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ACKNOWLEDGMENTS
Funding:This work was supported by the National Institutes of Health
(grant R35 GM138373).Author contributions:T.B.H. and C.S.S.
conceived the work and designed the experiments. T.B.H. and M.J.L.
performed all experiments and collected all data. T.B.H. and
C.S.S. analyzed the data and wrote the manuscript. M.J.L. provided
revisions.Competing interests:C.S.S. and T.B.H. are co-inventors
on the application filed by The Ohio State University for US patent
application number 63/308,319 related to this work.Data and
materials availability:All experimental data, analytical procedures,
and copies of spectra are available in the supplementary materials.

SUPPLEMENTARY MATERIALS
science.org/doi/10.1126/science.abo0039
Materials and Methods
Figs. S1 to S22
References ( 51 Ð 74 )
6 January 2022; accepted 19 March 2022
10.1126/science.abo0039

SOLAR CELLS

Organometallic-functionalized interfaces for highly

efficient inverted perovskite solar cells

Zhen Li^1 †, Bo Li^1 †, Xin Wu^1 †, Stephanie A. Sheppard^2 , Shoufeng Zhang^1 , Danpeng Gao^1 ,

Nicholas J. Long^2 *, Zonglong Zhu1,3*

Further enhancing the performance and stability of inverted perovskite solar cells (PSCs) is crucial for their

commercialization. We report that the functionalization of multication and halide perovskite interfaces with an

organometallic compound, ferrocenyl-bis-thiophene-2-carboxylate (FcTc 2 ), simultaneously enhanced the

efficiency and stability of inverted PSCs. The resultant devices achieved a power conversion efficiency of 25.0%

and maintained >98% of their initial efficiency after continuously operating at the maximum power point

for 1500 hours under simulated AM1.5 illumination. Moreover, the FcTc 2 -functionalized devices passed the

international standards for mature photovoltaics (IEC61215:2016) and have exhibited high stability under the

damp heat test (85°C and 85% relative humidity).

P

ower conversion efficiencies (PCEs) as

high as 25.7% have been realized for

single-junction conventional n-i-p perov-

skite solar cells (PSCs), approaching the

PCEs of state-of-the-art crystalline-silicon

solar cells ( 1 – 3 ). Inverted (p-i-n structure) de-

vices, with a deposition sequence of hole-

transport (p), intrinsic (i), and electron-transport

(n) layers, have exhibited greater stabilities

and lifetimes because of their undoped hole-

transporting layers (HTLs) and the forma-

tion of highly crystalline perovskite films ( 4 – 10 ).

Recently, strategies for managing defects and

ion migration in inverted PSCs have further

contributed to device stability. For example,

Chenet al. have used solid-state carbohy-

drazide to modulate the crystallization of

perovskites and fabricate a minimodule that

maintained 85% of its initial PCE under 1-sun

illumination (where 1 sun is defined as the

standard illumination at AM1.5, or 1 kW m−^2 )

for 1000 hours ( 11 ), and Baiet al. have applied

ionic liquids within perovskite films by sup-

pressing ion migration and have fabricated

PSCs that exhibited only ~5% degradation of

device performance under continuous simu-

lated AM1.5 irradiation for >1800 hours ( 12 ).

However, the currently reported operational

lifetime of inverted PSCs under international

standards still lags far behind the 25-year life-

time guarantee for commercialized silicon

solar cells ( 2 , 13 ). Moreover, although syner-

gistic tailoring of grains, defects, and inter-

faces can boost efficiencies to 23.3%, there is

still a lack of strategy that could result in ef-

ficiencies of up to 25% to rival n-i-p PSCs and

silicon solar cells ( 14 – 16 ).

Here, we report highly efficient and stable

inverted PSCs through interface functional-

ization with an organometallic compound,

ferrocenyl-bis-thiophene-2-carboxylate (FcTc 2 ),

that not only provided strong chemical Pb-O

binding to reduce surface trap states but also

accelerated interfacial electron transfer through

the electron-rich and electron-delocalizable

ferrocene units. The improved interface bind-

ing and carrier transport properties of FcTc 2

contribute to superior device stability. The

resulting devices achieved a PCE of 25.0% (with

certified 24.3%) and maintained >98% of their

initial efficiency in long-term operational stab-

ility tests with continuous 1-sun illumination

for >1500 hours. Moreover, the FcTc 2 -treated

devices exhibited excellent stability under damp

heat tests [85°C and 85% relative humidity

(RH)], which have passed the international

standards for silicon solar cells.

Interfaces were functionalized with FcTc 2

by using the inherent carboxylate and thio-

phene groups around the central ferrocene

motif (see Fig. 1A for chemical structure). The

ultraviolet-visible (UV-vis) absorption spectra

of FcTc 2 in solution and as a thin film are

shown in figs. S1 and S2, respectively. The

device configuration is depicted in Fig. 1A, in

which poly(triaryl amine) (PTAA) was the HTL

and C 60 was the electron transfer layer (ETL).

Figure S3 shows the cross-sectional scanning

electron microscopy (SEM) image of a typical

device with a perovskite composition of Cs0.05

(FA0.98MA0.02)0.95Pb(I0.98Br0.02) 3 (where MA and

FA denote methylammonium and formamidi-

nium, respectively) and FcTc 2 surface treatment.

Time-of-flight secondary ion mass spectrometry

(TOF-SIMS) in Fig. 1B demonstrates that most

of the FcTc 2 was located on the surface of the

perovskite film. We used x-ray diffraction

(XRD), top-view SEM, and UV-vis absorp-

tion spectroscopy measurements to study the

crystallinity, morphology, and optical absorption

of perovskite films with and without FcTc 2 treat-

ment (figs. S4 to S6). All of the samples showed

416 22 APRIL 2022¥VOL 376 ISSUE 6591 science.orgSCIENCE

(^1) Department of Chemistry, City University of Hong Kong,
Kowloon 999077, Hong Kong.^2 Department of Chemistry,
Imperial College London, White City Campus, London, UK.
(^3) Hong Kong Institute of Clean Energy, City University of Hong
Kong, Kowloon 999077, Hong Kong.
*Corresponding author. Email: [email protected] (Z.Z.);
[email protected] (N.J.L.)
†These authors contributed equally to this work.
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