Revealing the Effect of Additives with Different Solubility on the

Subscriber access provided by - Access paid by the | UCSB Libraries

Article

Revealing the Effect of Additives with Different Solubility on the Morphology and the Donor Crystalline Structures of Organic Solar Cells Jiao Zhao, Suling Zhao, Zheng Xu, Bo Qiao, Di Huang, Ling Zhao, Yang Li, Youqin Zhu, and Peng Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b02671 • Publication Date (Web): 22 Jun 2016 Downloaded from http://pubs.acs.org on June 23, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 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

ACS Applied Materials & Interfaces

Revealing the Effect of Additives with Different Solubility on the Morphology and the Donor Crystalline Structures of Organic Solar Cells Jiao Zhao,†,‡ Suling Zhao,*, † , ‡ Zheng Xu, †,‡ Bo Qiao, †,‡ Di Huang, †,‡ Ling Zhao,†,‡ Yang Li,†,‡ Youqin Zhu†,‡and Peng Wang†,‡ †Key

Laboratory of Luminescence and Optical Information (Beijing Jiaotong University),

Ministry of Education, Beijing, 100044, China ‡Institute

of Optoelectronics Technology, Beijing Jiaotong University, Beijing, 100044, China

ABSTRACT: The impact of two kinds of additives, such as 1,8-octanedithiol (ODT) and 1,8-diiodooctane (DIO), diphenylether (DPE) and 1-chloronaphthalene (CN),

on

the

performance

of

poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3’’’-di(2-octyldodecyl)2,2’;5 ’,2’’;5’’,2’’’-quaterthiophen-5,5’’’-diyl)] (PffBT4T-2OD) : [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) based polymer solar cell are investigated. The polymer solar cells (PSCs) of PffBT4T-2OD:PC71BM by using CN show a more improved PCE of 10.23%. The solubility difference of PffBT4T-2OD in DIO and CN creates the fine transformation in phase separation and favorable nanoscale morphology. Grazing Incidence X-Ray Diffraction (GIXRD) data clearly shows molecular stacking and orientation of the active layer. Interestingly, DIO and CN have different functions on the effect of the molecular orientation. These interesting studies provide important guidance to optimize and control complicated molecular orientations and nanoscale morphology of PffBT4T-2OD based thick films for the application in PSCs.

KEYWORDS: polymer solar cell, solution additive, morphology, high efficiency, molecular orientation effect

INTRODUCTION

ACS Paragon Plus Environment


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 2 of 17

Organic polymer solar cells are considered as the important source of power in the future development of society because they have irreplaceable advantages, such as low cost of material, environment friendly, solution method, flexible thin film device and producing large area size1-3. Over the past few decades, the progress of polymer solar cells have made great achievements. The photoelectric conversion efficiency of polymer solar cells has exceeded 10% of the demand for industrial production4-6. Recently,

it

was

reported

that

a

new

type

of

material

poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3’’’-di(2-octyldodecyl) 2,2’;5’,2’’;5’’,2’’’-quaterthiophen-5,5’’’-diyl)] (PffBT4T-2OD) has a wide absorption range, high crystallinity and high hole mobility7, which made excellent improved properties of polymer solar cells8. The PSCs based on PffBT4T-2OD:PC71BM exhibit high fill factors (FFs) and photoelectric conversion efficiency even if the thickness of the active layer was about 300 nm9-11. To these thick films, the phase-separated and molecular order of BHJ blends are very important to the efficient charge separation and continuous transmission because the excition diffusion length in the photoactive layer of PSCs is quite limited in the scale of 10～20nm12. Morphological studies performed on BHJ systems have revealed that the nanoscale ordering in the thick film can be regulated through a wide variety of treatments such as prepared from different conditions for films, thermal and solvent annealing, add different types of solvent additives13-15. And it is the addition of solvent processing additive that is not only convenient but also effective, even though the understanding of the mechanism of the additive function remains unclear16-18. To date, various processing efforts to advance the active layer’s morphology in PffBT4T-2OD based PSCs have been studied by changing the polymer crystallinity, temperature, different fullerenes, non-PCBM domain size, different suitable solvent and molecular weight( M w )7, 19-20, with doping additive being one of the most convenient method. However, the aggregation and nanoscale ordering properties of PffBT4T-2OD:PC71BM based PSCs by doping additives are still unclear. The frequently used additives, like 1,8-octanedithiol (ODT), 1,8-diiodooctane (DIO), they are the same type of solution additives21. It is generally considered that


Page 3 of 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


these high boiling point additives dissolve PC71BM aggregates selectively. Therefore, PC71BM is allowed to penetrate into polymer domains and promote to form optimal thick-film morphology of the active layer. By contrast, some additives, such as 1-chloronaphthalene (CN) and diphenylether (DPE), are not only have the effect of the dispersed PC71BM, but also can dissolve some polymers22-23. It was reported that CN as the additive plays a role of cosolvent for the donor and acceptor materials, which could help to improve the crystalline structure and form a good charge transport channel and reduce the bimolecular recombination24-26. These results support the fabrication of efficient thick film PSCs for high-performance single layer devices. However, the mechanism of different kinds of additives with diverse solubility to donor or acceptor materials effect on the aggregation of polymer molecular is not investigated deeply for PffBT4T-2OD based solar cells. In which direction crystallization is enhanced by the soluble or dissoluble additives, and how these crystallization is favorable to the charge transport or the light absorption, are needed to be investigated further to heighten the performance of PffBT4T-2OD based solar cells27. In this paper, the effects of different solubility to the donor PffBT4T-2OD were studied on the nanoscale ordering of the polymer fiber networks. ODT and DIO were chosen as a kind of additives which can dissolve the acceptor PC71BM molecular only, while DPE and CN were used as another kind of additives which can dissolve both of the acceptor and the donor molecular. The polymer solar cells (PSCs) of PffBT4T-2OD:PC71BM by using CN as the additive showed more improved PCE of 10.23%. The PffBT4T-2OD and PC71BM blend films by adding DIO and CN showed diametrically opposed structural order and morphology acquired by the Atomic Force Microscopy (AFM) and Grazing Incidence X-Ray Diffraction (GIXRD).

EXPERIMENTAL SECTION It was according to the device architecture that PSCs were fabricated demonstrated in Figure 1a. The indium tin oxide (ITO) were cleaned in a ultrasonic cleaner which was sputtered onto glass substrates with a resistance 15Ω/cm2，through mixing a little



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

abluent, deioned water and ethanol, which was washed once every 30 minutes and repeated three times, followed drying with nitrogen-gas, put in the petri dish for 30 minutes. In order to improve the cleanliness and surface work function of ITO substrate, the pretreated process with ultraviolet ozone for 7min was essential. The aqueous solution of polyethylenedioxy-thiophene:polystyrenesulfonate (PEDOT:PSS, Clevios Al4083), was filtered by 0.45µm filter and then spun on processed ITO surface at 4500rpm/50s and baked for 15min in the atmosphere at the temperature of 150°C. The polymer PffBT4T-2OD and PC71BM were purchased from 1-Material. Different solvent additives with 3%(v/v) were added separately to the mixed solution of 1,2-dichlorobenzene (DCB) and chlorobenzene (CB) with each half of the total volume. The weight ratio of PffBT4T-2OD:PC71BM was 1:1.3 and the conclusive concentration of blend solution was 32.2mg/ml. Then PffBT4T-2OD:PC71BM solutions were stirred overnight at 110°C in a glove box and spined (1000rpm, 25s) onto warm substrates which were heated to 110°C on the heating platform then annealed at 80°C for 10min. The cathode modified layer of lithium fluoride (LiF) (1 nm) and the electrode layer of aluminium (100 nm) were deposited on the active layer respectively under 2.5×10-4Pa via a thermally evaporation. The effective area of polymer solar cell device was tested to be 4mm2. The current density-voltage (J-V) of the devices were measured under simulated AM 1.5G illumination (100mW/cm2) using an ABET Sun 2000. The J−V characteristics were investigated through a Keithley 4200 source meter under atmosphere. Before the J-V test, a calibrated Si photodiode which was adopted to check the total illumination intensity. The external quantum efficiencies (EQEs) data were recorded using a Zolix Solar Cell Scan 100 with a chopper-modulated of 178Hz. With a calibrated silicon reference cell, these measurements were converted to EQE. The UV-vis absorption spectra of active layers were acquired by a Shimadzu UV-3101 PC spectrophotometer. The morphology and phase images of active layers were performed by using atomic force microscopy (AFM) in tapping mode with the scan size of 2 × 2um2 by a multimode Nanoscope IIIa operated. Grazing Incidence X-Ray Diffraction (GIXRD) was measured at 1W1A, Beijing Synchrotron Radiation Facility (BSRF). The Samples that were spin-coated


Page 4 of 17

Page 5 of 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


on quartz substrates used the same blend solutions as those adopted in devices for UV-VIs, GIXRD, AFM and all the measurements were performed in the air.

Figure 1. (a) Bulk heterojunction solar cell structure. (b) Energy level diagram of the ingredients of the device. (c) Molecular structures of the solvents additives investigated in this work.

RESULTS AND DISCUSSION BHJ

solar

cells

were

created

as

the

conformation

of

ITO/PEDOT:PSS/PffBT4T-2OD:PC71BM/LiF/Al. Figure 2a depicts the current density–voltage (J-V) curves for solar cells adopted different treatments. The corresponding photovoltaic parameters are summarized in Table 1. The devices with CN and DPE additives show higher performance than those with additive DIO and ODT and those without additives. It means that additives dissolving both donor and acceptor molecular are more favorable than those dissolving only acceptor molecular to the performance of PffBT4T-2OD:PC71BM based solar cells. The PCE of the device with CN dramatically increased up to 10.249% contrasted with that without additive devices and the short-circuit current density increases from 15.896 to 17.752mA/cm2 and the fill factor (FF) increases from 64.4% to 73.1%. The enhancive FF of the cells obtained with CN and DPE additives can be partly attributed to the reduced series resistance (Rs) derived from the slope of the cell J−V curve under forward bias (under illumination) and to the increased shunt resistance (Rsh) stemed



from the slope in the third quadrant of J−V curve. The smaller Rs indicates that there is a favorable charge transport way formed in the photovoltaic layer processed with additives. On the other side, the larger Rsh indicates a small reverse current density of the devices. Even Rs of the devices with DIO and ODT become smaller than that of the devices without any additive, but Rsh changes little or becomes smaller for the device with ODT. The performance of their corresponding solar cells is not enhanced greatly even weaken slightly. Therefore, it is concluded that suitable additives to process the active layer can help with the charge transporting, then FF of corresponding devices is improved. The EQE data of the cells without additives and with DIO and CN as examples, shown in Figure 2b, give the above confirmation again. The EQE of PSCs prepared with CN additive has a maximum value of 82.9%, because of the highly efficient photoelectron conversion process, including light absorption, exciton dissociation and charge transportation. The PSCs with DIO treated demonstrates secondary EQE values, meanwhile the PSCs without any additives presents the minimum EQE value. The enhanced EQE spectrum indicates an enhanced Jsc value. The Jsc values, which were measured by the integration of EQE response, are in accord well with those obtained from the J−V characteristics under illumination. For these excellent photovoltaic properties and the ordered molecular stacking, they are in a close relationship.

b)

a) 0

80

pure 3% ODT 3% DIO 3% DPE 3% CN

-2 -4 -6 -8 -10

70 60

EQE(%)

current density(mA/cm2)

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 6 of 17

-12 -14 -16

50

Pure 3% DIO 3% CN

40 30 20 10

-18 0.0

0.2

0.4

0.6

0.8

0 300

400

Voltage(V)

500

600

700

800

Wavalength(nm)

Figure 2. a) Current density-voltage (J-V) characteristics of the PSCs based on PffBT4T-2OD:PC71BM with or without additives, under illumination of AM 1.5G 100mW/cm2. b) EQE spectra with different additives.


Page 7 of 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


Table 1. The photovoltaic performance of OPVs based on the PffBT4T-2OD:PC71BM blend films in different solvent additives. The values a in square brackets are the average PCE obtained from 10 devices.

The

absorption

spectra

of

pure

and

with

DIO

and

CN

additives

PffBT4T-2OD:PC71BM active films spin-coated on quartz at 1000 rpm were detected respectively, as shown in Figure 3a. All films possess the same absorption form, which indicates that there are no new materials formed in the processed films by adding additives. We found the strongest absorption in the range of 350~625nm in the blend film processed through CN, but in the range of 625~695nm the blend film with DIO also has strongest absorption. The absorption change could be main contribution to the more ordered morphology structure of PffBT4T-2OD with the process of additives28, and the increase of Jsc and EQE of PSCs have benefited from crystalline morphology. But the enhanced absorption of films with additives is not distinct compared with the EQE of corresponding devices. We concluded that the changes of absorption intensities of films with solvent additive is not the main factor to the enhanced Jsc. Furthermore to probe deeply into the effect of DIO and CN on property of PSCs, the relationship between effective voltage (Veff) and photocurrent (Jph) of cells has been studied and observerd in Figure 3b. It is well known that during the Veff = Vo-Va, where Vo is the voltage at which Jph = 0 and then Va is the applied bias voltage29. Also about Jph =JL - JD, where JL is referred to as the current density under illumination and JD is the corresponding density in the dark30. The saturation photocurrent density (Jsat) was used to go further with the information in detail through the PSC devices based



on the photocurrent analysis. As for the Jph /Jsat ratios, they can be adopted to evaluate the charge carrier collection and efficiency of exciton dissociation，which should be under maximum power output conditions or short circuit conditions30-31. The Jph/Jsat under short circuit conditions without additive or with DIO or CN at ratio is 94.67%, 95.96% and 97.16% respectively. The slightly enlarger Jph /Jsat ratios value of the device with 3% CN, which indicates that the suitable solvent additives will promote exciton dissociation and charge transport.

b) pure 3% DIO 3% CN

1.2 1.0 0.8 0.6 0.4

pure 3% DIO 3% CN

1

0.2 0.0 300

10

Jph(mA/cm2)

a)

Norm.Abs.

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 8 of 17

400

500

600

700

800

0.1

Wavalength(nm)

Veff(V)

1

Figure 3. a) Normalized absorption spectra of PffBT4T-2OD:PC71BM films by the thickness. b) Jph-Veff curves of the solar cell with/without different additives. The charge transporting has a connection with the microstructure and the penetrating network of the active layer. Different solution addictives can lead to imparities in Jsc and FF, and the benefit of nano morphology usually gives rise to the enhanced device performance. To further understand the charge transport performance with different types of additives, DIO and CN, in this study, AFM and GIXRD were used to reveal the correlation between the device performance and the polymer:fullerene nanoscale morphology32. The PSCs performance are in a close relationship with the morphology of the active layer of the PffBT4T-2OD:PC71BM thick film. The nanoscale sufficient phase separation can increase photo-generated excitons dissociation probability. Fibrous continuous networks benefit the effective charge transport. Those lead to the simultaneous increase of Jsc and FF of the devices33. Figure 4 demonstrates the surface morphology variations of the active layer after adding additives. As is shown clearly, DIO can effectively dissolve fullerene derivatives. However, it is also a poor solvent for donor material, which will result in


Page 9 of 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


polymer aggregation into more crystalline phases and form nanoscale phase separation. Such organized ordering brings about larger polymer domains leading to higher roughness of the active layer surface. However, the polymer of PffBT4T-2OD can be dissolved in a certain amount of CN, which would change a little in the thick film morphology. Five different areas of each sample were tested and then the average roughness value were calculated by AFM. The surface roughness of the thick film in average without additive is 2.10nm. However, the average surface roughness of the films with DIO or CN get increased to 2.91 and 2.30nm, respectively. Compared to the film with DIO, the blend film is smoother with CN , and the junction between the photovoltaic layer and cathode can be boosted by the sleek surface, which can produce better transmission channel to the cathode in the bulk heterojunction system34. Notably, through adding the additives, the surface roughness of the thick films becomes larger, showing a higher crystalline structures of the corresponding PSCs35-36. Compared to DIO, the CN displayed much more improved mixing between D:A and formation of interpenetrating networks, and the networks have decreased grain boundaries and should supply continuous pathways for charge carrier migration to the anode or cathode, promoting high fill factors and Jsc values by suppressing charge accumulation and non-geminate recombination21, 37.

Figure 4. AFM height images (2×2um, vertical scale 30nm) of optimized PffBT4T-2OD:PC71BM blends from: (a) CB+DCB, (b) CB+DCB with 3% vol DIO, (c) CB+DCB with 3% vol CN. The root-mean-square (RMS) roughness is 2.10nm



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

2.91nm 2.30nm from (a), (b) and (c), (d)-(f) phase images (2×2um) The crystallization of PffBT4T-2OD in blends are characterized by using GIXRD, which was doomed as an auxiliary tool, in the aspect of organic electronics, to describe a film as ordered or not in a qualitative manner among the different processing films

38

. Figure 5 (a), (b) and (c) present GIWAXS patterns of the

PffBT4T-2OD:PC71BM blend films processed without and with the additives. The lamellar construction which was relative to the edge- and face- orientation packing of the PffBT4T-2OD could be detected by above-mentioned patterns. GIXRD data were presented in Figure 5 (d) and (e), which are employ the out-of-plane pattern and in-plane pattern to study the crystalline direction of the PffBT4T-2OD:PC71BM films treated with additives or not. The diffraction corresponding to PC71BM does not change in different films, which show that the difference in performance of the devices mainly comes from polymer molecules to rearrange affect by the different additives. CN dissolve the polymer and its high boiling point can be initiatively driven to alkyl chain to rearrange the polymer molecules in the process of the film formation. For PffBT4T-2OD, DIO is a much poorer solvent, compared with CN, and it will result in passive promote crystallization.39-40 In the GIXRD experiment data, the diffraction of (x00) (x=1,2,3) and (010) of PffBT4T-2OD in two configurations were detected and their intensity is different for the films processed with additives. According figure 5 (d), all the peaks are in the same position (q = 0.29Å−1 and q = 1.79Å−1) mean that the similar lamellar spacing in different directions from Bragg equation were revealed in all the blend films. It is interesting to note that the intensity of π−π stacking peak (010) of PffBT4T-2OD is more significant in the out-of-plane direction than that in the in-plane direction, which indicates a forcefully prioritized face-on direction relative to the substrate. The crystallization of PffBT4T-2OD along the face-on direction is good for the charge transport in the direction across the active layer8. The face-on π−π stacking peak (010) of the blend thick film becomes stronger by addition of DIO. It means that DIO is beneficial to the crystallinity of PffBT4T-2OD, which results in the well charge transport41. In contrast to the blend thick film with DIO, the CN additive thick film GIXRD data shows a better-defined


Page 10 of 17

Page 11 of 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


(100), (200), and even (300) diffraction peaks of PffBT4T-2OD located at qz = 0.29, 0.59, and 0.88Å–1 observed in the out-of-plane direction, which corresponds to the crystallization along the branched alkyl chains42-43. The structural parameters of PffBT4T-2OD:PC71BM films processed with and without additives were analyzed by using Debye-Scherrer equation:

Where K is the Scherrer constant. D is the average size of crystalline domains in the perpendicular direction to the crystal surface. B is the full width at half maximum of the diffraction peak. θ is the diffraction angle, and γ is x-ray wavelength44-45. According to the calculated results shown in table 2, the crystal dimensions of PffBT4T-2OD is affected by additives. CN, dissolves both PffBT4T-2OD and PC71BM, leads to enhanced crystallinity PffBT4T-2OD in (100) direction corresponding to the alkyl stacking peak located at a value of qz of 0.29Å–1. The corresponding average size D is 12.30nm for the CN additive film. DIO, which dissolves only PC71BM, has more profound effects on the crystallization of PffBT4T-2OD in π-π stacking direction (010), in which the largest crystal dimension is 4.948nm. However, the crystallization of PffBT4T-2OD in the film by adding CN, in spite of the direction of alkyl stacking, is more improved when compared with pure or adding DIO films. The enhanced crystalline content and elevated crystal are good for the charge transport in active layer by adding CN, which can result in the improved Jsc and FF. So it is significant to find that different choices of additives will lead to differences in the areas of controlling both the film’s morphology and crystalline structure.



e)

d)

10000

out-of-plane

（ 100）

pure 3% DIO 3% CN （ 200）（ 300） PC71BM

（ 010）

1000

10000

Intensity(a.u)

100000

intensity(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

Page 12 of 17

（ 100）

In-plane pure 3% DIO 3% CN （ 200）

PC71BM

1000 （ 010）

100 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

100 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

o

qz(A-1)

o

qxy(A-1)

Figure 5. Two-dimensional GIWAXS patterns of the active layer with different treatments, (a) no treatment, (b) processed with DIO, (c) processed with CN. (d) grazing incident angle with out-of-plane and (e) in-plane scattering geometry for PffBT4T-2OD:PC71BM films with different additive. Table 2. (100) and (010) crystal dimensions of PffBT4T-2OD:PC71BM films with different additives and without additive.

CONCLUSIONS In this contribution, two different addictive treatments in PffBT4T-2OD-based films were studied in depth to control morphology and enhance device performance. The performance of BHJ PSCs processed by the additive (CN) dissolving both of donor and acceptor molecular enhanced more than that of BHJ PSCs processed by the additive (DIO) dissolving only acceptor molecular. The prepared BHJ PSCs with CN treated had a high Jsc, FF and PCE up to 17.752 mA/cm2, 73.1% and 10.25%, respectively. The improvement of PCE came from the melioratived thick film nanoscale morphology and molecular orientation of active layer, which in return facilitate charge transport within the active layer. It is found that DIO and CN have an influence on the molecular orientation of BHJ thick films in different direction


Page 13 of 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


demonstrated by the grazing-incidence X-ray diffraction (GIXRD). The diffraction of (x00) of PffBT4T-2OD in the blend film processed by CN was more improved with a relatively large size, which corresponds to the alkyl stacking and in sequence contributes the charge transport within the photovoltaic films. By adding DIO, the blend film shown a preferable crystallization in π-π stacking direction (010) with a relative small size, which is favorable to the charge transport across the BHJ film. Therefore, BHJ PSCs processed by CN and DIO show higher performance than pure BHJ PSCs. But CN is one of the ideal additives for PffBT4T-2OD-based BHJ.

AUTHOR INFORMATION Corresponding Author *E-mail address: [email protected], Tel (Fax):86-10-51684462.

Notes The authors declare no competing financial interest

ACKNOWLEDGMENTS This work was supported by the Research Fund for the Doctoral Program of Higher Education (No.20120009130005 and 20130009130001), and the Fundamental Research Funds for the National Natural Science Foundation of China (No. 61575019, 51272022 and 11474018). Part of this work was fulfilled on the basis of data acquired at 1W1A, BSRF. The authors deeply appreciate the assistance of scientists of Diffuse X-ray Scattering Station in the experiments.

REFERENCES 1.

Tumbleston, J. R.; Collins, B. A.; Yang, L.; Stuart, A. C.; Gann, E.; Ma, W.; You, W.; Ade, H., The

Influence of Molecular Orientation on Organic Bulk Heterojunction Solar Cells. Nat. Photonics 2014, 8 (5), 385-391. 2.

van Franeker, J. J.; Heintges, G. H.; Schaefer, C.; Portale, G.; Li, W.; Wienk, M. M.; van der Schoot,

P.; Janssen, R. A., Polymer Solar Cells: Solubility Controls Fiber Network Formation. J. Am. Chem. Soc. 2015, 137 (36), 11783-11794. 3.

Lu, L.; Zheng, T.; Wu, Q.; Schneider, A. M.; Zhao, D.; Yu, L., Recent Advances in Bulk



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

Heterojunction Polymer Solar Cells. Chem. Rev. 2015, 115 (23), 12666–12731. 4.

Hu, H.; Jiang, K.; Yang, G.; Liu, J.; Li, Z.; Lin, H.; Liu, Y.; Zhao, J.; Zhang, J.; Huang, F.; Qu, Y.; Ma, W.;

Yan, H., Terthiophene-Based D-a Polymer with an Asymmetric Arrangement of Alkyl Chains That Enables Efficient Polymer Solar Cells. J. Am. Chem. Soc. 2015, 137 (44), 14149-14157. 5.

Lu, L.; Chen, W.; Xu, T.; Yu, L., High-Performance Ternary Blend Polymer Solar Cells Involving Both

Energy Transfer and Hole Relay Processes. Nat. Commun. 2015, 6, 7327. 6.

Huang, J.; Carpenter, J. H.; Li, C. Z.; Yu, J. S.; Ade, H.; Jen, A. K., Highly Efficient Organic Solar Cells

with Improved Vertical Donor-Acceptor Compositional Gradient Via an Inverted Off-Center Spinning Method. Adv. Mater. 2015, 28 (5), 967-974. 7.

Zhao, J.; Li, Y.; Lin, H.; Liu, Y.; Jiang, K.; Mu, C.; Ma, T.; Lin Lai, J. Y.; 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 (2), 520-525. 8.

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. Commun. 2014, 5, 5293. 9.

Choi, H.; Ko, S. J.; Kim, T.; Morin, P. O.; Walker, B.; Lee, B. H.; Leclerc, M.; Kim, J. Y.; Heeger, A. J.,

Small-Bandgap Polymer Solar Cells with Unprecedented Short-Circuit Current Density and High Fill Factor. Adv. Mater. 2015, 27 (21), 3318-3324. 10. Vohra, V.; Kawashima, K.; Kakara, T.; Koganezawa, T.; Osaka, I.; Takimiya, K.; Murata, H., Efficient Inverted Polymer Solar Cells Employing Favourable Molecular Orientation. Nat. Photonics 2015, 9 (6), 403-408. 11. Nguyen, T. L.; Choi, H.; Ko, S. J.; Uddin, M. A.; Walker, B.; Yum, S.; Jeong, J. E.; Yun, M. H.; Shin, T. J.; Hwang, S.; Kim, J. Y.; Woo, H. Y., Semi-Crystalline Photovoltaic Polymers with Efficiency Exceeding 9% in a ∼300 Nm Thick Conventional Single-Cell Device. Energy Environ. Sci. 2014, 7 (9), 3040-3051. 12. Wang, E.; Mammo, W.; Andersson, M. R., 25th Anniversary Article: Isoindigo-Based Polymers and Small Molecules for Bulk Heterojunction Solar Cells and Field Effect Transistors. Adv. Mater. 2014, 26 (12), 1801-1826. 13. Kniepert, J.; Lange, I.; Heidbrink, J.; Kurpiers, J.; Brenner, T. J. K.; Koster, L. J. A.; Neher, D., Effect of Solvent Additive on Generation, Recombination, and Extraction in Ptb7:Pcbm Solar Cells: A Conclusive Experimental and Numerical Simulation Study. J. Phys. Chem. C 2015, 119 (15), 8310-8320. 14. Kang, T. E.; Kim, T.; Wang, C.; Yoo, S.; Kim, B. J., Poly(Benzodithiophene) Homopolymer for High-Performance Polymer Solar Cells with Open-Circuit Voltage of near 1 V: A Superior Candidate to Substitute for Poly(3-Hexylthiophene) as Wide Bandgap Polymer. Chem. Mater. 2015, 27 (7), 2653-2658. 15. Earmme, T.; Hwang, Y. J.; Subramaniyan, S.; Jenekhe, S. A., All-Polymer Bulk Heterojuction Solar Cells with 4.8% Efficiency Achieved by Solution Processing from a Co-Solvent. Adv. Mater. 2014, 26 (35), 6080-6085. 16. Schmidt, K.; Tassone, C. J.; Niskala, J. R.; Yiu, A. T.; Lee, O. P.; Weiss, T. M.; Wang, C.; Frechet, J. M.; Beaujuge, P. M.; Toney, M. F., A Mechanistic Understanding of Processing Additive-Induced Efficiency Enhancement in Bulk Heterojunction Organic Solar Cells. Adv. Mater. 2014, 26 (2), 300-305. 17. Kwon, S.; Park, J. K.; Kim, G.; Kong, J.; Bazan, G. C.; Lee, K., Synergistic Effect of Processing Additives and Optical Spacers in Bulk-Heterojunction Solar Cells. Adv. Energy Mater. 2012, 2 (12), 1420-1424.


Page 14 of 17

Page 15 of 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


18. van Franeker, J. J.; Turbiez, M.; Li, W.; Wienk, M. M.; Janssen, R. A., A Real-Time Study of the Benefits of Co-Solvents in Polymer Solar Cell Processing. Nat. Commun. 2015, 6, 6229. 19. Ma, W.; Yang, G.; Jiang, K.; Carpenter, J. H.; Wu, Y.; Meng, X.; McAfee, T.; Zhao, J.; Zhu, C.; Wang, C.; Ade, H.; Yan, H., Influence of Processing Parameters and Molecular Weight on the Morphology and Properties of High-Performance Pffbt4t-2od:Pc71bm Organic Solar Cells. Adv. Energy Mater. 2015, 5 (23), 1501400. 20. Sprau, C.; Buss, F.; Wagner, M.; Landerer, D.; Koppitz, M.; Schulz, A.; Bahro, D.; Schabel, W.; Scharfer, P.; Colsmann, A., Highly Efficient Polymer Solar Cells Cast from Non-Halogenated Xylene/Anisaldehyde Solution. Energy Environ. Sci. 2015, 8 (9), 2744-2752. 21. Liu, C.; Hu, X.; Zhong, C.; Huang, M.; Wang, K.; Zhang, Z.; Gong, X.; Cao, Y.; Heeger, A. J., The Influence of Binary Processing Additives on the Performance of Polymer Solar Cells. Nanoscale 2014, 6 (23), 14297-14304. 22. Kwon, S.; Park, J. K.; Kim, J.; Kim, G.; Yu, K.; Lee, J.; Jo, Y.-R.; Kim, B.-J.; Kang, H.; Kim, J.; Kim, H.; Lee, K., In Situ Studies of the Molecular Packing Dynamics of Bulk-Heterojunction Solar Cells Induced by the Processing Additive 1-Chloronaphthalene. J. Mater. Chem. A 2015, 3 (15), 7719-7726. 23. Kim, Y.; Yeom, H. R.; Kim, J. Y.; Yang, C., High-Efficiency Polymer Solar Cells with a Cost-Effective Quinoxaline Polymer through Nanoscale Morphology Control Induced by Practical Processing Additives. Energy Environ. Sci. 2013, 6 (6), 1909-1916. 24. Li, M.; Liu, F.; Wan, X.; Ni, W.; Kan, B.; Feng, H.; Zhang, Q.; Yang, X.; Wang, Y.; Zhang, Y.; Shen, Y.; Russell, T. P.; Chen, Y., Subtle Balance between Length Scale of Phase Separation and Domain Purification in Small-Molecule Bulk-Heterojunction Blends under Solvent Vapor Treatment. Adv. Mater. 2015, 27 (40), 6296-6302. 25. Gao, F.; Himmelberger, S.; Andersson, M.; Hanifi, D.; Xia, Y.; Zhang, S.; Wang, J.; Hou, J.; Salleo, A.; Inganas, O., The Effect of Processing Additives on Energetic Disorder in Highly Efficient Organic Photovoltaics: A Case Study on Pbdttt-C-T:Pc71 Bm. Adv. Mater. 2015, 27 (26), 3868-3873. 26. Zhao, L.; Zhao, S.; Xu, Z.; Yang, Q.; Huang, D.; Xu, X., A Simple Method to Adjust the Morphology of Gradient Three-Dimensional Ptb7-Th:Pc71bm Polymer Solar Cells. Nanoscale 2015, 7 (12), 5537-5544. 27. Yang, B.; Zhang, P.; Wang, X.; Stancil, P. C.; Bowman, J. M.; Balakrishnan, N.; Forrey, R. C., Quantum Dynamics of Co-H(2) in Full Dimensionality. Nat. Commun. 2015, 6, 6629. 28. Gao, J.; Dou, L.; Chen, W.; Chen, C.-C.; Guo, X.; You, J.; Bob, B.; Chang, W.-H.; Strzalka, J.; Wang, C.; Li, G.; Yang, Y., Improving Structural Order for a High-Performance Diketopyrrolopyrrole-Based Polymer Solar Cell with a Thick Active Layer. Adv. Energy Mater. 2014, 4 (5), 1300739. 29. Wang, J.; Zhang, F.; An, Q.; Sun, Q.; Zhang, J.; Hu, B., Unique Insight into Phase Separation in Polymer Solar Cells from Their Electric Characteristics. Phys. Chem. Chem. Phys 2015, 17 (44), 29671-29678. 30. Lu, L.; Xu, T.; Chen, W.; Landry, E. S.; Yu, L., Ternary Blend Polymer Solar Cells with Enhanced Power Conversion Efficiency. Nat. Photonics 2014, 8 (9), 716-722. 31. He, Z.; Zhong, C.; Huang, X.; Wong, W. Y.; Wu, H.; Chen, L.; Su, S.; Cao, Y., Simultaneous Enhancement of Open‐Circuit Voltage, Short‐Circuit Current Density, and Fill Factor in Polymer Solar Cells. Adv. Mater. 2011, 23 (40), 4636-4643. 32. Heeger, A. J., 25th Anniversary Article: Bulk Heterojunction Solar Cells: Understanding the Mechanism of Operation. Adv. Mater. 2014, 26 (1), 10-27. 33. Muller-Buschbaum, P., The Active Layer Morphology of Organic Solar Cells Probed with Grazing



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

Incidence Scattering Techniques. Adv. Mater. 2014, 26 (46), 7692-7709. 34. Liu, J.; Sun, Y.; Moonsin, P.; Kuik, M.; Proctor, C. M.; Lin, J.; Hsu, B. B.; Promarak, V.; Heeger, A. J.; Nguyen, T. Q., Tri-Diketopyrrolopyrrole Molecular Donor Materials for High-Performance Solution-Processed Bulk Heterojunction Solar Cells. Adv. Mater. 2013, 25 (41), 5898-5903. 35. Peet, J.; Kim, J. Y.; Coates, N. E.; Ma, W. L.; Moses, D.; Heeger, A. J.; Bazan, G. C., Efficiency Enhancement in Low-Bandgap Polymer Solar Cells by Processing with Alkane Dithiols. Nat. Mater. 2007, 6 (7), 497-500. 36. Park, J. K.; Kim, C.; Walker, B.; Nguyen, T.-Q.; Seo, J. H., Morphology Control of Solution Processable Small Molecule Bulk Heterojunction Solar Cells Via Solvent Additives. RSC. Adv. 2012, 2 (6), 2232-2234. 37. Wang, D. H.; Kyaw, A. K. K.; Pouliot, J.-R.; Leclerc, M.; Heeger, A. J., Enhanced Power Conversion Efficiency of Low Band-Gap Polymer Solar Cells by Insertion of Optimized Binary Processing Additives. Adv. Energy Mater. 2014, 4 (4), 1300835. 38. Rivnay, J.; Mannsfeld, S. C.; Miller, C. E.; Salleo, A.; Toney, M. F., Quantitative Determination of Organic Semiconductor Microstructure from the Molecular to Device Scale. Chem. Rev. 2012, 112 (10), 5488-5519. 39. 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 (2), 15027. 40. Zhou, W.; Xie, Y.; Hu, X.; Zhang, L.; Meng, X.; Zhang, Y.; Ma, W.; Chen, Y., Surface Treatment by Binary Solvents Induces the Crystallization of a Small Molecular Donor for Enhanced Photovoltaic Performance. Phys. Chem. Chem. Phys 2015, 18 (2), 735-742. 41. Liu, C.-M.; Su, Y.-W.; Jiang, J.-M.; Chen, H.-C.; Lin, S.-W.; Su, C.-J.; Jeng, U. S.; Wei, K.-H., Complementary Solvent Additives Tune the Orientation of Polymer Lamellae, Reduce the Sizes of Aggregated Fullerene Domains, and Enhance the Performance of Bulk Heterojunction Solar Cells. J. Mater. Chem. A 2014, 2 (48), 20760-20769. 42. Gevaerts, V. S.; Herzig, E. M.; Kirkus, M.; Hendriks, K. H.; Wienk, M. M.; Perlich, J.; Müller-Buschbaum, P.; Janssen, R. A. J., Influence of the Position of the Side Chain on Crystallization and Solar Cell Performance of Dpp-Based Small Molecules. Chem. Mater. 2014, 26 (2), 916-926. 43. de Jeu, W. H.; Rahimi, K.; Ziener, U.; Vill, R.; Herzig, E. M.; Muller-Buschbaum, P.; Moller, M.; Mourran, A., Substituted Septithiophenes with End Groups of Different Size: Packing and Frustration in Bulk and Thin Films. Langmuir 2016, 32 (6), 1533-1541. 44. Rivnay, J.; Mannsfeld, S. C. B.; Miller, C. E.; Salleo, A.; Toney, M. F., Quantitative Determination of Organic Semiconductor Microstructure from the Molecular to Device Scale. Chem. Rev. 2012, 112 (10), 5488-5519. 45. Mahyar, A.; Ali Behnajady, M.; Modirshahla, N., Characterization and Photocatalytic Activity of Sio2-Tio2 Mixed Oxide Nanoparticles Prepared by Sol-Gel Method. Indian. J.chem. Sec. A 2010, 49 (12), 1593-1600.


Page 16 of 17

Page 17 of 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


Table of Contents


Revealing the Effect of Additives with Different Solubility on the

Recommend Documents