Page 10 - North American Clean Energy September October 2015

solar energy

Perovskite Solar Cells – The long and short of it

By Dr. Xiaoxi He

PEROVSKITE PHOTOVOLTAICS are a breath of fresh air in the photovoltaic market.
in humid conditions and forms PbI2 at higher temperatures due to the loss of CH3NH3I.
hey have experienced a remarkable improvement from 2.2% eiciency – how much
he materials degrade in standard environmental conditions, leading to eiciency and
of the light energy is used by the system per unit area - in 2006, (Toin University of performance drops.
Yokohama) to the latest record of 20.1% in 2014 (Korean Research Institute of Chemical Studies shows perovskite solar cells can maintain more than 80% of its initial eiciency

Technology KRICT, according to the latest eiciency records provided by the National after 500 hours, but after 1,000 hours have minimal eiciency.
Renewable Energy Laboratory (NREL) in the US). Perovskites have already surpassed herefore, applications in utility and BIPV will be unfeasible if the stability issue cannot
organic photovoltaics (OPVs) and dye-sensitized solar cells (DSSCs) and are now, at least be solved. Some companies have claimed that glass-on-glass encapsulation will be used so
in terms of eiciency, in the same range as leading thin ilm PVs like cadmium telluride it can solve most of the stability problem and extend the lifetime. But long lifetimes have

(CdTe) and copper indium gallium selenide (CIGS).
not yet been demonstrated with glass encapsulation.
High and rapidly improved eiciencies are not the only advantage of perovskite
solar cells. Flexibility, semi-transparency, tailored form factors, better low-intensity Toxicity
light performance, low potential processing cost, and low material cost are other value he next big concern is toxicity. CHNHPbIcan convert to PbIwhen in contact with
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propositions of perovskite solar cells. It’s no wonder why many companies and research polar solvents such as water. PbI2, moderately water-soluble, is a carcinogen and is banned
institutions are strongly pursuing the technology.
in many countries. Lead-free perovskite solar cells can only achieve an eiciency of about
6% today. hat means, unless new non-toxic material systems or good lexible barriers are
Cost-competitive vs. slim savings
found, the current toxic perovskite system will be diicult to use in consumer electronics

Perovskite solar cells are often compared to CdTe solar cells, which have the lowest applications, where they would otherwise ofer a compelling beneit over other PV
manufacturing cost among thin-ilm photovoltaic technologies. CdTe reported technologies because perovskites could be cheaper and more lexible. For this reason, many
manufacturing costs of US$ 0.54 W-1 (or US$ 72 m-2) in the last quarter of 2013, for an companies chose to sacriice its potential lexibility, as encapsulation in glass can prevent
average eiciency of 13.4%, where "other material” costs (which exclude semiconductor the harm of toxicity. In addition, similar to CdTe systems, recycling is needed when the

materials) are the majority. hose costs include glass sheets, junction boxes, tabbing, lifetime of the PV cell has expired, although extra cost will be added as a result.
encapsulates, sealants, and tempered glass back sheets. here is no large reduction
potential for the price per unit area due to the manufacturing cost limit, which is Lab-to-fab scaling needs investment
predominantly determined by "other material” costs. Outside of the module cost itself, Another diiculty in the scaling-up process is that while perovskite solar cells show

(i.e., other hardware costs such as the balance-of-system costs) perovskite PVs have no high eiciency in a lab with a device size of 10mm x 10mm, the modules used for real
advantage over c-Si cells or other commercial thin-ilm PV cells.
applications will need to be much larger. However, in larger modules, the eiciencies
However, in terms of the semiconductor material cost, the active material cost of drop. For instance, best performing devices generally have a low surface area of < 0.1 cm2.

perovskites can be cheaper due to the lower cost of perovskite materials compared with Eiciency dropped by about 30% from 0.1 cm2 to 1 cm2 cell area, mostly due to ill factor
CdTe. As the eiciency is further improved, the cost-per-watt can be decreased further.
decrease. However, this can be addressed with time.

Hybrid applications come irst
From no-man’s land to relevancy

Perovskite solar cells will not compete with the dominate c-Si cells in the short term due he irony is that the two biggest issues – lifetime and toxicity – work against each other.
to their lack of maturity. Instead, however, perovskite solar cells can be combined with c-Si Short lifetime applications (2-3 years), such as consumer and wearable electronics, would
cells to further increase eiciency. By adding a perovskite solar cell on top of a c-Si cell, the preferably use cheap, lexible PV; however, due to the toxicity, glass-based versions need
total eiciency can be improved to as high as 30%.
to be used which limit the form factor advantage. Even in glass, they would still need to be

In roof integrated installations where space is limited, the way to increase output is to recycled at the end of the product life, which is not very practical for high-volume, low-cost
improve the eiciency. he c-Si PV market is hugely competitive now, which means that electronics. In contrast, long-term ixed installations, such as BIPV, using toxic materials
any improvement in eiciency will help manufacturers distinguish themselves. he strong can be acceptable provided they undergo managed recycling, but here current perovskites
grid-connected market drive explains why most companies working on perovskite solar struggle to work long enough for such applications. Successfully tackling these issues could

cells are targeting the utility market where the panels can be used in rooftop systems or result in a large opportunity for perovskites. Failing to do so may see the opposite.
mounted on the ground.
Perovskite solar technology is still young but has enormous potential. New material
Perovskite solar cells can be integrated into glass and used for building integrated systems, good barriers, better stability, and non-toxic material research work are ongoing.
photovoltaic (BIPV) applications as well. heir use in smart glass may appear as one of the And the bottom line is, those companies addressing some of the aforementioned issues will

early applications of stand-alone perovskite solar cells, its transparency diferentiating it carve out a signiicant market share.
from c-Si roof panels.
In addition, some companies are also targeting consumer electronics, wearables, and Dr. Xiaoxi He is a technology analyst for IDTechEx Research. Established in 1999, IDTechEx
third-world application markets where the lexibility feature is a key added-value.
provides independent market research, business intelligence, and events on emerging technology

Most perovskite companies claim they will have irst module prototypes near 2017, and to clients in over 80 countries. IDTechEx is headquartered in Cambridge UK; additional oices are
enter the market in 2018. However, there are some barriers in the perovskite systems.
in Berlin, Boston and Tokyo.

Stability is the achilles heel
IDTechEx Research | www.idtechex.com
he biggest issue is the stability, or long term durability, of perovskite PVs. For example,
the most common perovskite material used as the absorber is CHNHPbI. It degrades
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