www.sciencemag.org/cgi/content/full/science.aam6620/DC1

Supplementary Materials for

Colloidally prepared La-doped BaSnO3 electrodes for efficient, photostable perovskite solar cells

Seong Sik Shin, Eun Joo Yeom, Woon Seok Yang, Seyoon Hur, Min Gyu Kim, Jino Im,

Jangwon Seo, Jun Hong Noh,* Sang Il Seok*

*Corresponding author. Email: seoksi@unist.ac.kr (S.I.S.); jhnoh@krict.re.kr (J.H.N.)

Published 30 March 2017 on Science First Release DOI: 10.1126/science.aam6620

This PDF file includes:

Materials and Methods Figs. S1 to S11 References

Materials and Methods

Synthesis of BSO CSMC NPs

All chemicals for the preparation of NPs were of reagent grade and were used without further

purification. All synthetic process was performed in air atmosphere. BaCl2⋅2 H2O (10 mmol;

99%, Aldrich), SnCl4⋅5 H2O (10 mmol; 98%, Aldrich) and C6H8O7 (5 mmol; 99.5%, Aldrich)

were dissolved in hydrogen peroxide aqueous solution (170 mL; 30%, OCI) using constant

stirring. For synthesizing 5 mol% La-doped BSO NPs, La(NO3)3⋅5 H2O (0.5 mmol; 99%,

Aldrich) was introduced into mixture solution of BaCl2⋅2 H2O (9.5 mmol), SnCl4⋅5 H2O (10

mmol) and C6H8O7 (5 mmol). The pH of the reaction solution was adjusted to a value of 10

using ammonia solution (25%, OCI) with constant stirring. The resultant solution was aged at

RT ~ 90°C) for 0 ~ 60 min with a different H2O2 concentration (0 - 30 %). The obtained

products were thoroughly washed with deionized water and ethanol, and were then dispersed

in 2-methoxy ethanol (99.8%, Aldrich), resulting in a colloidal solution.

Solar Cell Fabrication

A F-doped SnO2 (FTO, Pilkington, TEC8) substrates were chemically etched with zinc

powder and dilute HCl solution, and cleaned by sonication in deionized water, acetone, and

ethanol. A dense blocking layer of TiO2 (bl-TiO2, ~70 nm in thickness) was deposited onto a

FTO substrate by spray pyrolysis, using a 20 mM titanium diisopropoxide

bis(acetylacetonate) solution (Aldrich) at 450°C to prevent direct contact between the FTO

and the hole-conducting layer. For BSO and LBSO-based devices, BSO and LBSO thin films

were prepared by spin coating the colloidal dispersion of BSO and LBSO CSMC particles

onto Bl-TiO2-coated FTO glass at 3,000r.p.m. for 30s, followed by calcining on a hot plate at

500°C for 1 h. To control film thickness, the procedure was repeated several times. For TiO2-

based devices, a 150-nm thick mesoporous (mp) TiO2 film was deposited by spin coating for

50 s at 2500 rpm onto the bl-TiO2/FTO substrate using 50 nm particle TiO2 paste diluted in

ethanol and calcinated at 500°C for 1 h in air to remove the organic components. For

perovskite deposition, CH3NH3I (MAI) was first synthesized by reacting 27.86 mL CH3NH2

(40% in methanol, Junsei Chemical) and 30 mL HI (57 wt% in water, Aldrich) in a 250 mL

round-bottom flask at 0°C for 4 h with stirring, respectively. The precipitate was recovered

by evaporation at 55°C for 1 h. MAI were dissolved in ethanol, recrystallized from diethyl

ether, and dried at 60°C in a vacuum oven for 24 h. The prepared MAI powder and PbI2

(99.9985 %, Alfa aesar) for 0.8 M MAPbI3 solution were stirred in a mixture of 2-

Methoxyethanol, Dimethly sulfoxide (DMSO) (99.9%, Aldrich) and gamm-Butyrolactone

(GBL) (99%, Aldrich) (7:3:4 v/v) at 50°C for 10 min. The resulting solution was deposited

onto the prepared BSO film or mp-TiO2 film by a consecutive two-step spin coating process

at 1,000 and 5,000r.p.m. for 10 and 20s, respectively. During the second spin coating step, 1

mL of toluene was poured on the spinning substrate, and then was dried on a hot plate at

100oC for 10min. For hole transporting layer, a solution of poly(triarylamine) (EM index,

Mn=17,500 g mol-1, 15mg in toluene 1.5ml) was mixed with 15ml of a solution of lithium

bistrifluoromethanesulphonimidate (170mg) in acetonitrile (1ml) and 7.5ml 4-tert-

butylpyridine. The resulting solution was spin coated on the CH3NH3PbI3/BSO thin film at

3,000r.p.m. for 30s. All cells were fabricated in air under relative humidity below 25% at

25°C. Finally, an Au counterelectrode was deposited by thermal evaporation. The entire unit

cell size is 25 mm x 25 mm. Four active areas with size of 4 mm x 4 mm were fabricated on

the unit cell by superposing FTO and Au electrodes. Photovoltaic performance was measured

by masking on the active area with a metal mask (0.096 cm2).

Characterization

The crystal structure and phase of the materials were characterized using an XRD (New D8

Advance, Bruker). All XRD measurements for powder and films were performed in air

atmosphere. The morphologies and microstructures were investigated by field emission

scanning electron microscopy (FESEM, SU 70, Hitachi) and atomic force microscopy

(NanostationII, Surface Imaging Systems). The FTIR spectra were recorded on a Bruker

EQUINOX 55 spectrophotometer with samples prepared by the KBr pellet method. The

optical properties of samples were characterized using an ultraviolet–visible

spectrophotometer (UV 2,550, Shimadzu). X-ray photoelectron spectroscopy (XPS) studies

were carried out using a Thermo VG Scientific K-Alpha. The EQE was measured using a

power source (300W xenon lamp, 66,920, Newport) with a monochromator (Cornerstone

260, Newport) and a multimeter (Keithley 2001). The J–V curves were measured using a

solar simulator (Oriel Class A, 91,195A, Newport) with a source meter (Keithley 2,420) at

100 mWcm-2, AM 1.5 G illumination, and a calibrated Si-reference cell certified by the

NREL. The J–V curves were measured by reverse scan (forward bias (1.2 V) - short circuit (0

V)) or forward scan (short circuit (0V) - forward bias (1.2 V)). The step voltage and the delay

time were fixed at 10 mV and 40 ms, respectively. Time-dependent photocurrent and PCE

were measured with a potentiostat (PGSTAT302N, Autolab) under one sun illumination.

X-ray Absorption Spectroscopy (XAS) Measurement

Temperature-dependent in situ Sn K-edge X-ray absorption spectra, X-ray absorption near

edge structure (XANES), and extended X-ray absorption fine structure (EXAFS), were

collected on the BL10C beam line (WEXAFS) at the Pohang Light Source (PLS-II) with top-

up mode operation under a ring current of 350 mA at 3.0 GeV. From the high-intensity X-ray

photons of the multipole wiggler source, monochromatic X-ray beams could be obtained

using a liquid-nitrogen-cooled double-crystal monochromator (Bruker ASC) with available in

situ exchange in vacuum between a Si(111) and Si(311) crystal pair. Sn K-edge X-ray

absorption spectra using Si(311) crystal pair were recorded with transmittance mode using N2

gas-filled ionization chambers (IC-SPEC, FMB Oxford) for the incident and transmitted X-

ray photons. Higher-order harmonic contaminations were eliminated by detuning to reduce

the incident X-ray intensity by ~30%. Energy calibration was simultaneously carried out for

each measurement with reference Sn foil placed in front of the third ion chamber.

Temperature-dependent in situ Sn K-edge XAS experiments were performed with pelletized

samples. A mixture of the initial crystalline phase from the CPC route and boron nitride (BN)

(weight ratio of 1:2) was ground in an agate mortar, pressed into pellet, and fixed in home-

made heating chamber. For temperature-dependent experiment, the temperatures increased

from RT to 200°C with slow heating rate of 0.5°C min-1 in order to observe precisely in situ

structural evolution around Sn for the as-prepared precursor CSMC (taken one spectrum per

5°C) in air atmosphere.

DFT calculations

To model intermediate states in the growth process, structural optimizations of BaSn(O2)6

and BaSn(O2)3 were performed using the DFT calculations. The PBEsol exchange correlation

functional was applied to optimize internal coordinates and lattice parameters. The plane

wave basis set with 550 eV of the cut-off energy and the Projector Augmented Wave method

implemented in the Vienna Ab initio Simulation Package were employed. For k-point

sampling, 5x5x5 regular k-point mesh was used. The model structures accommodate eight

formula units in calculation unit cells. For BaSn(O2)6, the model structure includes eight

octahedron units which consist of Sn and six O2- molecules. The initial configuration contains

eight octahedral and eight Ba atoms with cubic symmetry, but orientation of the eight

octahedral are randomly distributed. For BaSn(O2)3, the model structure of BaSn(O2)3

consists of eight Ba atoms and eight Sn(O2)6 octahedron units, but the octahedron units share

one O2 with the nearest octahedral, and thus charge valence of O2 becomes O22- from charge

neutrality.

Photo-stability test

Light-soaking test were carried out following two different methods on LBSO- and TiO2

solar cells. In the first light soaking test, the unencapsulated devices including organic HTM

and Au were kept in a nitrogen-filled chamber at constant device temperature of 25°C and

constant AM 1.5G illumination using a solar simulator (Oriel Class A, 91,195A, Newport)

for 120 h. In this test, the J-V curves were hourly monitored with a source meter (Keithley

2,420). To exclude the organic HTM and Au effect in light-soaking test, sandwich-type

devices were fabricated by lamination of two half cells (glass/FTO/n-type oxide/MAPbI3 and

MAPbI3/NiO/FTO/glass). The second aging test was performed by keeping the laminated

devices in light-soaking chamber (K3600-MH300, McScience Inc.), and monitoring their

performance in ambient atmosphere under constant AM 1.5G illumination using metal halide

lamp including UV radiation for 1000 h.

Fig. S1. XRD spectra of the as-prepared powder (non-annealed powders) synthesized at 50°C

for 1 h and annealed powder at 200°C for 30 min in air with heating rate of 5 oC/min.

Fig. S2. Photograph of Scaled-up as-prepared powder and its colloidal solution dispersed in

2-methoxyethanol.

Fig. S3. Particle size distribution for as-prepared powder.

Fig. S4. XRD spectra of as-prepared powders (non-annealed powders) synthesized at (A)

various reaction temperature from RT to 90°C (H2O2 concentration and aging time are fixed

at 30% and 1 h, respectively), (B) various H2O2 concentration from 0 to 30% (Temperature

and aging time are fixed at 50°C and 1 h, respectively), and (C) various aging time from 0 to

60 min (H2O2 concentration and temperature are fixed at 30% and 50°C, respectively).

Fig. S5. XRD spectra of LBSO films annealed at various temperature (RT-500°C) for 1 h.

Fig. S6. XRD patterns, and XPS spectra of LBSO and BSO powders annealed in air at

200°C.

As reported, the carrier density of BSO can be easily tuned by doping higher valance state of

ions like La3+(42, 43). In this work, we doped 5 mol% of La ions in the place of Ba sites to

increase the charge carrier density of pure BSO. The XRD patterns (Figure S6 a) of La doped

BSO (LBSO) is cubic and identical with BSO without any peak shift, because the La atoms

10 20 30 40 50 60

o o

oo

o**

No heat

500 oC

2θ (CuKα)

Inte

nsity

(a.u

.)200 oC

*

***

* LBSO

CSMC

o

oo

ooo

o

o FTO

10 20 30 40 50 60

Inte

nsity

(a.u

.)

2θ (CuKα)

BSO

BSO: La

830 840 850 860

La 3d3/2La 3d5/2

BSO: La

BSO

Inte

nsity

(a.u

.)

Binding energy (eV)

don’t induce the conspicuous structural change in the cubic BSO (44). To check the

incorporation of La in the BSO, the X-ray photoelectron spectroscopy (XPS) analysis was

performed. As shown in figure S6b, the two characteristic peaks of La 3d5/2 and 3d3/2 are

detected from LBSO in the comparison of BSO. The spin-orbit peaks for La 3d5/2 and 3d3/2

are doublets due to two bonding states; the bonding and antibonding states between the 3d94f0

or 3d94f0L configuration can lead to the doublet structures (45, 46).

Fig. S7. J-V curves in reverse and forward sweep for LBSO/MAPbI3 PSC.

0.0 0.2 0.4 0.6 0.8 1.0 1.20

5

10

15

20

25

30

Reverse Forward

Curr

ent d

ensit

y (m

A/cm

2 )

Voltage (V)

Fig. S8. Time-resolved PL of MAPbI3, LBSO/MAPbI3, and TiO2/MAPbI3.

0 10 20 300.01

0.1

1

MAPbI3 LBSO TiO2

PL in

tens

ity (a

.u.)

Time (ns)

Fig. S9. J-V curves of undoped BSO and LBSO-cells.

Fig. S10. J-V curves of the laminate cell (glass/FTO/LBSO/MAPbI3/NiO/FTO/glass). The laminate cell shows shows Jsc (22 mA/cm2), Voc (1.05V), and FF (62.3%), yielding initial PCE of 14.4 %. The laminate cell was fabricated by lamination of two half cells (glass/FTO/LBSO/MAPbI3

and MAPbI3/NiO/FTO/glass) in air under relative humidity below 25% at 25°C. The ethanol

solution containing 0.1 M nickel nitrate hexahydrate (Aldrich) was stirred at 70°C for 4 hours

with monoehanolamine (Aldrich) of same mole ratio to Ni2+. The NiO precursor solution was

spin-coated onto an FTO substrate at 2000 r.p.m for 60 sec, and then dried the film at 110°C

for 5 min. The coating procedure was repeated once more, followed by annealing at 280°C

for 1 hour. The two half cells were fabricated by the procedure described in experimental

section. Then, the prepared two half cells were superposed with facing MAPbI3 sides

(glass/FTO/LBSO/MAPbI3 : MAPbI3/NiO/FTO/glass) and then pressed with 50 MPa.

Heaters in both sides were heated to 180°C with heating rate of 50°C/min and the pressure

and temperature were kept for 10 min. The laminate cells were obtained by slowly release the

pressure and temperature.

Fig. S11. Full-spectrum of metal halide lamp for test of long term photo-stability.

References and Notes 1. M. M. Lee, J. Teuscher, T. Miyasaka, T. N. Murakami, H. J. Snaith, Efficient hybrid solar

cells based on meso-superstructured organometal halide perovskites. Science 338, 643–647 (2012). doi:10.1126/science.1228604 Medline

2. H.-S. Kim, C.-R. Lee, J.-H. Im, K.-B. Lee, T. Moehl, A. Marchioro, S.-J. Moon, R. Humphry-Baker, J.-H. Yum, J. E. Moser, M. Grätzel, N.-G. Park, Lead iodide perovskite sensitized all-solid-state submicron thin film mesoscopic solar cell with efficiency exceeding 9%. Sci. Rep. 2, 591 (2012). doi:10.1038/srep00591 Medline

3. A. Kojima, K. Teshima, Y. Shirai, T. Miyasaka, Organometal halide perovskites as visible-light sensitizers for photovoltaic cells. J. Am. Chem. Soc. 131, 6050–6051 (2009). doi:10.1021/ja809598r Medline

4. M. Saliba, T. Matsui, K. Domanski, J.-Y. Seo, A. Ummadisingu, S. M. Zakeeruddin, J.-P. Correa-Baena, W. R. Tress, A. Abate, A. Hagfeldt, M. Grätzel, Incorporation of rubidium cations into perovskite solar cells improves photovoltaic performance. Science 354, 206–209 (2016). doi:10.1126/science.aah5557 Medline

5. W. S. Yang, J. H. Noh, N. J. Jeon, Y. C. Kim, S. Ryu, J. Seo, S. I. Seok, SOLAR CELLS. High-performance photovoltaic perovskite layers fabricated through intramolecular exchange. Science 348, 1234–1237 (2015). doi:10.1126/science.aaa9272 Medline

6. J. H. Heo, S. H. Im, J. H. Noh, T. N. Mandal, C.-S. Lim, J. A. Chang, Y. H. Lee, H. Kim, A. Sarkar, M. K. Nazeeruddin, M. Grätzel, S. I. Seok, Efficient inorganic-organic hybrid heterojunction solar cells containing perovskite compound and polymeric hole conductors. Nat. Photonics 7, 486–491 (2013). doi:10.1038/nphoton.2013.80

7. M. Liu, M. B. Johnston, H. J. Snaith, Efficient planar heterojunction perovskite solar cells by vapour deposition. Nature 501, 395–398 (2013). doi:10.1038/nature12509 Medline

8. O. Malinkiewicz, A. Yella, Y. H. Lee, G. M. Espallargas, M. Graetzel, M. K. Nazeeruddin, H. J. Bolink, Perovskite solar cells employing organic charge-transport layers. Nat. Photonics 8, 128–132 (2014). doi:10.1038/nphoton.2013.341

9. D.-Y. Son, J.-H. Im, H.-S. Kim, N.-G. Park, 11% efficient perovskite solar cell based on ZnO nanorods: An effective charge collection system. J. Phys. Chem. C 118, 16567–16573 (2014). doi:10.1021/jp412407j

10. J. P. Correa-Baena, L. Steier, W. Tress, M. Saliba, S. Neutzner, T. Matsui, F. Giordano, T. J. Jacobsson, A. R. Srimath Kandada, S. M. Zakeeruddin, Highly efficient planar perovskite solar cells through band alignment engineering. Energy Environ. Sci. 8, 2928–2934 (2015). doi:10.1039/C5EE02608C

11. S. S. Shin, W. S. Yang, J. H. Noh, J. H. Suk, N. J. Jeon, J. H. Park, J. S. Kim, W. M. Seong, S. I. Seok, High-performance flexible perovskite solar cells exploiting Zn2SnO4 prepared in solution below 100 °C. Nat. Commun. 6, 7410 (2015). doi:10.1038/ncomms8410 Medline

12. S. S. Shin, W. S. Yang, E. J. Yeom, S. J. Lee, N. J. Jeon, Y.-C. Joo, I. J. Park, J. H. Noh, S. I. Seok, Tailoring of electron-collecting oxide nanoparticulate layer for flexible perovskite

solar cells. J. Phys. Chem. Lett. 7, 1845–1851 (2016). doi:10.1021/acs.jpclett.6b00295 Medline

13. G. Niu, X. Guo, L. Wang, Review of recent progress in chemical stability of perovskite solar cells. J. Mater. Chem. A Mater. Energy Sustain. 3, 8970–8980 (2015). doi:10.1039/C4TA04994B

14. W. Li, W. Zhang, S. Van Reenen, R. J. Sutton, J. Fan, A. A. Haghighirad, M. B. Johnston, L. Wang, H. J. Snaith, Enhanced UV-light stability of planar heterojunction perovskite solar cells with caesium bromide interface modification. Energy Environ. Sci. 9, 490–498 (2016). doi:10.1039/C5EE03522H

15. T. Leijtens, G. E. Eperon, S. Pathak, A. Abate, M. M. Lee, H. J. Snaith, Overcoming ultraviolet light instability of sensitized TiO2 with meso-superstructured organometal tri-halide perovskite solar cells. Nat. Commun. 4, 2885 (2013). doi:10.1038/ncomms3885 Medline

16. S. Guarnera, A. Abate, W. Zhang, J. M. Foster, G. Richardson, A. Petrozza, H. J. Snaith, Improving the long-term stability of perovskite solar cells with a porous Al2O3 buffer layer. J. Phys. Chem. Lett. 6, 432–437 (2015). doi:10.1021/jz502703p Medline

17. H. Tsai, W. Nie, J.-C. Blancon, C. C. Stoumpos, R. Asadpour, B. Harutyunyan, A. J. Neukirch, R. Verduzco, J. J. Crochet, S. Tretiak, L. Pedesseau, J. Even, M. A. Alam, G. Gupta, J. Lou, P. M. Ajayan, M. J. Bedzyk, M. G. Kanatzidis, A. D. Mohite, High-efficiency two-dimensional Ruddlesden-Popper perovskite solar cells. Nature 536, 312–316 (2016). doi:10.1038/nature18306 Medline

18. F. Bella, G. Griffini, J.-P. Correa-Baena, G. Saracco, M. Grätzel, A. Hagfeldt, S. Turri, C. Gerbaldi, Improving efficiency and stability of perovskite solar cells with photocurable fluoropolymers. Science 354, 203–206 (2016). doi:10.1126/science.aah4046 Medline

19. S. Ito, S. Tanaka, K. Manabe, H. Nishino, Effects of surface blocking layer of Sb2S3 on nanocrystalline TiO2 for CH3NH3PbI3 perovskite solar cells. J. Phys. Chem. C 118, 16995–17000 (2014). doi:10.1021/jp500449z

20. S. K. Pathak, A. Abate, P. Ruckdeschel, B. Roose, K. C. Gödel, Y. Vaynzof, A. Santhala, S. I. Watanabe, D. J. Hollman, N. Noel, A. Sepe, U. Wiesner, R. Friend, H. J. Snaith, U. Steiner, Performance and stability enhancement of dye‐sensitized and perovskite solar cells by Al doping of TiO2. Adv. Funct. Mater. 24, 6046–6055 (2014). doi:10.1002/adfm.201401658

21. D. O. Scanlon, Defect engineering of BaSnO3 for high-performance transparent conducting oxide applications. Phys. Rev. B 87, 161201 (2013). doi:10.1103/PhysRevB.87.161201

22. Y. M. Kim, C. Park, U. Kim, C. Ju, K. Char, High-mobility BaSnO3 thin-film transistor with HfO2 gate insulator. Appl. Phys. Express 9, 011201 (2015). doi:10.7567/APEX.9.011201

23. J. Cerdà, J. Arbiol, G. Dezanneau, R. Dıaz, J. Morante, Perovskite-type BaSnO3 powders for high temperature gas sensor applications. Sens. Actuators B Chem. 84, 21–25 (2002). doi:10.1016/S0925-4005(02)00005-9

24. H. J. Kim, U. Kim, H. M. Kim, T. H. Kim, H. S. Mun, B.-G. Jeon, K. T. Hong, W.-J. Lee, C. Ju, K. H. Kim, K. Char, High mobility in a stable transparent perovskite oxide. Appl. Phys. Express 5, 061102 (2012). doi:10.1143/APEX.5.061102

25. W. Zhang, J. Tang, J. Ye, Photoluminescence and photocatalytic properties of SrSnO3 perovskite. Chem. Phys. Lett. 418, 174–178 (2006). doi:10.1016/j.cplett.2005.10.122

26. W. Wang, S. Liang, K. Ding, J. Bi, J. C. Yu, P. K. Wong, L. Wu, Microwave hydrothermal synthesis of MSnO3 (M2+= Ca2+, Sr2+, Ba2+): Effect of M2+ on crystal structure and photocatalytic properties. J. Mater. Sci. 49, 1893–1902 (2014). doi:10.1007/s10853-013-7880-x

27. P. Wadekar, J. Alaria, M. O’Sullivan, N. Flack, T. Manning, L. Phillips, K. Durose, O. Lozano, S. Lucas, J. Claridge, M. J. Rosseinsky, Improved electrical mobility in highly epitaxial La: BaSnO3 films on SmScO3 (110) substrates. Appl. Phys. Lett. 105, 052104 (2014). doi:10.1063/1.4891816

28. G. Pfaff, Wet chemical synthesis of BaSnO3 and Ba2SnO4 powders. J. Eur. Ceram. Soc. 12, 159–164 (1993). doi:10.1016/0955-2219(93)90137-G

29. S. S. Shin, J. S. Kim, J. H. Suk, K. D. Lee, D. W. Kim, J. H. Park, I. S. Cho, K. S. Hong, J. Y. Kim, Improved quantum efficiency of highly efficient perovskite BaSnO3-based dye-sensitized solar cells. ACS Nano 7, 1027–1035 (2013). doi:10.1021/nn305341x Medline

30. C. Huang, X. Wang, Q. Shi, X. Liu, Y. Zhang, F. Huang, T. Zhang, A facile peroxo-precursor synthesis method and structure evolution of large specific surface area mesoporous BaSnO3. Inorg. Chem. 54, 4002–4010 (2015). doi:10.1021/acs.inorgchem.5b00269 Medline

31. See supplementary materials.

32. J. Cerdà, J. Arbiol, R. Diaz, G. Dezanneau, J. Morante, Synthesis of perovskite-type BaSnO3 particles obtained by a new simple wet chemical route based on a sol–gel process. Mater. Lett. 56, 131–136 (2002). doi:10.1016/S0167-577X(02)00428-7

33. S. Sladkevich, V. Gutkin, O. Lev, E. A. Legurova, D. F. Khabibulin, M. A. Fedotov, V. Uvarov, T. A. Tripol’skaya, P. V. Prikhodchenko, Hydrogen peroxide induced formation of peroxystannate nanoparticles. J. Sol-Gel Sci. Technol. 50, 229–240 (2009). doi:10.1007/s10971-008-1800-6

34. A. V. Churakov, S. Sladkevich, O. Lev, T. A. Tripol’skaya, P. V. Prikhodchenko, Cesium hydroperoxostannate: First complete structural characterization of a homoleptic hydroperoxocomplex. Inorg. Chem. 49, 4762–4764 (2010). doi:10.1021/ic100554u Medline

35. G. Pfaff, V. Hildenbrand, H. Fuess, Spectroscopic study of amorphous precursors for alkaline–earth titanates and stannates, J. Mater. Sci. Lett. 17, 1983–1985 (1998). doi:10.1023/A:1006652405086

36. Y. Zhao, B.-T. Teng, X.-D. Wen, Y. Zhao, Q.-P. Chen, L.-H. Zhao, M.-F. Luo, Superoxide and peroxide species on CeO2 (111), and their oxidation roles. J. Phys. Chem. C 116, 15986–15991 (2012). doi:10.1021/jp3016326

37. E. Yazici, H. Deveci, Factors affecting decomposition of hydrogen peroxide, in Proceedings of the XII International Mineral Processing Symposium (IMPS), 6 to 8 Ocober 2010, Cappadocia- Nevsehir, Turkey, O. Y. Gulsoy, S. L. Ergun, N. M. Can, I. B. Celik, Eds. (Hacettepe University, Department of Mining Engineering, 2010), pp. 609–616.

38. N. J. Jeon, J. H. Noh, Y. C. Kim, W. S. Yang, S. Ryu, S. I. Seok, Solvent engineering for high-performance inorganic-organic hybrid perovskite solar cells. Nat. Mater. 13, 897–903 (2014). doi:10.1038/nmat4014 Medline

39. K. K. James, P. S. Krishnaprasad, K. Hasna, M. K. Jayaraj, Structural and optical properties of La-doped BaSnO3 thin films grown by PLD. J. Phys. Chem. Solids 76, 64–69 (2015). doi:10.1016/j.jpcs.2014.07.024

40. M. Saliba, T. Matsui, J.-Y. Seo, K. Domanski, J.-P. Correa-Baena, M. K. Nazeeruddin, S. M. Zakeeruddin, W. Tress, A. Abate, A. Hagfeldt, M. Grätzel, Cesium-containing triple cation perovskite solar cells: Improved stability, reproducibility and high efficiency. Energy Environ. Sci. 9, 1989–1997 (2016). doi:10.1039/C5EE03874J Medline

41. W. Chen, Y. Wu, Y. Yue, J. Liu, W. Zhang, X. Yang, H. Chen, E. Bi, I. Ashraful, M. Grätzel, L. Han, Efficient and stable large-area perovskite solar cells with inorganic charge extraction layers. Science 350, 944–948 (2015). doi:10.1126/science.aad1015 Medline

42. X. Luo, Y. S. Oh, A. Sirenko, P. Gao, T. Tyson, K. Char, S.-W. Cheong, High carrier mobility in transparent Ba1− xLaxSnO3 crystals with a wide band gap. Appl. Phys. Lett. 100, 172112 (2012). doi:10.1063/1.4709415

43. Z. Lebens-Higgins, D. O. Scanlon, H. Paik, S. Sallis, Y. Nie, M. Uchida, N. F. Quackenbush, M. J. Wahila, G. E. Sterbinsky, D. A. Arena, J. C. Woicik, D. G. Schlom, L. F. J. Piper, Direct observation of electrostatically driven band gap renormalization in a degenerate perovskite transparent conducting oxide. Phys. Rev. Lett. 116, 027602 (2016). doi:10.1103/PhysRevLett.116.027602 Medline

44. C. Shan, T. Huang, J. Zhang, M. Han, Y. Li, Z. Hu, J. Chu, Optical and electrical properties of sol–gel derived Ba1–xLaxSnO3 transparent conducting films for potential optoelectronic applications. J. Phys. Chem. C 118, 6994–7001 (2014). doi:10.1021/jp500100a

45. B. Luo, J. Zhang, J. Wang, P. Ran, Structural, electrical and optical properties of lanthanum-doped barium stannate. Ceram. Int. 41, 2668–2672 (2015). doi:10.1016/j.ceramint.2014.10.080

46. A. Nelson, J. Adams, K. Schaffers, Photoemission investigation of the electronic structure of lanthanum–calcium oxoborate. J. Appl. Phys. 94, 7493–7495 (2003). doi:10.1063/1.1627955