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In the past decade, continued technology advances and cost
improvements have made solar PV one of the most dynamic industries
of our time, as it continues to make a significant and growing
contribution to the global energy mix. Technological innovation is
taking place in a context of extreme price competition among solar
manufacturers, which explains the focus of the industry on
decreasing manufacturing costs, increasing efficiencies, and
reducing losses at all segments and stages of the manufacturing
process.
The average efficiency of commercial silicon modules has
improved in recent years, in the range of 0.3-0.4 percentage point
per year. These efficiency gains have taken place in a very
competitive environment, since module prices have fallen more than
70% in just the past six years.
However, since mainstream technologies, such as p-type
passivated emitter and rear cells (PERCs), are slowly reaching
their physical limits of conversion efficiencies, the industry is
increasingly focused both on optimizing new techniques and
innovations and on applying new PV materials and technologies such
as perovskite. A perovskite solar cell (PSC) is a type of solar
cell that includes a cubical perovskite structured compound, which
is the light-harvesting active layer that is mostly based on a
hybrid organic-inorganic lead or tin halide material.
The conversion efficiency of a PSC has been continuously
increasing during the past 10 years. Considering that perovskite
material for solar technology is in the very early stage of
development, the efficiency improvements from 3.8% in 2009 to about
23% in 2018 are a staggering achievement. This efficiency learning
curve is much steeper compared to any other emerging PV
technologies. Although the efficiencies refer to lab efficiencies
and not to mass production commercial cells, they still indicate
that perovskites can have a huge impact on the solar industry.
Perovskites manufacturing
The PSC technology shares many similarities with other so-called
third-generation solar cells. Particularly in terms of cell design
and processes it is very close to dye-sensitized solar cell (DSSC)
and organic solar cell (OSC, or OPV cells). However, the rapid
progress of PSCs can only partially be explained by that
similarity, because each of the mentioned technologies is being
developed independently.
There is more than one process to produce PSC modules. In its
simplest method, PSCs can be manufactured by roll-to-roll coating,
including well-known technologies such as slot die, spray coating,
and ink-jet printing, or through evaporation. This process
essentially eliminates the need for wafer manufacturing and other
related processes used in crystalline silicon (c-Si) cells.
Figure 1: Simplified schematic diagram of slot die
coating
Another advantage of PSC manufacturing is that perovskite can be
used in both single-junction and tandem-junction technologies. The
single-junction technology is the simplest form, relying on a
single layer of perovskite material, which supplies the
photoelectric effect. In that form the PSC can reach conversion
efficiencies of up to 23%. To increase the efficiency to 27% and
beyond, many research institutes and start-ups are at this moment
exploring using a tandem cell, which is a type of multijunction
cell combining the PSC as an additional absorption layer on
standard c-Si cells, or on thin films such as CIGS and CdTe
modules.
Leveraging factors and barriers to
Perovskites
The advantages of perovskite technology are straightforward. The
perovskite materials are relatively cheap, compared with
crystalline silicon, especially monocrystalline p-type and n-type,
since this technology does not require the use of polysilicon,
silver paste, and other materials used in standard c-Si modules. It
can achieve higher efficiencies because of long carrier diffusion
length within the material, and there is a possibility to choose
the color (absorption band) of the panel, because of widely tunable
bandgap of the material. The PSCs can operate with single-junction
and multijunction technologies (with c-Si and thin film), and are
suitable in different applications and segments, such as building
integrated photovoltaics (BIPV), as well as utility-scale solar
plants.
However, the PSC technology still requires further improvements
in several important factors, such as the strong degradation in
presence of moisture, oxygen, UV light, and high temperature; as
well as the toxicity of lead and tin, which are used during
manufacturing, and which can become apparent during operation, and
at end of life.
Another important area of improvement is the cell size. The
mentioned record efficiencies of 18-23% that are constantly
advertised in the news have been achieved with very small cells,
while cells that have a size compatible with actual commercial use
still exhibit much lower efficiencies of 10-12%.
In sum, the technology still must demonstrate that it is ready
to fulfill all requirements and move from research cells tests to
commercial module production.
Figure 2: Analysis and requirements of current PSC
characteristics
Perovskites applications and forecast
PSCs have potentially more advantages than c-Si cells in BIPVs.
It has the ability to have colored cells, the ability to choose
different sizes and the transparency of the panels, as well as
flexible and curved design, PSCs seem to be a more suitable
technology for BIPV applications than c-Si cells, which cannot or
can only partially replicate that factors. Since many BIPV projects
are installed in prestigious buildings, price sensitivity remains
lower than in standard PV installations and therefore more
favorable to the early adoption of PSCs. The application and
competitiveness of PSCs technologies in other rooftop or ground
applications would still require a further development of
materials, targeting much higher efficiencies in tandem or
multijunction structures, and a significant production cost
reduction to reach commercial applications. In our recent
"Perovskite Solar Cells Report" published in January 2020, IHS
Markit forecasts that the industry will be ready for mass
production and commercialization of perovskite cells (in single-
and multijunction architectures) in the next three to five
years.
To date, there are only a few pilot lines producing PSCs and
only a handful of demonstration installations worldwide. The
production capacity of perovskite modules is limited to pilots and
demonstration projects, and IHS Markit estimates the total
installed capacity does not surpass 20-30 MW globally. However,
numerous equipment manufacturers and research institutes are
heavily investing in developing and advancing the technology to
increase conversion efficiencies and improve current challenges
with instability and degradation of perovskite cells. Some
companies have publicly announced they will start commercial
production already in 2020. To illustrate, Saule Technologies for
example, is ramping up at this moment its production lines in
Poland, and Oxford PV is working with equipment supplier Meyer
Burger transfer its tandem cell technology to launch commercial
production during 2020.
Karl Melkonyan is a Senior Research Analyst at IHS
Markit.