Accepted Manuscript

Title: CH3NH3PbI3 Perovskite Sensitized Solar Cells Using aD-A Copolymer as Hole Transport Material

Author: P. Nagarjuna K. Narayanaswamy T. Swetha G.Hanumantha Rao Surya Prakash Singh G.D. Sharma

PII: S0013-4686(14)02180-XDOI: http://dx.doi.org/doi:10.1016/j.electacta.2014.11.003Reference: EA 23675

To appear in: Electrochimica Acta

Received date: 12-8-2014Revised date: 30-10-2014Accepted date: 1-11-2014

Please cite this article as: P.Nagarjuna, K.Narayanaswamy, T.Swetha, G.HanumanthaRao, Surya Prakash Singh, G.D.Sharma, CH3NH3PbI3 Perovskite Sensitized SolarCells Using a D-A Copolymer as Hole Transport Material, Electrochimica Actahttp://dx.doi.org/10.1016/j.electacta.2014.11.003This is a PDF file of an unedited manuscript that has been accepted for publication.As a service to our customers we are providing this early version of the manuscript.The manuscript will undergo copyediting, typesetting, and review of the resulting proofbefore it is published in its final form. Please note that during the production processerrors may be discovered which could affect the content, and all legal disclaimers thatapply to the journal pertain.

CH3NH3PbI3 Perovskite Sensitized Solar Cells Using a D-A Copolymer as Hole Transport Material P. Nagarjuna1, K. Narayanaswamy1, T. Swetha1, G. Hanumantha Rao1, Surya Prakash Singh1* and G. D. Sharma2* 1Inorganic and Physical Chemistry Division, CSIR-Indian Institute of Chemical Technology, Uppal road, Tarnaka, Hyderabad-500007, India 2R & D Center for Engineering and Science, JEC group of Colleges, Jaipur Engineering College, Kukas, Jaipur 303101, India Graphical abstract fx1 Abstract A conjugated D-A copolymer (P) having benzodithiophene donor and

benzo[1,2,5]thiadiazole acceptor was employed as a p-type hole transporting material in solid

state organicinorganic hybrid solar cells and compared with the P3HT hole transporting

material. In these device we have used organo-lead halide (CH3NH3PbI3) synthesized by us,

as light harvester. The power conversion efficiency (PCE) of 6.64 % is achieved for the solar

cell with P which is higher than that for P3HT (4.24 %). The increase in PCE is mainly due to

the enhancement in FF and Voc and attributed to higher mobility of hole for conjugated

copolymer than P3HT.

Key words: Inorganic-organic hybrid solar cells, perovskite, donor--acceptor, hole transport

material, power conversion efficiency.

* Corresponding authors

spsingh@iict.res.in (Surya Prakash Singh)

Tel: +91-40-27191710; Fax: +91-40-27160921

gdsharma273@gmail.com (G. D. Sharma)

1. Introduction

Dye sensitized solar cells received considerable attention since the first report on 1991 by

Grtzel and his coworkers, due to the excellent power conversion efficiency (PCE) of about

7% at a relatively low cost of fabrication1 and are alternative to the conventional silicon

based solar cells. A typical DSSC uses a monolayer of light absorbing sensitizer anchored on

nanocrystalline TiO2 to enhance light harvesting in a mesoporous environment in which

ACCE

PTED

MAN

USCR

IPT

charge separation also occurs at this surface. Lot of research has been carried out to enhance

the PCE of these devices. As a result, PCE of 12.3 % has been reported in 2011, by Grtzel

research group for DSSCs based on an ortho-substituted porphyrin sensitizer, YD2-oC8,

cosensitized with organic dye (Y123) with a cobalt electrolyte2 which opened a new research

area on porphyrin sensitized DSSCs.3 However, the absorption spectrum of this porphyrin

dye covers only the visible spectral region and lack of light harvesting ability beyond 700 nm

limits the further enhancement in PCE for the DSSCs based on porphyrin dyes. Moreover, the

long term stability of these devices might be an issue for future commercialization due to the

use of volatile electrolytes. Various inorganic light absorbers with light harvesting capability

that extends into the near infrared region were hence sought to replace these organic dyes.

Recent studies have reported that organometal halide perovskite mesoscopic solar

cells with promising PCEs due to their excellent light harvesting and electron transporting

properties and are perfectly suitable for use as prospective photovoltaic materials. In 2009,

Miyasaka et al. reported the first perovskite (CH3NH3PbBr3) sensitized TiO2 solar cell using

liquid electrolytes based on iodide and bromide and achieved a PCE of 3.1 % under one sun

illumination and 3.8 % when CH3NH3PbBr3 was replaced by CH3NH3PbI3.4 Later on Park et

al.5 in 2011, reported improved PCE of 6.5 % for modified TiO2 solar cells sensitized with

CH3NH3PbI3 perovskite and an electrolyte based on iodide. They have used Pb(NO3) for

modify the surface of mesoporous TiO2 film before coating of perovskite film and acts as

blocking layer in the solar cells. However, it was observed that the performance of devices

based on perovskite materials and liquid electrolyte decreased by 80 % in only few hours due

to the instability of the perovskite material in the presence of liquid electrolyte due to the

dissolution of perovskite. Hence it is essential to prepare perovskite based solar cells with a

solvent free hole transport material (HTM) and called as solid state organic-inorganic hybrid

solar cells. Park and coworkers6 reported sub-micrometer thin film solid state solar cells

attaining a PCE of 9.7 % with a CH3NH3PbI3 in mesoporous TiO2 film. 7 Snaith and co-

workers reported a similar perovskite, CH3NH3PbI3Cl that served as a light absorber for

mesoscopic thin film solid state solar cells to attain a PCE of 10.9%, for which the

mesoporous Al2O3 film served as scaffold to replace the n-type TiO2 electron transporting

layer. Recently, same group reported a significant enhanced PCE of 12.3% 8 for perovskite

CH3NH3PbI3-xClx solar cells, with the same device structure based on Al2O3. Soak et al.

reported almost same PCE for solar cell based on another perovskite CH3NH3Pb(I1-xBrx)3,

with the mesoporous TiO2 photoanode.9 Recently, in 2013, Grtzel and co-workers, reported

perovskite CH3NH3PbI3 sensitized TiO2 solar cells with a PCE approaching to 15 % which

ACCE

PTED

MAN

USCR

IPT

set a new record for all solid state hybrid mesoscopic solar cells.10 Therefore, this impressive

PCE opened new channel for the development of third generation solar cells based on

perovskite and HTM with the advantages of very high PCE, low cost, ease of processing and

considerable durability11 and efficiency approaching 20% is realistically possible from a

solid-state mesoscopic solar cell based on CH3NH3PbX3 (X = Cl, Br, or I).12 In all above

perovskite solar cells, a HTM [2,2,7,7-tetrakis-(N,N-di-pmethoxyphenylamine) 9,9-spiro-

bifluorene] (spiro-OMeTAD) has been employed. However, conductivity of spiro-OMeTAD

is low (~10-5 S/cm). Moreover, the spirobifluorene core in spiro-OMeTAD molecule is

relative expensive due to extensive synthetic processes for preparation. So it would be

important to develop a cheaper alternative of spiro-OMeTAD for commercial application of

hybrid perovskite solar cells.

Alternative HTM materials with excellent electrical properties may be used in place

of spiro-OMeTAD. Soluble donor--acceptor (D--A) can be the alternative choice as HTM.

Conjugated polymers have been widely used in the field of polymer solar cells because of

their easy processability, low cost and mechanical flexibility.13 The solar cells using the

combination of perovskite with mesoporous TiO2 and P3HT as hole transport material, PCEs

of 3.8 %, 4.5 %14 and 6.7 %15 have been reported and recently a PCE of 10.8 % have been

achieved by Coning et al. for CH3NH3PbI2Cl perovskite.16

To obtain high photovoltaic performance, it is importance that the HTM should show

a good hole mobility and compatible highest occupied molecular orbital (HOMO) energy

level to the semiconductor light absorber. Recently, Qiu, have used a p-type low band gap

conjugated D-A copolymer PCBTDPP as HTM and achieve an outstanding open circuit

voltage of about 1.15 V for CH3NH3PbBr3 sensitized hybrid solar cells and CH3NH3PbI3

sensitized hybrid solar cell showed a PCE of 5.55% along with good stability.17 Heo et al

have reported a ~12 %18 PCE in an organic-inorganic hybrid solar cell using a poly

(triarylamine) (PTAA) HTM with an average PCE of 9.7% 19 The D-A conjugated polymer P

(chemical structure shown in Figure 1) have the deeper HOMO level than P3HT and posses

good stability than P3HT. Recently, Sharma et al have used this copolymer as donor material

for polymer solar cell along with PCBM and achieved a PCE of 3.45-5.30%.20 These

demonstrations indicate that the P can be used as HTM for hybrid solar cells.

In the present communication, we have used D-A conjugated copolymer P as HTM to

investigate the solid state hybrid solar cells consisting of CH3NH3PbI3 as the light harvester

and mesoporous TiO2 as photoanode. We have also fabricated the solar cells using P3HT as

ACCE

PTED

MAN

USCR

IPT

HTM for comparison. The inorganic-organic hybrid solar cell with P as hole transport

material (PCE=6.64 %), showed higher PCE than that for P3HT (PCE=4.24 %) and attributed

to the higher hole mobility of P as compared to P3HT. The enhancement in Voc and FF for

cell with P has been related to the deeper HOMO energy level of P and efficient hole

transport, respectively.

2. Experimental details Perovskite was synthesized following the reported procedure.6 The P3HT was purchased

from Aldrich and copolymer was synthesized as reported earlier.20

2.1 Device fabrication and characterization

A 40 nm thick dense blocking layer of TiO2 was deposited onto the pre-cleaned FTO

substrate by spraying pyrolysis deposition carried out using a 20 mM titanium diisopropoxide

bis(acetylacetone) solution (Aldrich) at 450 C to prevent direct contact between FTO and

HTM. The mesoporous TiO2 films were coated from a TiO2 paste (dye Sol 18NT-T paste

diluted in anhydrous ethanol) by doctor blade technique. The films were dried at 80 C for 1

min and then annealed at 450 C for 30 min. The films were then treated in 40 mM of TiCl4

aqueous solution at 60 C for 1 hr and heat treatment at 450 C for 30 min to improve the

interfacial contact with nanocrystalline TiO2. The perovskite CH3NH3PbI3 solution was

prepared as follow. The synthesized CH3NH3I powder was mixed with PbI2 at a 1:1 mol

ratio in dimethylformamide (DMF) and stirred over night at 60 C, followed by filtering

using a Whattman (0.45 m) filter paper. The prepared solution of perovskite was dripped on

the top of TiO2 film and then spin cast at 2500 rpm for one minute. After that the perovskite

sensitized TiO2 film was placed on a top of hot plate at 100 C for 45 min to form crystalline

CH3NH3PbI3. The heat treatment is essential for a complete conversion of precursor to final

organo lead halide. The heated CH3NH3PbI3 film exhibits better optical absorption and higher

crystallinity.21 We have used P3HT (commercially available and used without any further

purification) and copolymer P. The polymer HTMs were spin coated on

CH3NH3PbI3/TiO2/bl-TiO2 /FTO substrate at 2500 rpm for 30s using HTMs solution in

chlorobenzene and then dried for 1 hr. Finally a gold (Au) cathode electrode was deposited

by thermal evaporation using a shadow mask to fix the active area of device around 0.20 cm2.

The current-voltage (J-V) characteristics under illumination as well as in dark, of the

devices were recorded using a Keithley source meter (model 2400). A xenon lamp coupled

with AM 1.5 optical filter (100 mW/cm2) was used as light source for illumination. The

incident photon to current conversion efficiency (IPCE) of the devices was measured using a

ACCE

PTED

MAN

USCR

IPT

monochromator and xenon lamp as light source and resulting photocurrent was measured

with source meter under short circuit condition.

3. Results and discussion The optical UV-visible absorption spectra of perovskite CH3NH3PbI3 thin film is

shown in Fig. 2. It can be seen from this figure that the thin film of synthesized perovskite

(annealed at 100 C) absorbs a wide range of light from visible to the near infrared with an

absorption onset at 790 nm, indicating the formation of CH3NH3PbI3 film on the substrate22.

The CH3NH3PbI3 film exhibits an absorption peak around 370 nm and a shoulder band at 484

nm. The optical band gap estimated from the absorption onset wavelength is 1.57 eV is in

agreement with the value reported in literature. We had also characterized the thin film of

CH3NH3PbI3 by X-ray diffraction and shown in Fig. 3. The appearance of strong peaks at

2=13.98, 28.32 and 31.74 corresponds to the (110), (220) and (310) planes, indicates the

formation of the tetragonal perovskite structure.23

We have used a low bandgap D-A copolymer with 4,8-bis-(5-bromothiophene-2-yl)-

benzo[1,2,5] thiadiazole as donor unit having HOMO and LUMO energy level of -5.24 eV

and -3.48 eV, respectively. This copolymer showed a strong absorption band in 590-800 nm

(Fig.2). The energy levels of copolymer P are well matched with the CH3NH3PbI3 (conduction band and valance band edge were about -3.92 and -5.96 eV, respectively) for

efficient charge separation. The valance band of this perovskite is lower than the HOMO of

conjugated polymer P. Additionally, conduction band of CH3NH3PbI3 is sufficient higher

than that of the TiO2 and lower than LUMO of P. Hence, this copolymer P may promote

charge transport in the hybrid solar cells, when used as HTM.

Fig. 4 shows the current-voltage (J-V) characteristics of the devices with and without

P3HT and P as HTM, under illumination AM1.5 (100 mW/cm2) and the photovoltaic

parameters are summarized in table 1. The cell with P as HTM, shows a PCE of 6.64 % with

Jsc = 11.98 mA/cm2, Voc = 0.84 V and FF = 0.66, where as P3HT as HTM based cell

exhibited a PCE of 4.24% with Jsc = 11.83 mA/cm2, Voc= 0.64 V and FF = 0.56. As can be

seen from figure and table 1, the cell fabricated without HTM also exhibit relatively good

photovoltaic response (Jsc =9.22 mA/cm2, Voc=0.62 V and FF= 0.48 and PCE = 2.74 %),

though it is inferior to the cells with HTM due to decrease in the Jsc, Voc and FF. This

confirms that photogeneration of charge carrier occurs at the TiO2/CH3NH3PbI3

heterojunction24 and the device acts as p-n junction solar cell. In this device, CH3NH3PbI3

acts simultaneously the roles of both light harvester and hoe transporter. Moreover, the

ACCE

PTED

MAN

USCR

IPT

interface between perovskite/ HTM is beneficial to the hole transfer and leading to the higher

value of Jsc and FF.

As can be seen from the absorption spectra of P3HT and P that these HTM exhibit

absorption peak at 520 nm and 595 nm respectively. The IPCE spectra of the devices based

with P3HT and P HTM and without HTM are shown in Fig. 5. The spectral overlap between

the HTM and perovskite often reduces the light harvesting efficiency of the perovskite and

thus loss in the photocurrent of the device. The IPCE spectra of the devices closely matched

with the absorption spectra of the perovskite, indicating that in spite of the absorption peak of

P3HT and P are about 520 nm and 595 nm, respectively, the polymers does not contribute to

the photocurrent. Moreover, the similar shape of IPCE spectra for both devices attributed that

light absorption by the polymer is negligible and the role of these polymers is limited to the

charge transporting layer. The cell with P yields relatively higher IPCE values at most of the

wavelengths than the cell with P3HT. This finding is consistent with the slightly higher value

of Jsc for former device, obtained from J-V characteristics, under illumination.

The value of Jsc for device based on P is slightly higher than that for P3HT counter

part, whereas Voc and FF are significantly higher the device based on P. It is reported that the

Voc of a hybrid solar cell is closely related to the difference between the quasi Fermi level of

electrons in TiO2 (n-type semiconductor), under illumination and HOMO level of the p-type

HTM. The conjugated copolymer P has a HOMO energy level of -5.24 eV is deeper than that

of P3HT (-5.1 eV), resulting higher value of Voc for the cell based on P as HTM. The

difference in the HOMO level of P and P3HT is only about 0.14 eV, but the difference in the

Voc is about 0.20 V. Therefore, the Voc may be attributed to the charge recombination

kinetics. The J-V characteristics of the devices in dark (Fig. 6) can give the information of

charge recombination kinetics in the device. As shown in Figure the device with P has

relatively lower dark current and an upper shift in onset, compared to P3HT. This implies that

P has a superior electron blocking ability than P3HT. Since the dark current is the measure of

the recombination current. The small dark current means reduction in the back electron

recombination. This reduction pushes the quasi Fermi level of TiO2 upwards (more negative),

thereby enlarging the difference between the HOMO of P and quasi Fermi level of TiO2,

resulting contribution to the enhancement in Voc. Moreover, the high value of Voc for P as

compared to P3HT is in agreement with the relative difference in the HOMO levels of P and

P3HT because the energy level offset between the HOMO level of donor (HTM) and the

LUMO level of acceptor (perovskite) modulates the magnitude of Voc.

ACCE

PTED

MAN

USCR

IPT

It is worth noting that the Jsc of the P based cell is slightly higher than that for P3HT

despite of small energetic driving force of regeneration of oxidized perovskite for former

device as compared P3HT. Since a driving force of 0.30 mV is sufficient for the regeneration

of oxidized perovskite, the off set between the HOMO level of P and valance band edge of

perovskite is sufficient for regeneration but lower than that for device based on P3HT. As the

back charge recombination for device based on P is suppressed, we explain the slight increase

in Jsc by assuming that slow regeneration rate (transfer of electron from P to perovskite) was

compensated by the fast charge transport in P HTM medium as compared to P3HT. The

difference in the FF can be understand with the assumptions described by Burschka et al.,

who demonstrated that the conductivity (charge carrier mobility) of an organic semiconductor

is important for achieving a high photovoltaic performance of the device.25 We have

measured the charge carrier mobility by fitting J-V characteristics in dark with space charge

current limited model. The hole mobility of P is about 6.68 x10-4 cm2/Vs which is higher than

that for P3HT (2.45 x10-4 cm2/Vs). Therefore, the P exhibited a higher conductivity than

P3HT indicates that conjugated polymer P facilities hole transport more efficiently that

P3HT.26 The FF is related to the series resistance (Rs) and shunt resistance (Rsh). In order to

obtain a high FF solar cell should exhibits a low Rs and high Rsh. The main difference in the

devices investigated here is the HTM. This means that the FF value can be partly ascribed to

the increased hole transporting and electron blocking ability of HTM, which could suppress

the possibility for the photogenerated charges to recombine before they reach to the

collecting electrode. Moreover, the space charge effect in reduced in the TiO2/perovskite/P

junction as compared to the TiO2/perovskite/P3HT junction due to the small difference in the

mobility between electron and hole. It can be also seen from the J-V characteristics under

illumination, the series resistance (reciprocal of slope of J-V characteristics at Voc) is lower

for the device with P as compared to P3HT counterpart also consistent with the fact that the

hole mobility for P is higher than that for P3HT. The higher value of FF for solar cell with P

compared to P3HT counterpart may be ascribed to the reduced series resistance and fast

charge transport. Moreover, the space charge effect in reduced in the TiO2/perovskite/P

junction as compared to the TiO2/perovskite/P3HT junction due to the small difference in the

mobility between electron and hole, resulting balanced charge transport6,27 leading to an

increase in the FF and PCE.

4. Conclusion In summary, we have fabricated a solid state organic-inorganic hybrid solar cells

based on a CH3NH3PbI3 perovskite as light harvester and P3HT and D-A conjugated

ACCE

PTED

MAN

USCR

IPT

copolymer P as hole transporting materials. The solar cell based on P showed a considerable

higher performance than that for P3HT. The Jsc of the solar cell based on P is slightly higher

than that for P3HT, but improvement in PCE was attributed to the mainly due to the

enhanced Voc and FF.

Acknowledgment

We are thankful to Prof. M.L. Keshtov, Institute of Organoelement Compounds of the

Russian Academy of Sciences, Vavilova, Moscow, for providing the copolymer. We are also

thankful to Dr. S. Biswas, Department of physics, LNMIIT, Jaipur for providing the facilities

for device fabrication and their characterization. PN thanks to CSIR for providing senior

research fellowship. SPS thanks to XII FY CSIR-INTELCOAT (CSC0114) for financial

support.

References

1. ORegan, B.; Grtzel M. A Low-cost, High Efficiency Solar Cell Based on Dye-Sensitized Colloidal TiO2 Films. Nature 1991, 353, 737740.

2. Yella, A.; Lee, H. W.; Tsao, H. N.; Yi, C.; Chandiran, A. K.; Nazeeruddin, M. K.;

Diau, E. W.; Yeh, C. Y.; Zakeeruddin, S. M.; Grtzel, M. Porphyrin-Sensitized Solar Cells with Cobalt (II/III)-Based Redox Electrolyte Exceed 12% Efficiency. Science 2011, 334, 629634.

3. Li, L. L.; Diau, E. W. Porphyrin-Sensitized Solar Cells. Chem. Soc. Rev. 2013, 42,

291304.

4. (a) Kojima A.; Teshima K.; Shirai Y.; Miyasaka T. Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells. J. Am. Chem. Soc. 2009, 131, 6050. (b) Singh, S. P.; Nagarjuna, P. Organometal Halide Perovskites as Useful Materials in Sensitized Solar Cells. Dalton Trans. 2014, 43, 5247-5251.

5. Im, J. H.; Lee, C. R.; Lee, J. W.; Park, S. W.; Park, N. G. 6.5% Efficient Perovskite

Quantum-Dot-Sensitized Solar Cell. Nanoscale 2011, 3, 4088-4093.

6. Kim, H. S.; Lee, C. R.; Im, J. H.; Lee, K. B.; Moehl, T.; Marchioro, A.; Moon, S. J.; Baker, R. H.; Yum, J. H.; Moser, J. E.; Grtzel, M.; Park, N. G., Leadiodide Perovskite Sensitized all Solid-State Submicron Thin Film Mesoscopic Solar Cell with Efficiency Exceeding 9% Sci. Rep. 2012, 2, 591.

7. Lee, M. M.; Teuscher, J.; Miyasaka, T.; Murakami, T. N.; Snaith, H. J. Efficient

Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites. Science 2012, 64, 338.

8 Ball, J. M.; Lee, M. M.; Hey, A.; Snaith, H. J. Low-Temperature Processed Meso-

Superstructured to Thin-Film Perovskite Solar Cells. Energy Environ. Sci. 2013, 6, 17391743.

ACCE

PTED

MAN

USCR

IPT

9 Noh, J. H.; Im, S. H.; Heo, J. H.; Mandal, T. N.; Seok, S. I. Chemical Management for

Colorful, Efficient, and Stable Inorganic-Organic Hybrid Nanostructured Solar Cells. Nano Lett. 2013, 13, 17641769.

10 Burschka, J.; Pellet, N.; Moon, S. J.; Humphry, B. R.; Gao, P.; Nazeeruddin, M. K.;

Grtzel, M. Sequential Deposition as a Route to High-Performance Perovskite-Sensitized Solar Cells. Nature 2013, 499, 316319.

11 Jae, H. R.; Chih, C. C.; Eric, W. D. A Perspective of Mesoscopic Solar Cells Based on

Metal Chalcogenide Quantum Dots and Organometal-Halide Perovskites. NPG Asia Materials 2013, 5, 68.

12 Park, N.G. Organometal Perovskite Light Absorbers Toward a 20% Efficiency Low-

Cost Solid-State Mesoscopic Solar Cell. J. Phys. Chem. Lett. 2013, 4, 24232429.

13 (a) Coffey D. C.; Larson, B. W.; Hains, A. W.; Whitaker, J. B.; Kopidakis, N.; Boltalina, O. V.; Strauss, S. H.; Rumbles, G. An Optimal Driving Force for Converting Excitons into Free Carriers in Excitonic Solar Cells. J. Phys. Chem. C. 2012, 116, 8916, (b) Braunecker, W. A.; Oosterhout, S. D.; Owczarczyk, Z. R.; Larsen, R. E.; Larson, B. W.; Ginley, D. S.; Boltalina, O. V.; Strauss, S. H.; Kopidakis, N.; Olson, D. C. Ethynylene-Linked Donor-Acceptor Alternating Copolymers. Macromolecules 2013, 46, 3367.

14 Shin, S. S.; Kim, J. S.; Suk J.H.; Lee K. D.; Kim D. W.; Park J. H.; Cho I. S.; Hong

K.S.; Kim J. Y. Improved Quantum Efficiency of Highly Efficient Perovskite BaSnO3-based Dye Sensitized Solar cells, ACS Nano 2013, 7, 1027-1035

15 Abrusci, A.; Stranks, S. D.; Docampo, P.; Yip H. L.; Jen, A. K. Y.; Snaith, H. J. High-

Performance Perovskite-Polymer Hybrid Solar Cells via Electronic Coupling with Fullerene Monolayers. Nano Lett. 2013, 13, 31243128.

16 Conings, B.; Baeten, L.; Dobbelaere, C. D.; DHaen, J.; Manca, J.; Hans-Gerd, B.

Perovskite-Based Hybrid Solar Cells Exceeding 10% Efficiency with High Reproducibility Using a Thin Film Sandwich Approach. Adv. Mater. 2014, 26, 20412046.

17 Cai, B.; Xing, Y.; Yang, Z.; Wen-Hua, Z.; Jieshan, Q. High Performance Hybrid Solar

Cells Sensitized by Organolead Halide Perovskites. Energy Environ. Sci. 2013, 6, 14801485.

18 Heo, J. H.; Im, S. H.; Noh, J. H.; Mandal, T. N.; Lim, C. S., Chang, J. A.; Lee, Y. H.;

Kim, H. J.; Sarkar, A.; Nazeeruddin, M. K.; Grtzel, M.; Seok, S. I. Efficient InorganicOrganic Hybrid Heterojunction Solar Cells Containing Perovskite Compound and Polymeric Hole Conductors. Nat. Photonics 2013, 7, 486491.

19 Bi, D. Q.; Yang, L.; Boschloo, G.; Hagfeldt, A.; Johansson, E. M. J. Effect of Different Hole Transport Materials on Recombination in CH3NH3PbI3 Perovskite-Sensitized Mesoscopic Solar Cells. J. Phys. Chem. Lett. 2013, 4, 15321536.

ACCE

PTED

MAN

USCR

IPT

20 Keshtov, M. L.; Marochkin, D. V.; Kochurov, V. S.; Khokhlov, A. R.; Koukaras, E. N.; Sharma, G. D. New Conjugated Alternating Benzodithiophene-Containing Copolymers with Different Acceptor Units: Synthesis and Photovoltaic Application. J. Mater. Chem. A 2014, 2, 155171.

21 Amalie, D.; Nicolas, T.; Thomas, M.; Peng Gao.; Nazeeruddin, M. K.; Grtzel, M.

Effect of Annealing Temperature on Film Morphology of OrganicInorganic Hybrid Pervoskite Solid-State Solar Cells. Adv. Funct. Mater. doi: 10.1002/adfm.201304022.

22 Jun, Y. J.; Yi, F. C.; Mu, H. L.; Shin, R. P.; Tzung, F. G.; Peter, C.; Ten, C. W. CH 3

NH3 PbI3 Perovskite/Fullerene Planar-Heterojunction Hybrid Solar Cells. Adv. Mater. 2013, 25, 37273732.

23 Chang, J. A.; Rhees, J. H.; Im, S. M.; Lee, Y. H.; Kim, H. J.; Seok, S. I.; Zazeeruddin,

M. K.; Grtzel M. High-Performance Nanostructured Inorganic-Organic Heterojunction Solar Cells. Nano. Lett. 2010, 10, 26092612.

24 Etgar L.; Gao, P.; Xue, Z.; Peng, Q.; Chandiran, A. K.; Liu, B.; Nazeeruddin, M. K.;

Grtzel, M. Mesoscopic CH3NH3PbI3/TiO2 Heterojunction Solar Cells. J. Am. Chem. Soc. 2012, 134, 1739617399.

25 Burschka, J.; Dualeh, A.; Kessler, F.; Baranoff, E.; Cevey-Ha, N. L.; Yi, C. Y.;

Nazeeruddin, M. K.; Grtzel, M. Tris(2-(1H-pyrazol-1-yl)Pyridine)Cobalt(III) as p-type Dopant for Organic Semiconductors and Its Application in Highly Efficient Solid-State Dye-Sensitized Solar Cells. J. Am. Chem. Soc. 2011, 133, 18042-18045.

26 (a) Snaith, H. J.; Grtzel, M. Enhanced Charge Mobility in a Molecular Hole

Transporter via Addition of Redox Inactive Ionic Dopant: Implication to Dye-Sensitized Solar Cells. Appl. Phys. Lett. 2006, 89, 262114, (b) Scholin, R.; Karlsson, M. H.; Eriksson, S. K.; Siegbahn, H.; Johnsson, E. M. J.; Rensmo, H. Energy Level Shifts in Spiro-OMeTAD Molecular Thin Films When Adding Li-TFSI. J. Phys. Chem. C 2012, 116, 2630026305.

27 L. J. A. Koster, V. D. Mihailetchi, H. Xie and P. W. M. Blom, Appl. Phys. Lett., 2005,

87, 203502 Table 1 Photovoltaic performance of devices

Jsc (mA/cm2) Voc (V) FF PCE

Without HTM 9.22 0.62 0.48 2.74

P3HT 11.83 0.64 0.56 4.24

P 11.98 0.84 0.66 6.64

ACCE

PTED

MAN

USCR

IPT

Fig. 1 Chemical structure of D--A conjugated copolymer P and P3HT

Fig. 2 Normalized absorption spectra of CH3NH3PbI3, P and P3HT AC

CEPT

ED M

ANUS

CRIPT

Fig. 3 XRD pattern of CH3NH3PbI3 film

Fig. 4 Current voltage characteristics of the device using P, P3HT HTM and without HTM, under illumination (100 mW/cm2) AC

CEPT

ED M

ANUS

CRIPT

Fig. 5 IPCE spectra of solar cells with P and P3HT HTMs and without HTM

Fig. 6 Current voltage characteristics of the device in dark using P and P3HT as HTM

ACCE

PTED

MAN

USCR

IPT

TOC

CH3NH3PbI3 Perovskite Sensitized Solar Cells Using a D-A Copolymer as Hole Transport Material P. Nagarjuna, K. Narayanaswamy, T. Swetha, G. Hanumantha Rao, Surya Prakash Singh and G. D. Sharma

ACCE

PTED

MAN

USCR

IPT