TOC Graphics
Fully air-printed perovskite solar cell incorporating a nanometer-thick blade coated
bathocuproine (BCP) buffer layer (ITO/PEDOT:PSS/CH
3
NH
3
PbI
3
/PCBM/BCP/Ag).
The BCP layer was blade coated for the first time being also printed in humid air (RH
<50%), and PSCs delivered a PCE of 14.9% proving its compatibility with S2S and R2R
manufacturing.
Efficient Fully Blade-coated Perovskite Solar Cells in Air with
Nanometer-thick Bathocuproine Buffer Layer
Sergio Castro-Hermosa
a,b,c,
*
,+
, Luana Wouk
a
, Izabela Silva Bicalho
a
, Luiza de Queiroz
Corrêa
a
, Bas de Jong
d,e
, Luciò Cinà
d
, Thomas M Brown
b
, Diego Bagnis
a,+
a
CSEM Brasil, Avenida José Cândido da Silveira, 2000, 31035-536, Belo Horizonte,
Brazil
b
CHOSE (Centre for Hybrid and Organic Solar Energy), Department of Electronic
Engineering, University of Rome Tor Vergata, Via del Politecnico 1, 00133 Rome, Italy
c
Hydro Engineering and Agricultural Development Research Group (GHIDA), Faculty
of Engineering, Universidad Surcolombiana, Avenida Pastrana Borrero-Carrera 1,
410001 Neiva, Colombia
d
Cicci Research srl, via Giordania 227, Grosseto 58100, Italy
e
Department of Biotechnology, Chemistry and Pharmacy, University of Siena, Via A.
Moro 2, Siena 53100, Italy
Abstract: Fully printed perovskite solar cells (PSCs) were fabricated in air with all
constituent layers, except for electrodes, deposited by the blade coating technique. The
PSCs incorporated, for the first time, a nanometer-thick printed Bathocuproine (BCP)
hole blocking buffer using blade coating technique and deposited at relative humidity up
to 50%. The PSCs with a p-i-n architecture (Glass/Indium tin oxide(ITO)/poly(3,4-
ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)/CH
3
NH
3
PbI
3
/[6,6]-
*
Lead author: sergio.castro@csembrasil.com.br
+
Corresponding authors: sergio.castro@csembrasil.com.br, diego.bagnis@csembrasil.com.br
phenyl-C
61
-butyric acid methyl ester (PCBM)/BCP/Ag) delivered a maximum power
conversion efficiency (PCE) of 14.9% on an active area of 0.5 cm
2
when measured under
standard test conditions (STC). The PSCs with a blade coated BCP delivered performance
of 10% and 63% higher (in relative terms) than those incorporating a spin coated BCP or
without any BCP film, respectively. The atomic force microscopies (AFM) showed that
blade coated films were more homogeneous and acted also as a surface planarizer leading
to a reduction of roughness which improved BCP/Ag interface reducing charge
recombination. The demonstration of 15% efficient devices with all constituent layers,
including nanometer-thick BCP (~10 nm), deposited by blade coating in air, demonstrates
a route for industrialization of this technology.
Keywords: Perovskite, buffer, bathocuproine (BCP), blade coating, printed electronics.
INTRODUCTION
Perovskite solar cells (PSCs) have achieved remarkable power conversion
efficiencies (PCE) of up to 25.2%[1]; however, these efficiencies have been reached at
the laboratory scale with small-area devices (0.1 cm
2
) fabricated inside high purity
environments (i.e nitrogen glovebox) by highly controllable spin coating technique[2],
and incorporating interlayers and electrodes that are typically thermally evaporated.
Nevertheless, to industrialize the PSCs, both perovskite film and interlayers must be
compatible with low-cost large-scale sheet-to-sheet (S2S) or roll-to-roll (R2R) process
[3], [4]; therefore, PSCs should be fabricated using printing compatible techniques such
as blade and slot-die coating[5]. Blade coating has been widely used in PSCs reaching
efficiencies up to 18.6%[6] when a perovskite active layer was deposited by blade coating
(in air) and the other constituent layers by either spin (inside glovebox) or spray coating
(in air), and 19.6%
[8]
for an all blade coated PSC. Similarly, R2R slot-die deposition[7]–
[9] of PSCs delivered impressive PCEs of 17%[8] and a maximum PCE of 18% with S2S
slot-die deposition[9] when the hole transporting layers were deposited via spin coating.
However, these efficiencies have being reporting for PSC with n-i-p structure which
incorporated thin layers above 30 nm thick. The most challenging issue in both blade and
slot-die deposition is the fast removal of solvent (i.e dimethyl formamide – DMF) while
preventing methylammonium (CH
3
NH
3
) evaporation, to avoid the presence of large grain
boundaries[10] where usually the PbI
2
may remain[11]. This issue has been solved by
replacing the DMF with high boing solvents such as dimethyl sulfoxide (DMSO) or γ-
Butyrolactone (GBL)[12], [13], or replacing the perovskite precursors including the
commonly used PbI
2
. PbI
2
has been replaced with lead acetate (Pb(C
2
H
3
O
2
)
2
) or lead
chloride (PbCl
2
) obtaining very reproducible pinhole free films[14]–[19]. Lead acetate
based PSCs can be fabricated even in high humidity environment representing and
advantage for fabrication and up-scaling[20]. Moreover, the presence of chlorine
improves the growth of perovskite by increasing the crystal growth rate and reducing the
annealing time[6]. The morphology of perovskite has been also modified and controlled
by the drying of wet films by gas quenching [21]–[23]. Perovskite films deposited by
blade or slot-die without gas quenching presented high density of pinholes induced for
the vertical/columnar growth of crystals resulting in a very low absorbance; however,
when a temperature gradient was created by a flow of hot dry air, the growth of perovskite
was horizontal leading to compact and smooth films[22]. Similar results were noted when
perovskite was dried with nitrogen[21]. Thus, gas quenching/drying secured very smooth
pinhole-free perovskite films which are optimal for solar cell fabrication since low
roughness at the surface results in low charge recombination enhancing the PCE of
PSC[24]–[26]. Once the perovskite deposition is optimized using large scale techniques,
the deposition of nanometer-thick interlayer films becomes the main issue to be resolved
since these interlayers reduce charge recombination but they must be compact and
nanometer-thick <10 nm[27]–[30]. Generally, the interlayers are placed between the
electron transporting layer (ETL) and either the perovskite film or metal electrode (gold,
silver or copper depending the implemented solar cell architecture, i.e n-i-p or p-i-n
respectively). Films including MgO[29] or Al
2
O
3
[30], or bathocuproine (BCP) film have
been successfully implemented as interlayer for PSCs. PSCs incorporating BCP by spin
coating or thermal evaporation have reach performances up to 20% and 22% respectively.
Huang group has shown high PCE (~22% in an active area of 0.1 cm
2
[31], [32]) when
both ETL and BCP were thermally evaporated. However; either spin coated in an inert
atmosphere (i.e N
2
or Ar glovebox [33]–[36]) or thermal-evaporated[37], [38] in vacuum
are incompatible processes with R2R manufacturing. Therefore, we present an inverted
PSC with all constituent layers, except for electrodes, deposited by blade coating in air at
35-50% relative humidity (RH). The fully printed PSCs possess a p-i-n architecture, i.e.
Glass/Indium tin oxide(ITO)/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate
(PEDOT:PSS)/CH
3
NH
3
PbI
3
/[6,6]-phenyl-C
61
-butyric acid methyl ester
(PCBM)/BCP/Ag, incorporating a nanometer-thick blade coated bathocuproine buffer
which acts as hole blocking layer(HBL), to reduce the charge accumulation and
recombination at the PCBM/Ag interface[28]. The BCP layer was blade coated for the
first time being also printed in air atmosphere. Fully printed PSCs delivered a maximum
PCE of 14.9% proving its compatibility with S2S and R2R manufacturing.
