Orienting the Microstructure Evolution of Copper Phthalocyanine as an

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Orienting Microstructure Evolution of Copper Phthalocyanine as Anode Interlayer in Inverted Polymer Solar Cells for High Performance Zhiqi Li, Chunyu Liu, Xinyuan Zhang, Shujun Li, Xulin Zhang, Jiaxin Guo, Wenbin Guo, Liu Zhang, and Shengping Ruan ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b04947 • Publication Date (Web): 24 Aug 2017 Downloaded from http://pubs.acs.org on August 25, 2017

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ACS Applied Materials & Interfaces

Orienting Microstructure Evolution of Copper Phthalocyanine as Anode Interlayer in Inverted Polymer Solar Cells for High Performance Zhiqi Li,1 Chunyu Liu,1 Xinyuan Zhang,1 Shujun Li,1 Xulin Zhang,1 Jiaxin Guo,1 Wenbin Guo, *1 Liu Zhang,*2 and Shengping Ruan1 1

State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, People’s Republic of China 2

College of Instrumentation & Electrical Engineering, Jilin University, 938 Ximinzhu Street, Changchun 130061, People’s Republic of China

ABSTRACT Recent advances in interfacial modification of inverted-type polymer solar cells (PSCs) have resulted from controlling the surface energy of cathode modified layer (TiO2 or ZnO) to enhance the short-circuit current (Jsc) or optimizing contact morphology of cathode (ITO or FTO) and active layer to increase the fill factors (FF). Herein, we report the performance enhancement of PSCs is achieved by containing donor macromolecule copper phthalocyanine (CuPc) as anode modification layer. Using the approach based on orienting microstructure evolution, uniformly dispersed island-shape CuPc spot accumulations are built on the top of PTB7:PC71BM blend film, leading to an efficiently spectrum absorption and photo-generated exciton split. The best power conversion efficiency of PSCs is increased up to 9.726 %. In addition to the enhanced light absorption, the tailored anode energy levels alignment and optimized boundary morphology by incorporating CuPc interlayer boost efficient charge extraction and suppress interfacial molecular recombination. These results demonstrate that surface morphology induction through molecular deposition is an effective method to improve the performance of PSCs, which reveals the potential implications of interlayer between organic active layer and buffer layer or electrode. KEYWORDS: Orienting Microstructure Evolution, Morphology Induction, Light Absorption, Charge Extraction, Power Conversion Efficiency 1.

INTRODUCTION Polymer solar cells (PSCs) have shown potential as an emerging photovoltaic technology to

harness solar energy compared to the traditional silicon devices because of the excellent properties in low-cost and large-area fabrication compatibility, as well as applications in flexibility, colourful, transparency, and light-weight devices.1-9 With the discovery of spontaneous phase separation of the 1

ACS Paragon Plus Environment


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bulk hetero-junction (BHJ) concept, efficient photo-induced electron transfer from the donor (conjugated polymer) to the acceptor (fullerene) makes the BHJ PSCs be one of the most intensively studied types in the field to date.10-12 Different from the single junction structure, the familiar BHJ architecture can form a self-assembling interpenetrating network between polymers (electron donors) and fullerene (electron acceptor) through simply blending two kinds of materials in organic solvents, thus the BHJ films can be produced by different coating techniques, including laboratory-scale spin coating and spray coating to large-scale manufacturing technologies (inkjet printing,13 doctor blading, gravure,14,15 slot-die coating,16 and flexographic printing17 etc.). Especially, the inverted-type sandwiched BHJ solar cells consisting of a polymer:fullerene hybrid active layer between a transparent metal-oxide cathode (ITO, FTO etc) and a metallic anode (Ag, Al etc) have became the most successful device structure in organic photovoltaic field.18-24 For the last several years, many significant accomplishments have been achieved with the purpose of improving the power-conversion efficiency (PCE) of inverted-type devices, and device performance has steadily improved. Several effective methods have also been developed to further optimize device performance for large-scale commercialization, such as the exploitation of new device structures,25 rational design of new materials (polymers or buffer layer),26,27 lateral and vertical morphology optimization of photo-active layer via processing methods or addition,28 tandem,29 molecular doping of photovoltaic layer30 or cathode buffer layer,31 and interfacial engineering.32 Among them, the study on interface engineering, which has been performed for a long time, is a key topic not only in surface chemistry but also device physics. For hierarchical multilayer structure, the contact resistance and the bulk conductivity between the functional layers determine the series resistance (Rs) of solar cells, which is one of the most critical factors in determining Jsc and FF.33,34 Understanding and controlling the interfacial modification are essential for improving the characteristics of PSCs. All kinds of experimental methods have been employed to improve the interface contact of different layer, including conductive polymer nanolayer35, self-assembled monolayer the permanent dipole moment,36 and these combined effect have achieved a very encouraging PCE.37-41 Nevertheless, the efforts on surface modification of inverted-type PSCs have mainly focused on cathode buffer layer and transparent metal-oxide cathode.42-45 Upon modifying anode electrode and anode buffer layer to perfect the contact and tune the energy bands of different layers are equally important. In this study, we report the reconstruction of anode buffer layer with a slow thermal 2


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evaporation-deposited donor macromolecule of copper phthalocyanine (CuPc) can effectively tailor the interfacial properties of PSCs. By controlling the evaporation rate of polymer to orient microstructure evolution, uniformly dispersed island-shape CuPc spot accumulations were built on the top of Poly{4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b :4,5-b ']dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl) carbonyl]thieno[3,4-b]thiophene-4,6-diyl} (PTB7):[6,6]-phenyl-C70-butyric acid methyl ester (PC71BM) vaporizing surface layer. This multifunctional CuPc layer acts as not only an anode modification layer but also a multiple energy donor and optical field spacer, thereby enabling to enhance light absorption and facilitate holes transport. Especially, this multifunctional system transcends traditional tandem or multi-blend architectures, ensuring multiple donors and acceptor with respective spectral responses to cooperatively work, resulting in significantly improved light-harvesting and photo-generated exciton. Our work represents a surprising new lead in orienting microstructures evolution for the development of interfacial modification in polymer optoelectronic devices. 2.

EXPERIMENTAL Firstly, TiO2 (synthesized based on our previous reports.46,47) thin film (40 nm) was spin-coated on

top of pre-cleaned ITO substrates. The active layer (100 nm) was then spin-coated from precursor solution on the top of TiO2 with 1,000 rpm for 60 s in a glove box. For the CuPc-based device, CuPc was thermally evaporated on the top of active layers in a glove box at a chamber pressure of ∼5.0×10−4 torr. To induce and control orienting microstructures evolution of CuPc film inside nano-pores on the active layer, the evaporation rate of CuPc was exactly controlled by adjusting the reactive temperature. Finally, a MoO3 (4 nm) and silver film (100 nm) were deposited on top of CuPc in turn. For comparison, the control devices without CuPc capping layer were also made using the same procedure. The detailed experimental and measurement were summarized in Supplementary Information. 3.

RESULTS AND DISCUSSION

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Figure 1 The inverted PSCs (a) without and (b) with CuPc modification layer; top surface of PTB7:PC71BM layer (c) without and (d) with island-shape CuPc spot accumulations; (e) J–V characteristics of the photovoltaic devices with CuPc thickness ranging from 0 to 15 nm, (f) IPCE spectra of control and optimized devices with CuPc thickness ranging from 0 to 15 nm. Table 1 The detailed device parameters of PSCs with various thickness of CuPc interlayer, including the best PCE, the average PCE, Voc, Jsc, FF, and series resistance. Rs (ohm/mm2)

CuPc thickness

PCE

PCE (average)

Voc

Jsc

FF

(nm)

(best) (%)

(%)

(V)

(mA/cm2)

(%)

0 (Control)

7.779

7.76± 0.06

0.801

16.043

60.58

17.31

3

8.307

8.28± 0.04

0.801

17.004

61.56

15.23

7

8.819

8.80± 0.02

0.802

17.628

62.36

14.37

9

9.726

9.72± 0.01

0.804

18.668

64.77

11.00

4


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15

8.892

8.88± 0.01

0.793

18.421

60.85

16.16

In this segment, we present the consequence of improved characteristic of PSCs by using CuPc modification layer, including current density versus voltage (J–V) characteristics, charge generation, separation and transport dynamics, nanoscale film morphology, and photophysics study of PTB7, PC71BM, and CuPc. The solar cells fabricated in this study have a simple structure that we has been employed

in

our

previous

(ITO)/TiO2/PTB7:PC71BM/MoO3/Ag

papers,

whose

(Figure

1a)

configuration

is

indium

for

reference

tin

oxide

devices

and

(ITO)/TiO2/PTB7:PC71BM/CuPc/MoO3/Ag (Figure 1b) for optimized devices. The current density versus voltage (J–V) curves of PTB7:PC71BM-devices with various thicknesses CuPc capping layer under one sun illumination are demonstrated in Figure 1e, and the detailed photovoltaic parameters of all devices are summarized in Table 1. The control devices without CuPc capping layer have a typical PCE of 7.779 % including a Voc of 0.8 V, a Jsc of 16.043 mA cm−2, and a FF of 60.58 %. The incorporation of a small thickness of CuPc film (3–9 nm) on the top of the host PTB7:PC71BM layer led to a great improvement in Jsc and FF. The device with a 3 nm thickness CuPc layer indicated a PCE of 8.307 %, including a Jsc of 17.004 mA cm-2, a Voc of 0.801 V, and a FF of 61.56 %. When the thickness of CuPc was increased to 7 nm, Jsc was improved to 17.628 mA cm−2, yielding a PCE of 8.819 %. After the thickness of CuPc was increased up to about 9 nm, the device exhibited the highest PCE of 9.726 %. The best optimized devices possessed a Jsc of 18.668 mA cm-2, a Voc of 0.804 V, and a FF of 64.77%, and the calculated average PCE value was 9.72 ± 0.01% (Table 1). Because this way provided a better solar cell performance than the reference device, it was used in the following measurements to unravel the mechanism of the increased Jsc and FF in the multilayer system. However, further increasing the thickness beyond 15 nm resulted in a decreased solar cells performance with inferior Jsc and FF, which is still higher than the value of reference device without CuPc interlayer. Moreover, the increase of Jsc generally originates from the enhancement of the incident photon-to-electron conversion efficiency (IPCE), and IPCE of the devices was measured and shown in Figure 1d. The IPCE spectra are consistent with the tendency of measured Jsc of the devices. Incorporation of 3 nm CuPc capping layer on the top of PTB7:PC71BM film resulted in a higher IPCE compared to reference devices. The improvement of IPCE intensity can be divided into two regions of 300–450 and 500–750 nm. Interestingly, when the thickness of CuPc layer is up to 7 nm, the devices exhibit the improved IPCE over the whole wavelength range with the typical spectral response of 370 5



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nm, 550 nm, and 750 nm. When the thickness of CuPc was about 9 nm, the device presented the highest IPCE, and the peak value of 0.83 locating in 520 nm is achieved compared to the value of 0.61 in 530 nm for reference devices. Further increasing the thickness beyond 15 nm resulted in a decreased IPCE accompanying a reduced device performance. Jsc values were calculated using the IPCE spectra, which were 15.42 mA/cm2, 16.63 mA/cm2, 17.09 mA/cm2, 18.18 mA/cm2, 17.96 mA/cm2, respectively for different devices. However, Voc of the optimized solar cells was pinned to the value of the PTB7:PC71BM host blend at all condition, which is attributed to the fact that Voc is mainly determined by the smallest difference between the highest occupied molecular orbital (HOMO) energy level of PTB7 and the lowest unoccupied molecular orbital (LUMO) energy level of PC71BM. The HOMO energy levels of PTB7 and CuPc are –5.15 eV and –5.2 eV, respectively. Generally, the thickness of CuPc film is less than 20 nm, which has little impact on the energy levels alignment and Voc remains the same.48-50

Figure 2 Tapping-mode AFM height image (5 µm× 5 µm) of PTB7:PC71BM with CuPc thickness of (a) 0 nm, (b) 3 nm, (c) 7 nm, (d) 9 nm, (e) 15 nm. AFM 3D image (5 µm× 5 µm) of PTB7:PC71BM with different thickness of CuPc capping layer, (f) 0 nm, (g) 3 nm, (h) 7 nm, (i) 9 nm, (j) 15 nm. The schematic diagram of formation process of thermal evaporation CuPc layer is shown in (k) 0 nm, (l) 3 nm, (m) 7 nm, and (n) 15 nm. 6


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Atomic force microscopy (AFM) images of hybrid active layer with different thickness of CuPc are shown in Figure 2. The preparation condition of hybrid films for AFM measurement is as same as that of PSCs fabrications in order to enable accurate comparison. It can be seen that a little of CuPc deposits filled in the small local concave of the PTB7:PC71BM film surface at the beginning of thermal evaporation. When the thickness of CuPc layer is about 7 nm, some of newly evaporated CuPc molecules are starting to gather together so that a buildup occurs on the top of original thin-CuPc-film, leading to a star distribution of CuPc aggregation. Furthermore, the number of star gradually inclines to aggrandize with the increase of the thickness. However, after the film thickness of CuPc increases to 15 nm, CuPc-aggregation dispersions is becoming to connect together, and the thick film growth mechanism will appear in the upcoming thermal evaporation steps. As shown in the AFM 3D images (Figure 2f to j), it can be found an obvious difference on the surface morphology of PTB7:PC71BM film and CuPc-capping PTB7:PC71BM layer and the surface roughness slightly increased from 1.21 nm (Figure 2a) to 1.68 nm (Figure 2b)，1.73 nm (Figure 2c)，1.79 nm (Figure 2d)，and 1.46 nm (Figure 2e) after the CuPc layer grew onto active layer films. The PTB7:PC71BM film displays relatively unshaped lattice grain morphology and becomes more and more homogeneous with increase of the deposition. Remarkably, the composite PTB7:PC71BM/CuPc film exhibits uniform aligned grains on the surface compared to pristine active layer. The sizes of these aggregates are very small, which is assigned to small aggregated CuPc crystallites, and the layer is therefore rugged. The increased roughness of interlayer, better nanoscale crystallinity, and smaller particles might help improve the physical contact between the buffer layer and the active layer, leading to the decreased series resistance (Rs) and the improved FF.51,52 However, further increase in the thickness of CuPc layer allows the morphology difference to become not very pronounced with original active layer. This rough layer increases the interface defects, which could cause charge carrier interfacial recombination, resulting in a decreased device performance.53 To deeply understand the distinct enhancement of the IPCE spectrum, the UV–Vis absorption of the PTB7:PC71BM films with different thickness of CuPc contents was measured and presented in Figure 3a. Like the trend we observed in the UV–Vis absorption spectra, the device with 3 nm CuPc modification layer shows a holistic absorption enhancement in the region of 330-450 nm and 500-700 nm (two peaks at 475 nm and 610 nm). Especially, while the thickness of CuPc is up to 7 nm, the UV–Vis absorption of the devices gradually enhances over the whole wavelength region of 300-700 7



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nm with the typical absorption peaks of 460 nm, 625 nm, and 680 nm. The visible light harvesting of the devices has been getting higher with the increase of film thickness. Part of this change of the absorption spectra in the whole region is consistent with IPCE spectrum, which reveals the increase of IPCE could result from additional absorption enhancement, heralding efficient harvesting of the photons by optimized device. To investigate the reason of improved optical absorption, Figure 3b exhibits the calculated optical absorption of PTB7: PC71BM/C60 film (watchet imaginary line) and the experimental absorption of PTB7: PC71BM, bare CuPc, and PTB7: PC71BM /CuPc films. The light harvesting indicates a high degree of ordered enhancement from 300 to 750 nm compared to theoretical data, which corresponds to distinct enhancement from light absorption of the CuPc film itself and PTB7: PC71BM film. Optical electric field distribution regulation of device induced by incorporated CuPc film is considered to be the best way to understand the enhanced optical absorption of PTB7: PC71BM film. Electric field intensity distribution of different PTB7:PC71BM/CuPc hybrid device is shown in Figure 3c and the optical electric field distributions of the various thicknesses CuPc based PSCs are presented in Figure 2d-f. The optical electric field of different films shows that the distribution of normalized modulus square of the optical electric field (|E(x)|2) is moving to central zone of the active layer with increased CuPc thickness, which is verified by electric field intensity-distance curve of different PTB7:PC71BM/CuPc composite device in Figure 3c. Furthermore, the absorption edges of the modified devices exhibit the red shift with the increased CuPc thickness, which corresponds to distinct enhancement of the UV–Vis absorption in near infrared region. With the improved optical intensity in the active layer, the absorption of PSCs is supposed to increase, leading to a Jsc improvement, and hence, an improvement of PCE can be expected.54,55 For another, as shown in Figure 2, uniform aligned CuPc improves the physical contact between the buffer layer and the active layer, which reduces inherent interface-trap of optical transmission in the active layer interface, which reduces light scattering and reflection, thus the optical absorption of device is increased.56

8


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Figure 3 (a) Light absorption spectrum of PTB7:PC71BM films with different thickness of CuPc; (b) the comparison of calculated (blue solid line) and experimental (black dotted line) light absorption spectrum; (c), the curves of electric field intensity distribution vs. distance of different PTB7:PC71BM/CuPc composite devices; the optical electric field distribution of the PSCs with different thickness of CuPc films (d) 0 nm, (e) 3 nm, (f) 7 nm, (g) 9 nm.

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Figure 4 (a) Photoluminescence spectra of CuPc and absorption spectra of PTB7 film and PC71BM; (b) photo-produced exciton operating mechanism of CuPc interface; (c) energy transfer diagram of PTB7 and CuPc; (d) the possible pathways of charge transfer between CuPc, PC71BM and PTB7; (e) energy levels alignment of all materials. Figure 4a exhibits photoluminescence excitation spectrum (purple solid line) of CuPc film, light absorption spectra of PTB7 and PC71BM films. The photoluminescence excitation spectrum was excited at 325 nm. As shown in Figure 4a, the PTB7 shows a high absorption in the region of 500 - 750 nm, and PC71BM indicates the broad spectrum from 300 to 600 nm. The total absorption of PTB7 and PC71BM overlaps the wavelength of 300-750 nm (the most effective part in the visible spectrum), which ensures that the strong light trapping could occur in PSCs. Meanwhile, the photoluminescence of CuPc shows a high excitation in the wavelength of 300-750 nm, especially in the wavelength of 400 10


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nm and 700 nm. It can be found that the absorption of PC71BM covered the part of CuPc emission spectra, which ensures them be a energy transfer pair. As shown in Figure 4b, when photon energy strikes the CuPc material, photo-induced excitons flow to the interface of CuPc and PCBM then split, leading to the Jsc increase. Moreover, the absorption of PTB7 also covered the part of CuPc photoluminescence spectra, which enables them to be a good fluorescence resonance energy-transfer (FRET) system.57 To investigate efficient energy transfer between CuPc and PTB7, we calculated the Forster radius

 κ 2QD  FD (λ )ε A (λ )λ4 dλ  4 ∫  n 

(R0) using the equation of R 0 = 9.78 × 10 ×  2

1/ 6

, where

κ

is the

orientation factor of two materials dipoles. QD is the CuPc photoluminescence quantum efficiency. n represents the refractive index. FD is the PTB7 emission spectrum.

εA

is the molar extinction

coefficient of the PTB7. The CuPc and PTB7 molecules have a random orientation, thus

κ 2 =2/3. The

Ro of 8.7 nm was calculated (an effective n of 1.7 and a QD of 0.8 % for CuPc.).58 As shown in Figure 4c, when photon energy strikes the CuPc material, the electron will obtain energy and immediately jump from low energy level orbit to high level orbit of CuPc. The length of R0 between CuPc and PTB7 is less than 10 nm, which suggests that a non-radiative energy transfer process will almost occur between PTB7 and CuPc at the interface of two materials. An energy diagram outlining for the possible pathways of excitated charge from CuPc and PTB7 is shown in Fig. 4d. Additionally, the energy levels alignment of all materials used in our PSCs is listed in Figure 4e. The LUMO and HOMO levels of CuPc are -3.5 eV and -5.2 eV, whose of PC71BM are –3.8 eV and –6.0 eV, respectively, Hence, the photo-generated electron transfer between CuPc and PC71BM happened (pathway 1 in Figure 4d), accompanied by the possible FRET between the CuPc and PTB7 (pathway 2 in Figure 4d).59

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Figure 5 (a) Photoluminescence excitation spectra of PTB7 and CuPc:PTB7, (b) CuPc and CuPc:PC71BM, (c) PTB7:PC71BM/CuPc film with various thickness of CuPc, (d) Photoluminescence time-resolved decay traces of PTB7:PC71BM/CuPc film with different thickness of CuPc. To further explore the hypothesis of a non-radiative energy transfer process certainly occurring, the photoluminescence spectra of PTB7 and PTB7/CuPc was examined and shown in Figure 5a, and both of them were excited at 325 nm. It can be seen that there is significant excitation of PTB7 film, resulting from the maximized excitons recombination within itself. After the CuPc were coated on the PTB7 film, the emission from the composite films decreased because the direct electrons recombination did not occur. Hence, the photo-excited electron transfer from PTB7 to CuPc through the symmetrical interpenetrating interface could happen. Meanwhile, the photoluminescence spectra of CuPc and CuPC/PC71BM films are presented in Figure 5b, the energy transfer from CuPc to PC71BM through the symmetrical interpenetrating interface can also be proved. Figure 5c displays the photoluminescence spectra of PTB7: PC71BM active layer with different thickness of CuPc. When the CuPc thickness was increased, the emission of hybrid films significantly decreases. However, the emission intensity continuously rises when the CuPc thickness is more than 15 nm due to the inside 12


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recombination of interface, which agrees with the results above. The existence of CuPc interfacial layer may strongly impact charge carrier transfer of the device (PTB7 to CuPc, PTB7 to PC71BM, CuPc to PC71BM), and an enhanced charge pumping could facilitate excitons to dissociate. Additionally, the exciton lifetime is inversely proportional to the separation rate, thus the lifetime would decrease with accelerated charge pumping. Figure 5d shows the photoluminescence time-resolved decay traces of PTB7:PC71BM hybrid film without and with different thickness of CuPc, and both of them were tested by Transient State Fluorescence Spectrometer FLS980 and the excited wavelength was 325 nm. It is worth noting that the lifetime reduces from 7.1 ns (0 nm) to 5.8 ns (9 nm), which verified that the exciton dissociation probability has been increased due to the enhanced charge pumping in the interface of device. Furthermore, the optimization of surface topography improved interfacial contact between two materials, resulting in the reduced interface carrier recombination. Hence, the shorter lifetime would be beneficial to weaken the excitons quenching, leading to an improved charge transfer.60,61

Figure 6 (a) J–V characteristics and (b) the impedance spectra of the control and modified devices in dark. To prove the effect of improved surface morphology on the holes transport, the J-V characteristics of devices in dark are shown in Figure 6a. The dark current at reverse bias and leakage current at zero bias are obviously reduced, which increases the diode rectifying ratio of device. Higher current in the space charge limited current dominated regime was achieved, indicating a decrease of series or contact resistance, hence charge carrier transport can be moderately improved. In fact, the uniformly dispersed island-shape CuPc modified layer provide a special hole transport way that hole tend to pass the razor-thin interlayer through the interval of island-shape CuPc in the way of the tunnel effect. Especially, a handful of CuPc deposits filled in the small local concave of the PTB7:PC71BM surface, 13



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which reduced pitfalls and traps for holes transfer, so the improved surface morphology boosted holes transport. Simultaneously, the impedance spectroscopy was measured with an alternating current signal under open circuit voltage in the frequency range of 20 Hz to 2 MHz. The Cole-Cole curve of the impedance spectra for the devices is demonstrated in Figure 6b. The shapes of impedance spectra are all semicircles, which are agree with the parallel R-C combination model. The omega in impedance

image corresponds to the forms of

Z = Rs +

1 1 + jωCrec Rrec

. The series resistance Rs is the

intersection of the semicircle with the Z′ axis. The recombination resistance Rrec is corresponding to the diameter of the semicircle. The capacitance Crec is attributed to the depletion region chemical capacitance due to the connecting to carrier storage. The Rs of photovoltaic cells were calculated according to the intercept of the semicircles with the Z′ axis, which is well identical to the values in Table 1(calculated from J-V curves). Hence, the optimal device reveals the smallest series resistance, which is consistent with the improved charge transfer in modified PSCs. Meanwhile, the smallest series resistance can efficiently enhance FF, leading to a improved PCE. In addition, the decreased diameter of the semicircle means the decreased recombination resistance, which is beneficial to interfacial charge transport.

4.

CONCLUSIONS We have successfully reconstructed anode buffer layer of BHJ solar cells by orienting

microstructures evolution to improve device efficiency. Compared with the control device, the reformative solar cell with 9 nm CuPc interlayer exhibited the highest PCE of 9.726%, resulting from the enhanced FF and Jsc. In this multifunctional system, the uniformly dispersed island-shape CuPc spot accumulations act as not only an optical field spacer but also a multiple energy donor, leading to enhanced spectral absorption and efficient harvesting photo-generated exciton of PSCs. In addition to enhanced light absorption and conversion, the tailored anode energy levels cascading and optimized boundary morphology facilitated efficient charge dissociation and transport and suppressed interfacial bimolecular recombination. This work opens up a new way for the anode interfacial modification of inverted-type polymer solar cells.

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ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. The synthesis of TiO2. The fabrication process and the characteristics of PSCs devices. The AFM image of PTB7:PC71BM layer without CuPc. The AFM top surface of PTB7:PC71BM layer with island-shape CuPc spot accumulations. The summary of the series resistance of all the devices calculating from the impedance sperctrm. AUTHOR INFORMATION Corresponding Author *E-mail: W. B. Guo, [email protected]; L. Zhang, [email protected]. Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS The authors are grateful to National Natural Science Foundation of China (61370046, 11574110), the Science and Technology Innovation Leading Talent and Team Project of Jilin Province (20170519010JH).

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