the Performance of PTB7:PC71BM Bulk Heterojunction Solar Cells. ACS Appl. Mater. Interfaces 2015, 7, 4641–4649.


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ToC

0

J / mAcm-2

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-5

Engineering Morphology + D/A combination + Cathode

-10

-15 0.0

0.2

0.4

0.6

0.8

V/V


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High-Efficiency Nonfullerene Polymer Solar Cell Enabling by

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