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A Facile Approach to Prepare a Vanadium Oxide Hydrate Layer as a Hole Transport Layer for High-Performance Polymer Solar Cell Hailin Cong, Dongwei Han, Bingbing Sun, Dongying Zhou, Chen Wang, Ping Liu, and Lai Feng ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 04 May 2017 Downloaded from http://pubs.acs.org on May 5, 2017

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ACS Applied Materials & Interfaces

A Facile Approach to Prepare a Vanadium Oxide Hydrate Layer as a Hole Transport Layer for High-Performance Polymer Solar Cell Hailin Cong,a,b,‡ Dongwei Han,a,b,‡ Bingbing Sun,b Dongying Zhou,b Chen Wang,b Ping Liu,b Lai Fengb,* a

Laboratory for New Fiber Materials and Modern Textile, Growing Base for State

Key Laboratory, College of Chemical Engineering, Qingdao University, Qingdao, 266071, China b

Key Laboratory of Advanced Carbon Materials and Wearable Energy Technologies

of Jiangsu Province, Soochow Institute for Energy and Materials Innovations, College of Physics, Optoelectronics and Energy, Soochow University, Suzhou 215006, China ‡

These authors contribute equally to this work.

*Corresponding

author

(Tel:

+86

512

65223650;

E-mail

address:

[email protected] (Lai Feng)).

1

ACS Paragon Plus Environment


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ABSTRACT We demonstrate a facile and green approach to prepare a vanadium oxide hydrate (VOx·nH2O) layer to serve as the hole transport layer (HTL) in high-performance polymer solar cells (PSCs). The VOx·nH2O layer was in-situ prepared by a combined H2O2 and UVO processing on a VOx layer. The as-prepared VOx·nH2O layer featured a work function of 5.0±0.1 eV, high transmittance and better interface properties compared to the generally prepared VOx (UVO or thermal annealing) layers. PSCs based on PTB7-th:PC71BM using the VOx·nH2O layer as HTL yielded high power conversion efficiencies (PCEs) up to 8.11%, outperforming the devices with the VOx layers (PCE of 6.79% for UVO processed VOx layer and 6.10% for thermal annealed VOx layer) and conventional PEDOT-PSS layer (PCE of 7.67%). The improved PCE was attributed to the enhanced JSC and/or FF, which mainly correlates to the improved interfacial contact between the photoactive layer and ITO/HTL or cathode when using the VOx·nH2O layer as HTL. Similar improvement in PCE was also observed for the PSCs based on P3HT:PC61BM. In addition, PSCs with a VOx·nH2O layer as HTL showed higher stability than those with a PEDOT:PSS layer. Hence, it would be possible to use this simply and in-situ prepared VOx·nH2O layer as an inexpensive HTL for high-performance PSCs.

KEYWORDS: polymer solar cells, hole transport layer, vanadium oxide hydrate, H2O2-UVO processing, interfacial contact

2


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1. INTRODUCTION Polymer solar cells (PSCs) have received recent attentions owing to their advantages

of

lightweight,

flexibility,

low-cost

and

environment-friendly

characteristics.1-4 Through long-term efforts, the efficiency of single-junction PSCs has been steadily increased up to >10%,5-8 which makes them competitive alternatives or supplementary to the silicon or inorganics-based photovoltaics. Nevertheless, in order to realize the practical use of PSCs in near future, their stability issue and applicability for large-scale production (for example, a roll-to-roll process) still need to be significantly improved.9-12 The interface layers (i.e., hole transport layer and electron transport layer) between the electrode and the photoactive layer are important components of PSC, which are of remarkable benefit to the charge separation and charge collection.13,14 Particularly, polyethylenedioxythiophene:polystyrenesulfonate (PEDOT:PSS) has been

widely

used

for

preparing

hole

transport

layer

(HTL).

However,

PEDOT:PSS-based HTL is still far from being ideal choice due to its high-cost as well as unfavored acidic and hygroscopic natures,15 which not only increase the fabrication cost but also lead to reduced stability of PSCs. Alternatively, a variety of semiconducting transition metal oxides such as NiOx,16-18 MoOx,19-22 VOx,23-27 CuOx28,29 and WO3,30,31 ReOx,32 have been developed as HTL materials for fabricating high-stability and cost-effective PSCs. Among them, VOx is particularly promising because of its low-cost, high ambient stability, nice optical and electrical properties. In early works, V2O5-based HTL was prepared via vacuum thermal evaporation.33-35 3



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However, such a technology requires expensive facilities, which shows low compatibility with the easy processing of PSCs. Recent works focus on low-temperature solution-processed V2O5 or VOx. In a typical study, Hou J. H. et al. reported using hydrogen vanadium bronzes (HxV2O5), prepared by the reaction of vanadium metal powder and H2O2 in presence of ethanol,23 to fabricate HTL for achieving high-performance PSCs. Though device tests revealed that the performance of HxV2O5-based PSCs was still inferior to that of the standard device with a PEDOT:PSS layer, the effectiveness of vanadium oxides as HTL was clearly evidenced. In a more advanced study, Yang R. Q. et al. demonstrated another V2O5-based HTL processed by O2 plasma, which even outperformed the conventional PEDOT:PSS layer due to the excellent surface property.25 Nevertheless, such a processing is not suitable for large-scale fabrication of PSCs owing to the fact that the generation of O2 plasma usually requires an expensive equipment. Moreover, in recent studies, vanadium pentaoxide hydrate (V2O5·nH2O) sol made by aging metavanadic acid solution or through a melting-quenching sol−gel method was applied as HTL in PSCs.26,27 Though the V2O5·nH2O-based PSCs exhibited better performance than that of the standard device with a PEDOT:PSS layer, their cost effectiveness is relatively lower due to the long time aging of metavanadic acid (ca. 20 days) or high-temperature melting of V2O5 (ca. 800

o

C). A facile approach for high

cost-effectiveness thus remains to be achieved. According to previous works, vanadia gels can be alternatively prepared by a simple and green reaction of V2O5 and H2O2.36-40 Taking this strategy into account, in 4


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this work, we report a facile way to prepare a vanadium oxide hydrate (VOx·nH2O) based HTL for PSCs, in which a combined H2O2 and UVO processing was introduced after short-time thermal annealing of vanadyl acetylacetonate (VO(acac)2) layer. The in-situ prepared VOx·nH2O layer exhibited improved interfacial properties as compared to the UVO-only processed or thermally annealed VOx layer. Hence, when the

VOx·nH2O

layer

was

used

as

HTL

in

the

PSCs

based

on

poly[(ethylhexyl-thiophenyl)-benzodithiophene-(ethylhexyl)-thienothiophene]:[6,6]phenyl-C71-butyric

acid

methyl

ester

(PTB7-th:PC71BM)

or

poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM), improved PCE with enhanced FF and Jsc was observed. In addition, when comparing with the standard devices, in which PEDOT:PSS layer was used as HTL, the devices with VOx·nH2O layer showed comparable or even improved PCEs with higher stability. 2. EXPERIMENTAL 2.1 Chemicals Vanadyl acetylacetonate (VO(acac)2) (97%) was purchased from Alfa-Aesar. H2O2 (30%) and isopropyl alcohol were purchased from Sinopharm Jiangsu Co. Ltd. PTB7-th, P3HT and fullerene acceptors (PC61BM and PC71BM) were provided by Nano-C Inc.. PEDOT:PSS (Al 4083, Clevios) was purchased from H. C. Stark company. 2.2 VOx·nH2O thin film preparation 5 mg VO(acac)2 was dissolved into 5 mL isopropyl alcohol and the solution was 5



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ultra-sonicated for 3-4 h. After that, the VOx·nH2O layer was prepared as follows. Firstly, the VO(acac)2 solution was filtered with a filter (0.45 µm) and spin-casted on an ITO substrate at 2000 rpm for 30 s, followed by a short-time thermal annealing (150 oC for 2-3 minutes in air). Then, 30% H2O2 (30-40 µL) was spin-casted on the as-prepared VOx layer at 2000 rpm for 30 s and the layer was subjected to an ultraviolet-ozone (UVO) treatment (Ultraviolet Ozone Generator, T1OX10/OES, UVOCS Inc., USA) for 10 min. The as-prepared layer is denoted as VOx·nH2O (H2O2-UVO) layer. In control experiments, a VOx (UVO-only) layer or a VOx (annealing-only) layer was prepared by spin-casting VO(acac)2 solution on an ITO substrate, followed by a UVO treatment (for 10 min) or a thermal annealing process (150 oC in air for 15 min). 2.3 Thin film characterizations X-ray photoelectron spectra (XPS) were recorded with an ESCALAB 250 spectrometer with a Al Kα excitation source. The work function of the VOx·nH2O layer was estimated by ultraviolet photoelectron spectroscopy (UPS) on an AXIS Ultra-DLD using HeI irradiation with hv=21.22 eV. Fourier transform infrared (FTIR) spectra were recorded with a Nicolet 510 spectrometer. Raman spectra were obtained on an instrument (Renishaw inVia-reflex) using a 532 nm excitation laser. Transmittance spectra were obtained on a Shimazu UV2600 spectrometer. Atomic force microscopy (AFM) measurements were conducted on a MFP-3D-BIO (Asylum Research) system in tapping mode. Raman spectra was obtained on an instrument (Horiba Jobin Yvon) using a 532 nm laser as excitation source. The contact angle was 6


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measured on a system of MY-SPCX1-01 (Yuming Tech., China). 2.4 Device fabrication and characterizations The PSCs were fabricated with a standard configuration (ITO/HTL/active layer/cathode). The ITO glass was cleaned following a previously reported method.41 Next, VOx·nH2O and various VOx layers were prepared on the ITO substrate as mentioned above. Alternatively, PEDOT:PSS layer with a thickness of 40-60 nm was prepared.41 Then, a photoactive layer was prepared following a previously reported method.41 Finally, the cathode (Ca/Al: 20/80 nm) was vacuum deposited (ca. 10-5 Pa) on the photoactive layer with a shadow mask, giving an active area of 4 mm2. The current density–voltage (J–V) characteristics were measured under a standard condition (AM. 1.5 G) with a Keithley 2400 SourceMeter. The incident photon-to-current conversion efficiency (IPCE) spectra were recorded on a QE-R3011 system (Enli Tech., China). The

hole-only

device

with

a

configuration

of

ITO/HTL/

PTB7-th:PC71BM/MoO3/Ag was fabricated for space-charge-limited-current (SCLC) measurement. The fabrication details were provided in Supporting Information (SI). The hole mobility was calculated from the J-V curve obtained in dark (see SI). 3. RESULTS AND DISCUSSION 3.1. Characterizations of the VOx·nH2O layer. XPS studies were carried out to investigate the chemical compositions of the in-situ prepared VOx·nH2O (H2O2-UVO) layer. Fig. 1 presents the O 1s and V 2p high-resolution spectra of the VOx·nH2O (H2O2-UVO) layer, in comparison with 7



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those of UVO-only processed VOx layer. Particularly, the O1s spectrum of the VOx (UVO-only) layer can be fitted into two peaks at 530.4 and 531.6 eV, corresponding to the oxygen species in metal oxide (VOx) and undecomposed precursor (C=O), respectively.42-45 This indicates that most vanadium precursors have been converted to vanadium oxides through a UVO process, similar to those obtained from a thermal annealing process.20 As for the VOx·nH2O (H2O2-UVO) layer, a broader O 1s spectrum was observed, in which additional fitting peak at 533.1 eV can be identified, pointing to the O species in H2O or OH group.46,47 This result indicates that coordinated H2O molecules or OH groups have been introduced during the H2O2-UVO processing due to the reaction between H2O2 and thermally generated VOx.23 On the other hand, similar V 2p spectra were obtained for the VOx·nH2O (H2O2-UVO) and VOx (UVO-only) layers: Either V 2p3/2 or V 2p1/2 profile can be deconvoluted into two peaks (517.7 and 516.8 eV for V 2p3/2; 525.0 and 523.6 eV for V 2p1/2), corresponding to V5+ and V4+ oxidation states, respectively.21,41,42 The presence of V4+ might be resulted from the partial reduction of V5+ due to the UVO or H2O2-UVO treatment. Particularly, in the VOx·nH2O (H2O2-UVO) layer, the ratio of V5+ to V4+ is 2.3:1, while the VOx (UVO-only) layer gives a ratio of 3:1. The slightly higher V4+ content in the VOx·nH2O (H2O2-UVO) layer might indicate more oxygen vacancies formed during the H2O2-UVO process and hence better electric conductivity of the layer.

8


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Fig. 1 (a) XPS spectra of V 2p and O 1s of (a) the VOx·nH2O (H2O2-UVO) layer, in comparison with (b) the UVO-only processed VOx layer.

Fig. 2 FT-IR spectra of the VOx·nH2O (H2O2-UVO) and VOx (UVO-only) layers.

Fig. 2 presents the FTIR spectrum of the as-prepared VOx·nH2O (H2O2-UVO), in comparison with the UVO-only processed VOx. In both spectra, it is clearly seen the characteristic peaks of the stretching vibration of V=O (997 cm-1) and H–O (around 3500 cm-1). Nevertheless, in the spectrum of VOx·nH2O (H2O2-UVO), the 9



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characteristic peak of H-O is much more intensive than that observed for the UVO-only processed VOx, indicating additional OH groups or water molecules were introduced via the H2O2 processing. Moreover, the micro-Raman spectra of the as-prepared VOx·nH2O (H2O2-UVO) and VOx (UVO-only) layers are shown in Fig. S2. Both spectra showed bands at 989, 685, 519, 477, 423, 280 and 138 cm-1, corresponding to V2O5.40,48 Besides, additional bands at 872 and 158 cm-1 were observed for the VOx·nH2O (H2O2-UVO) layer, indicating the presence of coordinated H2O molecules or OH groups. Thus, this is fully consistent with the XPS result, confirming the formation of vanadium oxide hydrate (VOx·nH2O) through the H2O2-UVO processing. UPS was employed to estimate the work function (WF) of the as-prepared VOx·nH2O (H2O2-UVO) layer. Fig. 3 provides the secondary electron cutoff spectra. The WF of the VOx·nH2O (H2O2-UVO) layer spin-coated on an ITO substrate is calculated to be 5.0±0.1 eV, slightly lower than that of the PEDOT:PSS layer (5.1±0.1 eV) measured under the same conditions or reported in the literatures.49 In addition, the as-prepared VOx·nH2O (H2O2-UVO) layer is highly transparent in the range of 500-800 nm (see transmittance spectra in Fig. S3), similar to that of the VOx (UVO-only) layer as well as the PEDOT:PSS layer. Such an optical feature allows the use of this VOx·nH2O (H2O2-UVO) layer as HTL for PSCs.

10


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Fig. 3 UPS spectra of PEDOT:PSS and VOx·nH2O (H2O2-UVO) layers.

The surface morphologies of the VOx·nH2O (H2O2-UVO) and VOx (UVO-only) layer were characterized by tapping-mode atomic force microscopy (AFM). As shown in Fig. 4a-c, the VOx·nH2O (H2O2-UVO) layer demonstrates a uniform surface with a root-mean-square (rms) roughness of 2.53 nm. It is lower than that of the VOx (UVO-only) layer (5.13 nm) though higher than that of the PEDOT:PSS layer (1.22 nm), suggesting that additional H2O2 treatment yielded the in-situ formation of VOx·nH2O layer with reduced surface roughness. In addition, the topography of PTB7-th:PC71BM photoactive layers on top of different HTL layers are present in Fig. 4d-f. The rms roughness of the blend film deposited on the VOx·nH2O (H2O2-UVO) layer is 0.56 nm, remarkably lower than that of the blend film on VOx (UVO-only) layer (1.14 nm) and PEDOT:PSS layer (1.07 nm). These results suggest that a smoother photoactive film can be obtained on the top of VOx·nH2O (H2O2-UVO) layer. Hence, the interfacial contact between the active layer and the top electrode can be improved, which benefits charge collection. 11



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Fig. 4 AFM images of HTL layers: (a) VOx·nH2O (H2O2-UVO) layer, (b) VOx (UVO-only) layer, (c) PEDOT:PSS layer, (The AFM image of a bare ITO is present in Fig. S4 as reference.) and (d,e,f) AFM topography images of active layers (AL: PTB7-th:PC71BM) on top of different HTL layers. The scan size is 10 µm × 10 µm. To better understand the influence of H2O2-UVO treatment to the VOx·nH2O interface, we carried out contact angle measurements and the results are shown in Fig. 5. Particularly, the water contact angle of the VOx·nH2O (H2O2-UVO) layer is 11.1°, lower than those observed for the VOx (UVO-only) layer (14.4°) and the VOx (annealing-only) layer (61.2°) as well as the PEDOT:PSS layer (19.7o or 22.17o).25 The low water contact angle of the VOx·nH2O (H2O2-UVO) layer might indicate the presence of many dangling bonds on the surface of the layer, which lead to substantial surface reconstruction and benefit interfacial contact.25 Moreover, as seen in Fig. S5, the contact angle of 1,2-dichlorobenzene on the VOx·nH2O (H2O2-UVO) layer (7.8°) 12


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is also slightly lower than those for the VOx (UVO-only) layer (10.4°) and the PEDOT:PSS layer (10.8o), suggesting a slightly better wettability for the VOx·nH2O (H2O2-UVO) layer. Thus, the combined feature of smooth surface and good wettability can account for the formation of a more uniform active layer on the VOx·nH2O (H2O2-UVO) layer as discussed above.

Fig. 5 Measured water contact angle for different HTL. VOx·nH2O (H2O2-UVO), VOx (UVO-only), PEDOT:PSS and VOx (annealing-only) layers from top to bottom, respectively.

3.2 Photovoltaic Performance of the device with a VOx·nH2O layer. To investigate the performance of the VOx·nH2O (H2O2-UVO) layer as HTL, it was applied to fabricate the PTB7-th:PC71BM based PSC with a configuration of ITO/HTL/active layer/Ca/Al. For comparison, a series of PSCs with a PEDOT:PSS 13



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layer or differently processed VOx layer were prepared, optimized and tested. Fig. 6a illustrates the J−V curves of various PSCs under optimized conditions (see Table S1 and Fig. S6 in SI). The averaged device performance and the best PCE values are listed in Table 1. Obviously, the best photovoltaic performance was obtained from the device B with a VOx·nH2O (H2O2-UVO) layer. The average PCE reaches to 7.97% with an open-circuit voltage (VOC) of 0.78 V, a fill factor (FF) of 64.62% and a short-circuit current density (JSC) of 15.76 mA/cm2. However, only moderate PCEs were achieved in the devices C (6.58%) and D (6.04%) with differently processed VOx layers (i.e., UVO or annealing-only) due to their lower VOC, FF and JSC. Additionally, it is found that device B is even superior to the standard device A with a PEDOT:PSS layer, which gave a lower average PCE of 7.52% with a VOC of 0.790 V, a JSC of 14.39 mA/cm2, and an FF of 66.22%, all comparable to those reported in recent literatures.50,51 These results suggest that the VOx·nH2O layer prepared through a simple H2O2-UVO processing might possess a better hole-transport or hole-collection property compared to the regularly prepared VOx layers as well as the conventional PEDOT:PSS layer. Furthermore, to ascertain the accuracy of the J-V results, IPCE spectra were measured for the devices A, B and C. As shown in Fig. 6b, similar IPCE spectra were observed for these devices. Particularly, device B exhibited slightly higher IPCE value in the range of 400-750 nm relative to those of the devices A and C, indicating a better charge collection efficiency of the VOx·nH2O (H2O2-UVO) layer in this range. The calculated Jsc is 14.68 mA/cm2 for device A, 15.80 mA/cm2 for device B and 14.60 14


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mA/cm2 for device C, all of which are close to those obtained from the J-V tests, respectively, with an error within 5%. To better understand the slightly higher Jsc of device B relative to those of devices A and C, their J-V characteristics were measured in dark. As shown in Fig. 6c, the current density at reversed biases from device B is smaller than those of devices A and C, indicating a reduced leakage current in device B.52,53 This result is in good agreement with its larger shunt resistance Rsh (938 Ω cm2) relative to device A (532 Ω cm2) and smaller series resistance Rs (6.2 Ω cm2) relative to device C (7.7 Ω cm2, see Table 1). Thus, the higher Jsc of device B might be understood by the enhanced Rsh or reduced Rs,54 which mainly correlates to the better interfacial contact between ITO/HTL and active layer when using a VOx·nH2O (H2O2-UVO) layer as the HTL.

Fig. 6 (a) J−V curves of the best performing devices with different HTLs under 1000 W/m2 AM 15



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1.5G illumination. (b) IPCE curves along with integrated current densities. (c) J−V curves in dark. The device structure is ITO/HTL/PTB7-th:PC71BM/Ca/Al. Table 1. Device performance of the PSCs based on PTB7-th:PC71BM with different HTLs.a

device

A

VOC

JSC

FF

(V)

(mA/cm2)

(%)

0.790

14.39

66.22

0.784

15.76

hole transport layer

PEDOT:PSS

Rs(Ω

Rsh(Ω

cm2)c

cm2)d

7.52(7.67)

6.0

532

64.62

7.97(8.11)

6.2

938

PCE (%)b

VOx·nH2O B (H2O2-UVO) C

VOx (UVO-only)

0.762

14.60

59.20

6.58(6.79)

7.7

901

D

VOx (annealing-only)

0.768

14.14

55.70

6.04(6.10)

11.8

507

a

Statistical data achieved from 10 independent devices. bThe maxima PCEs are in the brackets. c,d

Rs and Rsh were defined using the method reported in literatures.55-57

To explore the hole transport characteristics of the VOx·nH2O (H2O2-UVO) layer, the SCLC measurements were performed and the Mott−Gurney equation58-60 was employed for calculating the hole mobility (µh): JSCLC=9ε0ετµh(V-VBI)2/(8L3). The definitions for ε0, ετ, V, VBI, L and the calculation details for µh are described in SI. The dark J-V curves of hole-only devices are present in Fig. 7. The µh of the device with the

(H2O2-UVO) layer was determined to be 5.59×10-4 cm2 V-1 s-1, higher than that

of the devices with the VOx (UVO-only) layer (3.66×10-4 cm2 V-1 s-1). These results indicate that the hole injected from the active layer, could be more easily extracted for the device with a VOx·nH2O (H2O2-UVO) layer, in agreement with the improved FF as suggested by the J-V tests. The enhanced µh of the hole-only device with a VOx·nH2O (H2O2-UVO) layer further illustrates the positive effect of the improved interface properties for hole extraction. 16


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Fig. 7 J-V characteristics of the hole-only devices with different HTLs. The fitting results are given as solid lines.

To check the viability of the VOx·nH2O (H2O2-UVO)-based HTL, the PSCs based on P3HT:PC61BM was fabricated. As P3HT is a representative wide bandgap polymer donor, it is very different from the above used low bandgap polymer of PTB7-th. Nevertheless, similar results were obtained (see Table S2 and Fig. S7): the device B′ with a VOx·nH2O (H2O2-UVO) layer demonstrated a superior photovoltaic performance to those of the devices C′, D′ with differently processed VOx layers (UVO or annealed layer). The PCE of device B′ is even comparable to that of the standard device A′ with a PEDOT:PSS layer. The long-term stabilities of devices with PEDOT:PSS and VOx·nH2O (H2O2-UVO) layers, respectively, stored under N2 atmosphere are exhibited in Fig. 8. The device with a VOx·nH2O (H2O2-UVO) layer maintained nearly 85% of its initial PCE after 20 days. Meanwhile, the device with a PEDOT:PSS layer experienced a faster decay with the PCE decreasing to ca. 60% probably owing to the presence of a corrosive and hygroscopic PEDOT:PSS layer. These results suggest that the VOx·nH2O-based HTL features higher stability as compared to the PEDOT:PSS layer, 17



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which makes it more viable HTL for PSCs.

Fig. 8 Degradation of encapsulated devices at room temperature under an N2 atmosphere.

4. CONCLUSIONS In summary, we demonstrated a facile in-situ preparation of VOx·nH2O layer through a combined H2O2-UVO processing on VOx layer, which can be used as HTL for high-performance PSCs. The composition of the as-prepared VOx·nH2O (H2O2-UVO) layer was confirmed by using the XPS, FT-IR and Raman spectroscopies. Further characterizations revealed that the VOx·nH2O (H2O2-UVO) layer features a proper work function of ca. 5.0±0.1 eV, a high transmittance, a good wettability and a smooth surface with many dangling bonds. All these features may induce energy alignment for ITO/HTL/active layer and facilitate the formation of a uniform photoactive layer as well as good interfacial contacts in PSCs. As a result, the PSCs based on PTB7-th:PC71BM with a VOx·nH2O (H2O2-UVO) layer yielded an average PCE of 7.97% with high stability. The PCE is improved by ~32% compared 18


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to the devices with the VOx layers and superior to the device with a conventional PEDOT:PSS layer. In addition, the VOx·nH2O (H2O2-UVO) layer was also applicable for P3HT:PC61BM based PSC, giving an average PCE of 3.24%. Thus, the VOx·nH2O (H2O2-UVO) layer reported in this work can be considered as a promising alternative to the conventional PEDOT:PSS layer for high-performance and cost-effective PSCs. ASSOCIATED CONTENT Supporting Information

Schematic molecule structures; Raman spectra; optical transmittance spectra; AFM image, contact angle images; device parameters and J-V curves of the PSCs based on PTB7-th:PC71BM and P3HT:PC61BM, respectively; details for SCLC measurements. This material is available free of charge via the Internet at http://pubs.acs.org. ACKNOWLEDGEMENTS We cordially thank Prof. Zexin Zhang, Mr. Qiang Tao (Soochow University) for the kind help in the contact angle measurements. The work is supported in part by the NNSF of China (No. 51372158), the NSF of Jiangsu Province (No. BK20160325) and Suzhou key laboratory for advanced carbon materials and wearable energy technologies. In addition, this work is also in part supported by Collaborative Innovation Center (CIC) of Suzhou Nano Science and Technology.

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Facile Approach to Preparing a Vanadium Oxide ... - ACS Publications

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