Thermal Annealing Effect on Ultrafast Charge Transfer in All-Polymer

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Thermal Annealing Effect on Ultrafast Charge Transfer in AllPolymer Solar Cells with a Non-Fullerene Acceptor N2200 Feng Jin, Guanqun Ding, Yuning Wang, Jianyu Yuan, Wenping Guo, Haochen Yuan, Chuanxiang Sheng, Wanli Ma, and Haibin Zhao J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b03001 • Publication Date (Web): 05 Apr 2017 Downloaded from http://pubs.acs.org on April 8, 2017

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The Journal of Physical Chemistry

Thermal Annealing Effect on Ultrafast Charge Transfer in All-Polymer Solar Cells with a Non-Fullerene Acceptor N2200 Feng Jin,† Guanqun Ding,‡ Yuning Wang,§ Jianyu Yuan,‡ Wenping Guo,† Haochen Yuan,† Chuanxiang Sheng,*,§ Wanli Ma,*,‡ and Haibin Zhao*,† †

Shanghai Ultra-precision Optical Manufacturing Engineering Research Center, and Key

Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Department of Optical Science and Engineering, Fudan University, Shanghai, 200433, China. ‡

Institute of Functional Nano & Soft Materials (FUNSOM) & Collaborative Innovation Center of

Suzhou Nano Science and Technology, Soochow University, Suzhou, Jiangsu 215123, China. §

School of Electronic and Optical Engineering, Nanjing University of Science and Technology,

Nanjing, Jiangsu 210094, China.

*†

Email: [email protected]

*‡

Email: [email protected]

*§

Email: [email protected] 1 ACS Paragon Plus Environment


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ABSTRACT Ultrafast transient absorption (TA) spectroscopy was employed to investigate the thermal annealing effect on the charge transfer (CT) in bulk heterojunction (BHJ) all-polymer solar cells (all-PSCs) utilizing an n-type polymer P(NDI2OD-T2) (Polyera, N2200) as acceptor and a low bandgap polymer PBPT as donor. The CT generates hole polarons residing in the PBPT and electron polarons belonging to N2200, manifested in the TA spectra of the BHJ films as the long-lived absorption peak centered at ~850 nm. The CT is most efficient in the film annealed at 160 oC and its efficiency declines monotonically when enhancing or reducing the annealing temperature, displaying a positive correlation with the power conversion efficiency (PCE) of the corresponding solar cell devices. This correlation is analyzed in terms of the crystallinity and phase separation, which are the key factors determining the performance of all-PSCs. Our results can provide a valuable guidance for the fabrication of BHJ all-PSCs to improve their PCE.

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1. INTRODUCTION

As one of the third generation photovoltaics technologies, solution-processed bulk heterojunction (BHJ) organic photovoltaics (OPV) have been developed dramatically during the past several years. Solar cell devices consisting of narrow bandgap polymers as electron donor and fullerene derivatives as electron acceptor have been demonstrated to possess the power conversion efficiency (PCE) of 10%-12%.1-4 Recently, BHJ all-polymer solar cells (all-PSCs) utilizing a p-type polymer as donor and an n-type polymer as acceptor have attracted much attention because they possess many advantages over the polymer/fullerene solar cells, such as low manufacturing cost, and flexible molecular design for fine tuning of the electronic, optical, and morphological properties.5, 6 However, the PCE of the BHJ all-PSCs still lag behind the conventional polymer/fullerene based solar cells.7, 8 Hence, vigorous efforts have been dedicated to exploit non-fullerene electron acceptors materials. Among the emergent n-type conjugated polymer acceptors, the co-polymer of nanphthalene diimide-bithiophene (N2200) has gained significant interests because of its high electron mobility and affinity, broad light absorption, and excellent thermal stability.9, 10

Since the first report of the BHJ all-PSCs based on the N2200 acceptor blended with the poly(3-hexylthiophene) (P3HT),11 the PCE of the polymer/N2200 all-PSCs has been steadily enhanced up to 8.27% by selecting appropriate donor polymers combined with the molecular structure modification, side-chain engineering, and thermal annealing treatment.12-15 Actually, the thermal annealing has been widely adopted in fabricating the conventional BHJ solar cells to 3 ACS Paragon Plus Environment


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optimize their performances, because it can, on the one hand, increase the polymer’s crystallinity, diminishing the body and interface defects, and on the other hand, improve the morphology in nanoscale and promote the contact between the polymer blends and electrodes thereby facilitating the charge transportation and collection.16 Recently, some groups have devoted to studying the intrinsic mechanisms on how thermal annealing affects the all-PSCs device performance.17-20 In these studies, the main attention was paid to the characterizations of phase separation, morphology, crystallinity, and parameters of device performance, whereas no study has revealed the correlation from the perspective of the ultrafast interfacial charge transfer (CT) that essentially determines the free carriers generation critical to the PCE.

In this paper, the ultrafast transient absorption (TA) spectroscopy was performed to characterize the CT in the BHJ blend films composed of a low bandgap p-type co-polymer of benzo[1,2-b:4,5-b’]dithiophene (BDT) and thiadiazolo[3,4-c]pyridine (PyTZ) (PBPT) as donor21 and the N2200 as acceptor, with their molecular structures shown in Figure 1a. The alignment of the energy levels allows the dissociation of photo-generated excitons by means of CT at the interface of PBPT and N2200, and the PCE of 4.30% was achieved under the condition of 160 o

C thermal annealing treatment. In the ultrafast TA measurements, ultrashort pump pulse and

time-delayed probe pulse were used to measure the transmission change (∆T/T), i.e., the differential transmission between the steady state (pump off) and the excited state (pump on), which embodies the depletion of the ground state and the filling of the excited states. We extracted from the ∆T/T spectra the long-lived photoinduced absorption (PA) signals induced by 4 ACS Paragon Plus Environment

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the free charge carriers generated from the CT. From the comparison of these PA signals in the PBPT/N2200 blend films under different annealing conditions, we can analyze the correlation of the CT with the PCE to provide deep insights on the impact of the annealing dependent crystallinity and phase separation on the overall device performances.

2. EXPERIMENTAL SECTION

2.1 Sample Preparation. Polymer PBPT and N2200 was prepared according to our previously report.8,

21

Glass

substrates with indium tin oxide (ITO)-coated were cleaned by ultrasonic in acetone, detergent, isopropyl alcohol, and acetone sequentially, with each step for 30 minutes. The dried substrates were treated with UV-ozone for 30 min. Next, poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT: PSS) solution was spin-coated on the top of ITO substrates at a rate of 4000 rpm for 40 s, and then annealed at 140 oC for 10 min. Blending of active layer solution which dissolved in chloroform were then spin-coated on the top of PEDOT: PSS with a rate of 3000 rpm for 40 s in a Nitrogen filled glove box. The total concentration of blend solutions was 10 mg mL−1. Next, the active layers were thermal annealed for 10 min at different temperature, from 80 o

C to 240 oC. To make the device, 0.6 nm thick Lithium fluoride (LiF) with 0.1 A s-1 and 80 nm

thick aluminum (Al) electrode with 1 A s-1 were thermal evaporated upon the active layer of 7.25 mm2 at a pressure nearly 1.0×10-7 mbar through a shadow mask.

2.2 Device Characterization and Sample Characterization. 5 ACS Paragon Plus Environment


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The J-V characteristics of the devices were measured with a Kheithey 2400 (I−V) digital source meter under simulated AM 1.5G solar irradiation at 100 mW cm-2 (Newport, Class AAA solar simulator, 94023A-U). The light intensity was calibrated by a certified Oriel Reference Cell (91150V) and verified with a NREL calibrated Hamamatsu S1787-04 diode. The absorption spectra were recorded on a Perkin Elmer model Lambda 750. TEM images were obtained using the Tecnai G2 F20 S-Twin Transmission Electron Microscope. The charge carrier mobility was measured by the space charge limited current (SCLC) method with a structure of ITO/ZnO/Blend/LiF/Al (electron-only device) for the electron mobility measurement.

2.3 Ultrafast TA and Quasi-steady state absorption (QSA) spectroscopies.

All the absorption spectroscopy measurements were conducted in an optical cryostat under vacuum at room temperature. For ultrafast TA spectroscopy, the laser source was a Ti: Sapphire amplifier laser with the central wavelength of 800 nm, the pulse width of ~120 fs, and the repetition rate of 1 kHz. We used the pump pulses at 400 nm, which were obtained through doubling the amplifier’s fundamental output with a beta barium borate (BBO) crystal. The pump beam was modulated by a mechanical chopper at ~320 Hz and focused on the sample with a spot diameter of ~3 mm. The fundamental 800 nm light was focused onto a sapphire plate to generate the supercontinuum white light, which passed though the different color filters with a 10 nm bandwidth to serve as the probe pulses in the range of 500-1000 nm. The pump and probe beam were spatially overlapped on the sample with the spot size of the pump beam slightly larger than the probe beam, and the probe light has much smaller energy density than the pump beam. The 6 ACS Paragon Plus Environment

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transmitted probe beam was detected by a silicon photodiode connected to a lock-in amplifier. Because sample replacement may cause the shift of the actual overlap position of pump and probe spot on the sample, we determine the time zero from the rising point in the curve of the transient transmission signal as a function of the time delay. For QSA spectroscopy measurements, we used a semiconductor laser with the wavelength of 447 nm for the pump and a Tungsten halogen lamp in the range of 550-1150 nm for the probe. The wavelength of transmitted probe beam was selected by a monochrometer, and the transmission variation (∆T), induced by the modulation of the pump beam, was measured by a silicon photodetector in combination of a lock-in amplifier. A long pass filter (>500 nm) was placed before the monochrometer to eliminate the influence of the stray light of the pump beam. The system was also used for measuring the PL spectra with the continuous wave pump light at the wavelength of 447 nm.

3. RESULTS AND DISCUSSION

Figure 1b displays the absorption spectra of the neat PBPT, N2200 films, and their blend film (as cast, D/A weight ratio=2/1). The PBPT has a broad absorption in range of 250-800 nm, and the absorption of N2200 is mainly in the range of 300-450 nm and 550-850 nm. The blend film exhibits the absorption as being the superposition of both the neat PBPT and pristine N2200, so we can see that the two absorption peaks centered at 675 nm and 730 nm contributed mainly from the PBPT are somewhat broadened because of their overlap with the absorption peak of the N2200 centered at 710 nm. 7 ACS Paragon Plus Environment


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Figure 1. (a) Molecular structure of PBPT and N2200 polymers; (b) Absorption, and (c) PL spectra of the pristine PBPT film, N2200 film, and the blend PBPT/N2200 (as cast) film with weight ratio of 2:1. The inset in (c) shows the energy levels and band alignment of PBPT and N2200.

The alignment of the energy levels in the blend film of PBPT and N2200 forms the type-II energy alignment22-24, as shown in the inset of Figure 1c, allowing electron transfer from the lowest unoccupied molecular orbit (LUMO) of PBPT to that of N2200, and holes transfer from the highest occupied molecular orbit (HOMO) of N2200 to that of PBPT. To examine the charge transfer, we first performed photoluminescence (PL) measurements of the neat PBPT, N2200, and their blend film (D/A weight ratio=2/1) without thermal annealing. The results shown in Figure 1c indicate that the PL of the neat PBPT is much stronger than that of the neat N2200, and 8 ACS Paragon Plus Environment

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the PL strength of the blend film is about one order in magnitude weaker than that of the pristine PBPT. This enormous PL quench implies the effective charge transfer at the interface of PBPT and N2200.25, 26

We then performed the ultrafast TA spectroscopy measurements in the neat PBPT, N2200, and the blend films (as cast) to study the interface charge transfer dynamics. Figure 2a-c shows the measured ∆T/T spectra in these films, and Figure 2e illustrates the optical transition model in which the pump light generates the singlet excitons followed by the charge transfer process forming positively charged polarons in PBPT/N2200 blend film.27-30 For the pristine PBPT, the photoinduced bleaching (PB) signals appear in the range of 550-800 nm with two peaks around 650 nm and 750 nm, which coincide with the wavelengths of the two absorption peaks shown in Figure 1b. This clearly indicates that the PB signals stem from the depletion of the ground state and/or the filling of the excited state by the photoinduced singlet excitons.31-33 These excitons can also induce extra absorption of the incident photons,23,24 thus reducing the probe transmission to form transient PA signals, as observed in the range of 500-550 nm and 800-1000 nm. The singlet excitons recombine quickly so that the PA signals decay to nearly zero within the delay time of 200 ps. However, in addition to the fast-decayed PB signals within 200 ps, we note a small PB component persisting longer than 500 ps. This long-lived PB signal may be originated from the formation of triplet excitons (T1) via the intersystem crossing (Isc) from the singlet excitons.11, 32-36



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Figure 2. Differential transmission spectra of (a) a neat PBPT film, (b) N2200 film, and (c) a blend PBPT/N2200 film (as cast; 2/1, nominal weight ratio) at different time delays between the pump (~70 µJ cm-2) and the probe pulses. (d) QSA spectroscopy of the pristine PBPT film (black 10 ACS Paragon Plus Environment

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line), N2200 film (red line), and PC60BM film (blue line), and the blend PBPT/N2200 film (dark cyan, as cast, 2/1, nominal weight ratio), and PBPT/PCBM film (magenta, as cast, 2/1, nominal weight ratio). (e) The schematic diagram of optical transitions and charge transfer after photoexcitation in PBPT/N2200 blend film. HOMO (LUMO) is the highest (lowest) occupied (unoccupied) molecular orbital in the charge manifold; Isc represents the intersystem crossing between singlet exciton state and triplet exciton state (T1).

Similar to the PBPT, the ∆T/T spectra of the pure N2200 also show PB signals in the range nearly coinciding with the absorption peak wavelengths, and PA signals in the shorter and longer wavelength range (500-600 nm and 830-1000 nm), which are resulted from the ground state bleaching and extra absorption by the excitons, respectively. In addition, a weak long-lived PB signal emerges in the range of 650-900 nm due to the formation of triplet excitons.

The ∆T/T spectra in the blend film have distinct features from those in the pristine PBPT and N2200. Though the PB signals in the blend film appear in a similar range of 600-750 nm, they have a much larger component with long lifetime over 500 ps compared to either the neat PBPT or N2200 film. Moreover, the PA signals show a large long-lived component which is negligible in the neat films. The emergent long-lived PB and PA signals in the blend film must arise from the free charge carriers generated by the interfacial CT. We believe that the PA peak around 850 nm is due to the charge polarons because the polymer polarons typically induce absorption at the wavelength slightly red-shifted from the band edge.31, 32, 37, 38 This attribution was supported by the QSA measurements which enable us to reveal the absorption peak induced 11 ACS Paragon Plus Environment


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by the polarons with long lifetime up to millisecond.32, 39 Figure 2d show the measured QSA spectra in the neat PBPT, N2200, and their blend film, and for comparison, the results from the fullerene (PC60BM) and PBPT/PC60BM blend films are also included. Here, we can clearly identify the PA in the range of 800-1000 nm in both PBPT/N2200 and PBPT/PC60BM blend films, whereas no such absorption appears in the neat films. Actually, the ultrafast TA measurements of the PBPT/PC60BM film also revealed a long-lived PA within this wavelength range (Figure S1, Supporting Information), further confirming its origin from the polarons. The other PA peak at ~1110 nm in the PBPT/PC60BM may be attributed to the anion absorption of the fullerene.40 To directly identifying the polaron absorption in PBPT chains, we conducted the doping induced absorption (DIA) measurements,41 with the results shown in Figure S2. We note an apparent absorption enhancement in a broad range of 800 nm-1000 nm due to the formation of hole polarons after doping the pristine PBPT film using Iodine vapor. The enhanced absorption in DIA spectrum coincides with the long-lived PA in ∆T/T spectra of the PBPT/N2200 and PBPT/PC60BM blend films for both TA and QSA measurements. Additionally, Mario Caironi et al had revealed in pristine N2200 a very sharp charge polaronic absorption peak located at 1.48 eV (~837 nm) based on the charge-modulation spectroscopy.42 Thus, we can conclude that the long-lived PA with peak at ~850 nm in PBPT/N2200 is due to the joint contribution of hole polarons in PBPT and electron polarons in N2200 as a result of the effective interfacial charge transfer. Apart from the large PA signals, we also note that the PB signals in the QSA spectra are much stronger in the blend films than in the neat films, also suggesting


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abundant free carriers resulting from the effective charge transfer.

Figure 3a compares ∆T/T dynamics at 850 nm for the PBPT, N2200, PBPT/N2200, and PBPT/PC60BM blend films excited at a sufficiently low pump fluence (~7 μJ cm-2) where the influence of exciton-exciton, exciton-charge annihilation, and bimolecular charge recombination on the kinetics are suppressed (Figure S3, Supporting Information). These ∆T/T curves are normalized at 0.6 ps when the PA signals in the neat N2200 and PBPT reach the peak value. The PA signal in the PBPT/N2200 blend film decays much slower than that in the neat films within the whole detected time range. This slower decay is because of the compensation of the decreased PA due to exciton annihilation by the increased PA arising from the CT induced polarons which have long lifetime. Moreover, an apparent rising PA component can also be identified within 40 ps in the blend film, which indicates that during this time range, the CT is so effective that the increased polaron-induced PA is overwhelming compared to the decreased PA caused by geminate exciton recombination. Interestingly, PA dynamics at 850 nm in the PBPT/PC60BM blend film (PCE in the corresponding device of more than 5%21) is very similar to that in the PBPT/N2200 blend film. This comparison reveals that the CT is effective in both PBPT/N2200 and PBPT/PC60BM films, but it is not sufficient to judge which one has better CT efficiency since the PBPT/N2200 involves both electron and hole transfer whereas the electron transfer is the major source for charge generation in PBPT/PC60BM. In addition, the directly photo-excited excitons in N2200 have large PA contribution at 850 nm, whereas PC60BM has very weak absorption, thus contributing very small transient signals without CT. Furthermore, 13 ACS Paragon Plus Environment


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the CT induced electron polaron in the N2200 and PC60BM may also have different contributions to the PA at 850 nm.

Figure 3. (a) The normalized decay dynamics of the transient differential transmissions probed at 850 nm in the pristine PBPT film (black line), N2200 film (red line), the blend PBPT/N2200 film (blue line, as cast, nominal weight ratio of 2:1) and the blend PBPT/PC60BM film (magenta line, as cast, 2/1, nominal weight ratio). (b) The normalized ∆T/T dynamic probed at 850 nm for the PBPT/N2200 blend films of as cast and annealed at different temperature. The pump fluence used in (a) and (b) is ~7 µJ cm-2. (c) The photovoltaic parameters, including the power conversation efficiency (PCE), shunt resistance (Rsh) in unit of kΩ cm2, series resistance (Rse) in 14 ACS Paragon Plus Environment

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unit of Ω cm2, fill factor (FF), short-circuit current density (Jsc) in unit of mA cm-2, and open-circuit voltage (Voc) in unit of V, of the PBPT/N2200 blend films of as cast and annealed at different temperature.

The PBPT/N2200 blend films were then annealed at different temperatures in order to investigate the thermal annealing effect on the interfacial CT. The PA dynamics probed at 850 nm for these annealed films under pump fluence of ~7 μJ cm-2 are shown in Figure 3b. These PA dynamics are also normalized at 0.6 ps, the same time delay used for normalization as in Figure 3a. Under such normalization, the initial rising PA curves up to 0.6 ps for all blend films are well overlapped. However, we can see an additional rising PA component after 0.6 ps due to the formation of polarons by CT, which varies for different blend films. The rising component in the film annealed at 160 oC shows the longest duration and largest amplitude, and consequently this film has the largest long-lived PA component beyond 200 ps. The long-lived component gets smaller for films with increasing or decreasing annealing temperature (AT). These results thus indicate that the charge transfer is most effective in the film annealed at 160 oC and the transfer efficiency decreases for films with increasing or decreasing AT. For higher pump fluence of ~70 µJ cm-2, the exciton-excition, exciton-charge annihilation, and bimolecular charge recombination are facilitated, so the charge transfer is suppressed and the PA rising component greatly diminishes or even disappears (Figure S4, Supporting Information). Nevertheless, the long lived PA and PB components in these blend films display the same trend with AT as those in Figure 3b. Notably, the difference between these long lived components becomes more pronounced for 15 ACS Paragon Plus Environment


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the higher pump fluence. This may be because for less effective CT, more exciton-exciton recombination events can occur before the exciton can dissociate via CT, thus resulting in even fewer CT induced polaron states.

We examined the performances of the solar cell devices based on these annealed films. Figure 3c shows the photovoltaic parameters including the power conversion efficiency (PCE), short-circuit current density (Jsc), open-circuit voltage (Voc), shunt resistance (Rsh), series resistance (Rse), and fill factor (FF). Interestingly, we can see that the device composed of the blend film annealed at 160 oC has the best PCE, and the PCE reduces gradually with decreasing or increasing AT, displaying an identical variation tendency as that of the interfacial CT efficiency with AT. This intimate positive correlation reveals that the CT though the interface plays the prominent role in the performance of the BHJ all-PSCs.

Figure 4. (a) Normalized PL spectra, and (b) Electron mobility (ߤ௘ ) of the PBPT/N2200 blend films (2/1, nominal weight ratio) of as cast and annealed at different temperature. The PL spectra were measured at 80 K with the pump wavelength of 447 nm. 16 ACS Paragon Plus Environment

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To understand the AT dependence of the CT efficiency and its correlations with the PCE and other photovoltaic parameters, we performed photoluminescence (PL), electron mobility, and transmission electron microscopy (TEM) measurements to obtain the crystallinity, phase separation and morphology information of the blend films. Figure 4a shows that the two PL peaks, which locate at ~850 nm (0-0 peak) and ~930 nm (0-1 peak, the phonon replica of the 0-0 peak), coincide with the two absorption peaks of PBPT but have stokes shifts. These two peaks arise from PBPT because the PL from N2200 is negligible in the blend film. The ratio of the 0-1 and 0-0 peak intensities is highest for the film annealed at 200 oC, indicating the best crystallinity of PBPT at this AT because adding disorder allows the 0-0 emission which is otherwise forbidden by the symmetry.43 The N2200 was shown to have the best crystallinity at the AT of ~200 oC by Kim et al19. We note that the electron mobility of blend films increases progressively with the increasing AT up to 200 oC, and it decreases to some degree when annealed at 240 oC, as shown in Figure 4b, in agreement with the mobility tendency in our previous report [18]. This tendency is actually consistent with the best film crystallinity at AT of ~200 oC. The better crystallinity is indicative of the higher molecular packing order, which may reduce the Rse of the material, as can be seen in Figure 3c. Moreover, it will also lead to the reduction of the defect related exciton recombination, and thus benefits the CT. However, for AT at 200 oC, the phase separation becomes stronger and the interfacial areas for CT are diminished, as can be roughly judged from the TEM images shown in Figure 5. The observation of larger crystalline domain size of the N2200 film annealed at 200 oC compared to the films with lower or higher AT was



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actually reported in Ref. [19]. This result may explain the suppression of the CT in the blend film annealed at 200 oC compared to the film annealed at 160 oC. The overall CT efficiency is actually balanced by the crystallinity and interface areas. In addition, the molecular orientation of the polymer is also important for the charge transfer and transport. For AT close to 250 oC, the face on N2200 molecular tends to reorient in edge on stacking,44,45 which may account for the significant decrease of CT observed in the 240 oC annealed film to a level even lower than that in the as cast film with the lowest crystallinity. Based on such observed AT dependent CT efficiency and crystallinity, one can understand the trend of Jsc in Figure 3c which shows the largest value in the film annealed at 160 oC. The suppressed CT also leads to the increased probability of the excitons’ geminate recombination in films with good crystallinity, and consequently enhanced PL intensity, as can be seen in the films annealed at 200 oC and 240 oC shown in Figure S5 (Supporting Information). The enhanced exciton recombination results in the extra loss of photocurrent, thus it may account for the decreased Rsh for the devices composed of these two films. Because of these factors, it is reasonable to expect the highest PCE in the device composed of the film annealed at 160 oC.


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Figure 5. The TEM images of the PBPT/N2200 blend films (2/1, nominal weight ratio) of as cast and annealed at different temperature.

4. CONCLUSIONS

In summary, we have conducted a systematic investigation of the photo-generated CT dynamics in the BHJ blend films composed of the PBPT and N2200 under different annealing conditions by using the ultrafast transient absorption spectroscopy. The blend films possess long-lived hole polarons as a result of the interfacial CT under light excitation, which are absent in the pristine films of both PBPT and N2200. The generally consistent variation tendency of the CT and device performance with the AT reveals that controlling the interfacial CT with appropriate polymer crystallinity and phase separation have a decisive influence on the PCE in 19 ACS Paragon Plus Environment


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the BHJ all-PSCs. Our results can provide a valuable guidance for the fabrication of the active layers in the BHJ all-PSCs.

ASSOCIATED CONTENT

Supporting Information The Supporting Information is available free of charge Doping induced absorption of the pristine PBPT. Ultrafast TA spectra of the PBPT/PC60BM film. Ultrafast TA dynamics for the PBPT/N2200 film at different pump fluence. Ultrafast TA dynamics for the PBPT/N2200 films with different AT at high pump fluence. PL spectra of the PBPT/N2200 blend films.

AUTHOR INFORMATION

Corresponding Authors *†

Haibin Zhao; *‡Wanli Ma; *§Chuanxiang Sheng

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS

This work was supported by National Key Basic Research Program of China (No. 2015CB921403), National Key Research Program of China (No. 2016YFA0300703), and the National Natural Science Foundation of China (Grants No. 51371052, No. 61674111).


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REFERENCES

1.

He, Z.; Xiao, B.; Liu, F.; Wu, H.; Yang, Y.; Xiao, S.; Wang, C.; Russell, T. P.; Cao, Y.,

Single-Junction Polymer Solar Cells With High Efficiency and Photovoltage. Nat. Photon. 2015, 9, 174-179. 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.

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, 5293-5293. 4.

Kan, B.; Zhang, Q.; Li, M.; Wan, X.; Ni, W.; Long, G.; Wang, Y.; Yang, X.; Feng, H.; Chen,

Y., Solution-Processed Organic Solar Cells Based on Dialkylthiol-Substituted Benzodithiophene Unit with Efficiency Near 10%. J. Am. Chem. Soc. 2014, 136, 15529-15532. 5.

Facchetti, A., Polymer Donor–Polymer Acceptor (All-Polymer) Solar Cells. Mater. Today

2013, 16, 123–132. 6.

Benten, H.; Mori, D.; Ohkita, H.; Ito, S., Recent Research Progress of Polymer

Donor/Polymer Acceptor Blend Solar Cells. J. Mater. Chem. A 2016, 4, 5340-5365. 7.

Gao, L.; Zhang, Z. G.; Xue, L.; Min, J.; Zhang, J.; Wei, Z.; Li, Y., All-Polymer Solar Cells

Based on Absorption-Complementary Polymer Donor and Acceptor with High Power Conversion Efficiency of 8.27%. Adv. Mater. 2016, 28, 1884-1890. 8.

Yuan, J.; Ma, W., High Efficiency All-Polymer Solar Cells Realized By the Synergistic



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 22 of 28

Effect Between the Polymer Side-Chain Structure and Solvent Additive. J. Mater. Chem. A 2015, 3, 7077-7085. 9.

Yan, H.; Chen, Z.; Zheng, Y.; Newman, C.; Quinn, J. R.; Dotz, F.; Kastler, M.; Facchetti, A.,

A High-Mobility Electron-Transporting Polymer for Printed Transistors. Nature 2009, 457, 679-686. 10. Tremel, K.; Fischer, F. S. U.; Kayunkid, N.; Pietro, R. D.; Tkachov, R.; Kiriy, A.; Neher, D.; Ludwigs, S.; Brinkmann, M., Charge Transport Anisotropy in Highly Oriented Thin Films of the Acceptor Polymer P(NDI2OD-T2). Adv. Energy Mater. 2014, 4, 1301659. 11. Moore, J. R.; Albert-Seifried, S.; Rao, A.; Massip, S.; Watts, B.; Morgan, D. J.; Friend, R. H.; McNeill, C. R.; Sirringhaus, H., Polymer Blend Solar Cells Based on a High-Mobility Naphthalenediimide-Based Polymer Acceptor: Device Physics, Photophysics and Morphology. Adv. Energy Mater. 2011, 1, 230-240. 12. Mori, D.; Benten, H.; Okada, I.; Ohkita, H.; Ito, S., Highly Efficient Charge-Carrier Generation and Collection in Polymer/Polymer Blend Solar Cells with a Power Conversion Efficiency of 5.7%. Energy Environ. Sci. 2014, 7, 2939. 13. Schubert, M.; Dolfen, D.; Frisch, J.; Roland, S.; Steyrleuthner, R.; Stiller, B.; Chen, Z.; Scherf, U.; Koch, N.; Facchetti, A.; et al., Influence of Aggregation on the Performance of All-Polymer Solar Cells Containing Low-Bandgap Naphthalenediimide Copolymers. Adv. Energy Mater. 2012, 2, 369-380. 14. Jung, J. W.; Jo, J. W.; Chueh, C. C.; Liu, F.; Jo, W. H.; Russell, T. P.; Jen, A. K.,


Page 23 of 28

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


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. 15. Shi, S.; Yuan, J.; Ding, G.; Ford, M.; Lu, K.; Shi, G.; Sun, J.; Ling, X.; Li, Y.; Ma, W., Improved All‐ Polymer Solar Cell Performance by Using Matched Polymer Acceptor. Adv. Funct. Mater. 2016, 26, 5669-5678. 16. Ma, W.; Yang, C.; Gong, X.; Lee, K.; Heeger, A. J., Thermally Stable, Efficient Polymer Solar Cells with Nanoscale Control of the Interpenetrating Network Morphology. Adv. Funct. Mater. 2005, 15, 1617-1622. 17. Murari, N. M.; Crane, M. J.; Earmme, T.; Hwang, Y.-J.; Jenekhe, S. A., Annealing Temperature Dependence of the Efficiency and Vertical Phase Segregation of Polymer/Polymer Bulk Heterojunction Photovoltaic Cells. Appl. Phys. Lett. 2014, 104, 223906. 18. Ding, G.; Yuan, J.; Huang, X.; Liu, Z.; Shi, G.; Shi, S.; Ding, J.; Wang, H.-Q.; Ma, W., Efficient

All

Polymer

Solar

Cells

Employing

Donor

Polymer

Based

on

Benzo[1,2-b:4,5-b’]dithiophene Unit. AIP Adv. 2015, 5, 117126. 19. Kim, Y. J.; Park, C. E., The Impact of P(NDI2OD-T2) Crystalline Domains on the Open-Circuit Voltage of Bilayer All-Polymer Solar Cells with an Inverted Configuration. APL Mater. 2015, 3, 126105. 20. Kim, Y. J.; Chung, D. S.; Park, C. E., Highly Thermally Stable Non-Fullerene Organic Solar Cells: p-DTS(FBTTh2)2:P(NDI2OD-T2) Bulk Heterojunction. Nano Energy 2015, 15, 343-352.



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 24 of 28

21. Yuan, J.; Huang, X.; Dong, H.; Lu, J.; Yang, T.; Li, Y.; Gallagher, A.; Ma, W., Structure, Band Gap and Energy Level Modulations for Obtaining Efficient Materials in Inverted Polymer Solar Cells. Org. Electron. 2013, 14, 635-643. 22. Lo, S. S.; Mirkovic, T.; Chuang, C. H.; Burda, C.; Scholes, G. D., Emergent Properties Resulting from Type-II Band Alignment in Semiconductor Nanoheterostructures. Adv. Mater. 2011, 23, 180-197. 23. Marschall, R., Semiconductor Composites: Strategies for Enhancing Charge Carrier Separation to Improve Photocatalytic Activity. Adv. Funct. Mater. 2014, 24, 2421-2440. 24. Li, H.; Zhou, Y.; Tu, W.; Ye, J.; Zou, Z., State-of-the-Art Progress in Diverse Heterostructured Photocatalysts toward Promoting Photocatalytic Performance. Adv. Funct. Mater. 2015, 25, 998-1013. 25. Haugeneder, A.; Neges, M.; Kallinger, C.; Spirkl, W.; Lemmer, U.; Feldmann, J.; Scherf, U.; Harth, E.; Gügel, A.; Müllen, K., Exciton Diffusion and Dissociation in Conjugated Polymer/Fullerene Blends and Heterostructures. Phys. Rev. B 1999, 59, 15346-15351. 26. Xing, G.; Mathews, N.; Sun, S.; Lim, S. S.; Lam, Y. M.; Gratzel, M.; Mhaisalkar, S.; Sum, T. C., Long-range Balanced Electron- and Hole-Transport Lengths in Organic-Inorganic CH3NH3PbI3. Science 2013, 342, 344-347. 27. Frolov, S. V.; Bao, Z.; Wohlgenannt, M.; Vardeny, Z. V., Ultrafast Spectroscopy of Even-Parity States in pi-Conjugated Polymers. Phys. Rev. Lett. 2000, 85, 2196-2199. 28. Frolov, S. V.; Bao, Z.; Wohlgenannt, M.; Vardeny, Z. V., Excited-State Relaxation in


Page 25 of 28

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


π-Conjugated Polymers. Phys. Rev. B 2002, 65, 205209. 29. Sheng, C. X.; Tong, M.; Singh, S.; Vardeny, Z. V., Experimental Determination of the Charge/Neutral Branching Ratio η in the Photoexcitation of π -Conjugated Polymers by Broadband Ultrafast Spectroscopy. Phys. Rev. B 2007, 75, 085206. 30. Nuzzo, D. D.; Aguirre, A.; Shahid, M.; Gevaerts, V. S.; Meskers, S. C. J.; Janssen, R. A. J., Improved Film Morphology Reduces Charge Carrier Recombination into the Triplet Excited State in a Small Bandgap Polymer-Fullerene Photovoltaic Cell. Adv. Mater. 2010, 22, 4321-4324. 31. Hodgkiss, J. M.; Campbell, A. R.; Marsh, R. A.; Rao, A.; Albert-Seifried, S.; Friend, R. H., Subnanosecond Geminate Charge Recombination in Polymer-Polymer Photovoltaic Devices. Phys. Rev. Lett. 2010, 104, 177701. 32. Etzold, F.; Howard, I. A.; Mauer, R.; Meister, M.; Kim, T. D.; Lee, K. S.; Baek, N. S.; Laquai, F., Ultrafast Exciton Dissociation Followed by Nongeminate Charge Recombination in PCDTBT:PCBM Photovoltaic Blends. J. Am. Chem. Soc. 2011, 133, 9469-9479. 33. Deschler, F.; De Sio, A.; von Hauff, E.; Kutka, P.; Sauermann, T.; Egelhaaf, H.-J.; Hauch, J.; Da Como, E., The Effect of Ageing on Exciton Dynamics, Charge Separation, and Recombination in P3HT/PCBM Photovoltaic Blends. Adv. Funct. Mater. 2012, 22, 1461-1469. 34. Schubert, M.; Collins, B. A.; Mangold, H.; Howard, I. A.; Schindler, W.; Vandewal, K.; Roland, S.; Behrends, J.; Kraffert, F.; Steyrleuthner, R.; et al., Correlated Donor/Acceptor Crystal Orientation Controls Photocurrent Generation in All-Polymer Solar Cells. Adv. Funct. Mater. 2014, 24, 4068-4081.



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 26 of 28

35. Inoue, M.; Serevičius, T.; Nakanotani, H.; Yoshida, K.; Matsushima, T.; Juršėnas, S.; Adachi, C., Effect of Reverse Intersystem Crossing Rate to Suppress Efficiency Roll-Off in Organic Light-Emitting Diodes with Thermally Activated Delayed Fluorescence Emitters. Chem. Phys. Lett. 2016, 644, 62-67. 36. Guo, J.; Ohkita, H.; Yokoya, S.; Benten, H.; Ito, S., Bimodal Polarons and Hole transport in Poly(3-hexylthiophene):Fullerene Blend Films. J. Am. Chem. Soc. 2010, 132, 9631-9637. 37. Sheng, C. X.; Singh, S.; Gambetta, A.; Drori, T.; Tong, M.; Tretiak, S.; Vardeny, Z. V., Ultrafast Intersystem-Crossing in Platinum Containing π-Conjugated Polymers with Tunable Spin-Orbit Coupling. Sci. Rep. 2013, 3, 2653. 38. Clarke, T. M.; Ballantyne, A. M.; Tierney, S.; Heeney, M.; Duffy, W.; Mcculloch, I.; Nelson, J.; Durrant, J. R., Charge Photogeneration in Low Band Gap Polyselenophene/Fullerene Blend Films. J. Phys.Chem.C 2010, 114, 8068-8075. 39. Howard, I. A.; Mauer, R.; Meister, M.; Laquai, F., Effect of Morphology on Ultrafast Free Carrier Generation in Polythiophene:Fullerene Organic Solar Cells. J. Am. Chem. Soc. 2010, 132, 14866-14876. 40. Schlenker, C. W.; Chen, K.-S.; Yip, H.-L.; Li, C.-Z.; Bradshaw, L. R.; Ochsenbein, S. T.; Ding, F.; Li, X. S.; Gamelin, D. R.; Jen, A. K. Y.; et al., Polymer Triplet Energy Levels Need Not Limit Photocurrent Collection in Organic Solar Cells. J. Am. Chem. Soc. 2012, 134, 19661-19668. 41. Basel, T.; Huynh, U.; Zheng, T.; Xu, T.; Yu, L.; Vardeny, Z. V., Optical, Electrical, and


Page 27 of 28

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


Magnetic Studies of Organic Solar Cells Based on Low Bandgap Copolymer with Spin ½ Radical Additives. Adv. Funct. Mater. 2015, 25, 1895-1902. 42. Caironi, M.; Bird, M.; Fazzi, D.; Chen, Z.; Pietro, R. D.; Newman, C.; Facchetti, A.; Sirringhaus, H., Very Low Degree of Energetic Disorder as the Origin of High Mobility in an n‐ channel Polymer Semiconductor. Adv. Funct. Mater. 2011, 21, 3371-3381. 43. Spano, F. C.; Clark, J.; Silva, C.; Friend, R. H., Determining Exciton Coherence from the Photoluminescence Spectral Line Shape in Poly(3-hexylthiophene) Thin Films. J. Phys. Chem. C 2009, 130, 074904. 44. Rivnay, J.; Steyrleuthner, R.; Jimison, L. H.; Casadei, A.; Chen, Z.; Toney, M. F.; Facchetti, A.; Neher, D.; Salleo, A., Drastic Control of Texture in a High Performance n-Type Polymeric Semiconductor and Implications for Charge Transport. Macromolecules 2011, 44, 5246-5255. 45. Zhang, R.; Yang, H.; Zhou, K.; Zhang, J.; Yu, X.; Liu, J.; Han, Y., Molecular Orientation and Phase Separation by Controlling Chain Segment and Molecule Movement in P3HT/N2200 Blends. Macromolecules 2016, 49, 6987−6996.



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Table of Contents Graphic


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Thermal Annealing Effect on Ultrafast Charge Transfer in All-Polymer

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