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Perovskite Solar Cells

JACT Infinity

Today, solar energy resources outnumber human consumption 10,000:1, yet the total solar

energy usage in the United States is a mere .02% (Solar). Solar energy has the resources to be a

dominating technology in the US energy market, but today’s solar technologies lack a LCOE to make

them cost competitive to the current market dominant – coal. As a research team, we analyzed a new

solar technology called perovskite solar cells. The group then compared both perovskite and silicon

based cells to coal. The researched focused on four factors; technology, energy, economics, and

environment. Our research will look at perovskite from the scope of the LCOE, the efficiency of the

technology, the technology itself, the environmental costs and benefits, and the production and

maintenance costs. Solar and coal energy were chosen as competitors because current solar cells are

very similar to perovskite cells and in reference to the fact that coal is the nation’s leading source of

power, the group assumed coal produced energy would make a fair baseline. By showing the similar

characteristics of perovskite with silicon, which is now a household term, the group is able to

communicate the consumer related benefits of perovskite easily. The benefits of perovskite solar cells

produce a product that is cost comparable to silicon cells as well as coal produced energy while being

the cleanest form of energy out of all three.

Technology

Andrew Sciotti

Solar technology has been around in one form or another since the 18th century. Horace de

Saussure created the first solar collector in 1767 (Exploring Green Technology). In our time, Silicon is

primarily used in solar cells. There are two kinds of solar cells, thin film cells and silicon cells. Silicon



cells have been the norm but thin film cells, which uses alternative elements to silicon, are quickly being

improved.

Looking in depth at the solar cell, they are

created using multiple layers of different materials.

In reference to the diagram on the left (NOVA), a

photovoltaic cell contains five layers. The first layer

consists of metallic strips that will connect to the

bottom metallic plating via conductive wires to

create the electric circuit. Below the first layer of

conductive metal is an antireflective coating that

helps trap the light photons in the cell. Below the antireflective coating begins the section of silicon. The

first section of silicon, labeled in red, is usually doped with phosphorous. Because phosphorus has an

excess of electrons, when combined with the silicon, the whole layer becomes negatively charged. This

layer is called the n-type layer because it is negatively charged. The second section of silicon, labeled in

green, is doped with boron. Boron is naturally positively charged and thus when doped in silicon, the

whole layer becomes positively charged. This is called the p-type layer because it is positively charged.

After the two layers are put together in the factory, the electrons from the n-type silicon layer transfer to

the p-type layer. Due to the semiconducting property of silicon, the charge differential is maintained.

This charge differential is what creates a magnetic field. To produce the electricity in the cell, light

photons from the sun are collected by the antireflective layer and those photons hit the excess of

electrons in the bottom layer of silicon. The photons dislodge the electrons and fling them across the

magnetic field, this movement of electrons across the field is what creates electricity. The electricity is



transferred by the metallic layers as well as the conductive wires (NOVA).

Thin film solar cells has been quickly rising in terms of

efficiency and cost effectiveness. Perovskite (found to the right)

(Fabre), an old technology, has been recently implemented in

solar technology. The mineral was found in Russia by Gustav

Rose. While exploring the Ural Mountains in 1839 Gustav came

across perovskite, which has a chemical formula of CaTiO3

(Web Mineral). The mineral uses the silicon based solar

technology but to much better effect. Instead of a thick layer of silicon, perovskite produces the same

results with less material. Silicon cells have a thickness of 150,000 nanometers while perovskite cells are

330 nanometers thick (Physicsworld).

Perovskite has a very simple molecular structure which contributes to the ease of manufacturing.

While Silicon has a complex nanostructure (in reference to the diagram on

the left) due to the crystalline characteristic of the element (Hyperphysics),

perovskite’s nanostructure is very uniform and block-like due to the

manufacturing process (in reference to diagram below) (Steele). Perovskite

layers are produced

via vapor deposition which is the process where

highly stable and uniform solids are created by

placing each molecule of a substance one by one

on a surface. Another benefit of using perovskite



in solar cells is that the infrastructure that currently produces silicon cells can be adapted quickly and

easily to accommodate perovskite. By doing so, there is an elimination for the need of new infrastructure

and specialized factories to produce perovskite solar cells.

Energy Julian Harley

Perovskite cells will work like any other photovoltaic cell meaning that when looking at the

energy statistics we can see that perovskites are almost as efficient as the silicon cells, but still not as

efficient as coal. The energy from the perovskite solar cell comes from the sun and is transferred into

electricity through the photovoltaic effect. Some of the energy losses along the way come from the fact

that not all of the electrons are transferred between the p-type and n-type perovskites in that comprise

the solar cells. Currently perovskites are less efficient than both silicon solar cells and coal, with a mass

marketed max efficiency of 15 % while silicon has an efficiency of 25%. An ideal efficiency for

perovskites would be greater than 25% which would put it above the level of silicon cells. With an

improvement from a 3.5% efficiency in 2009 to a 15% efficiency now perovskite solar cells have a

strong chance of improving to the ideal efficiency (Yirka, 2013). Our other primary comparison

technology, coal, has an average efficiency of 31% with no signs of immediate improvement

(Euractiv.com 2006). The following chart displays the efficiencies of silicon and perovskite cells along

with the comparison technology of coal. Other technologies are included in the graph in order to help

show that a 25% efficiency such as silicon’s is not low but average.



In terms of energy production coal leads by producing approximately 21 quadrillion BTU’s of

energy per a year compared to the 158 trillion BTU’s produced by solar. For an easier comparison

solar only produces .7 % of the amount of energy produced by coal (Takala 2013). When looking at

the capacity factors of solar panels and coal the latter option continues to prevail with a capacity factor

of 70% while solar panels, only have a capacity factor between 10% and 25%. The main reason the

the small capacity factor for solar panels is the fact that they do not work at night cutting the actual

power generation of solar panels significantly (Ozgur 2013). The chart below displays the capacity

factors of solar panels in comparison to our primary technology of coal and other well known sources of

energy.



Generation Type Capacity Factor

Solar Panels 10-25%

Wind Turbines 25%

Hydroelectric Power Stations 40%

Coal Fired Power Plants 70%

Nuclear Power Plants 89%

Combined Cycle Gas Turbine 38%

*(Source: Sunmetrix-What is capacity factor and how does solar energy compare?)

Although solar may not lead the energy field in efficiency or capacity factor the economic gains

from perovskites will make them the better option in the future.

Economics

Tim Wagner

The economic benefits of perovskite solar energy over that of its comparison technologies are

the heart of what makes perovskite solar cells the most promising solar power to date. The comparison

technology solar energy, seems to be the most marketable option in the new ‘geared for green’ energy

market. Yet, coal-fired power, the other comparison technology is the current market leader in energy

production. The reason for this is coal has the smallest Levelized Cost of Electricity (LCOE) as

reported by the Bloomberg New Energy Finance Model of LCOEs.

“Levelized cost is often cited as a convenient summary measure of the overall competiveness of different

generating technologies. It represents the per-kilowatthour cost (in real dollars) of building and operating a



generating plant over an assumed financial life and duty cycle.”

(Levelized Cost of New Generation Resources)

Under this definition the LCOE’s of the comparison technologies can be shown as:

(Source: U.S. Energy Information Administration, Annual Energy Outlook 2013, December 2012, DOE/EIA-0383(2012))

This model demonstrates current market analysis of energy technologies. It is the most

quantitative and current data available on the three energy technologies. Even so, it only shows the

comparison technologies. Perovskite solar energy does not have any quantitative LCOE data yet

because they are still in the development phase of production. Some researchers estimate an LCOE of

0.10-0.20 $/kwh. (Bullis,2013) That projected LCOE would be cost competitive with coal’s 0.08

$/kwh.

Projecting LCOE comparisons for the researched technologies proved difficult for several

reasons. The solar market is on both commercial and residential levels. Focusing on the commercial

models only, research found that, while solar energy has a significantly higher LCOE, the cost has

lowered dramatically over the past 30 years. This is because of Swanson’s law, a modified version of



Moore’s law named after Richard Swanson, founder of SunPower. Swanson’s law takes what

Moore’s law did for computer technology, and applies it to solar power. Swanson’s law states that the

LCOE of solar power drops by 20% every time the manufacturing capacity doubles.

(Pethokoukis,2013)

What this does is create a curve that affirmly predicts the LCOE of all solar power is going to continue

to go down in the up and coming years.

Swanson’s law represents solar as a whole, but it actually benefits perovskite cells more that

silicon based PV. This is because silicon is more expensive to mine than it is to obtain perovskite. Also,

the perovskite cells can be made in manufacturing facilities that were previously used for silicon cells,

which creates a significantly lower LCOE. (Phys.org, 2013)

The coal-fired power market is strictly commercial. Focusing on this market, research found



that the capacity factor is the highest of all power sources used in the US. This, and because there aren’t

any new plants in production, are the main contributors as to why the LCOE of coal power is lowest on

market. Although, unlike solar, the future does not look as promising for coal. Most researches believe

coal has reached its peak. In fact, many scientists cite 2008 to be the year that coal production peaked

in the U.S. (Levelized Cost of New Generation Resources)

Coal energy production is still the dominant of the market, and will continue to dominate the

market until other technologies are able able to take the energy production load off of this

non-renewable resource for the same LCOE or lower. Perovskite solar cells will do this once they are

ready for market.

EnvironmentCollin Dunnington

Compared to the leading energy source, coal, solar energy is incredibly more environmentally

efficient. Although coal provides 44% of electricity in the U.S., it is the nastiest source of energy known



to man. Coal plants lead the nation in carbon dioxide emissions by producing on average 1.7 billion tons

of CO2 every year (Environmental Impacts). Not only is this destroying the ecosystem, it is having a

direct effect on the lives of so many families. Perovskite, a new and coming solar energy, is cleaner than

coal and even cleaner than the standard solar energy method, silicon cells. Mining for silicon is a dirty

process. Not only are fuels consumed to extract the silicon but the transportation of the silicon

contributes to the air pollution (Silica Sand Mining). Unlike silicon, perovskite is chemically structured,

thus eliminating the mining and transportation process. Perovskite is the most environmentally friendly

development in the history of solar energy, but even this has a problem. The lead (Pb) used in

perovskite solar cells, and also silicon cells, is toxic to the environment. Fortunately, scientists have

proposed that an alternative, such as tin, may be a possibility (Bullis). If this substitution can be made

possible along with proper recycling of used panels, perovskite solar energy can become the cleanest

energy provider in science.

Perovskite solar cells offer the consumer a better option to both silicon based solar cells and

coal-fired power. Perovskite is environmentally friendly in comparison because coal is a huge pollutant

which is trademarked by the billowing smokestacks. The technology is a better alternative to solar cells

because silicon mining is a very dirty process that causes momentous and irreversible damage to the

Earth. Perovskite is cutting edge due to the chemically structured layers that are designed to be smaller

and more efficient than silicon cells. Also, it is highly durable which solves the long-standing problem

with thin film cells. The technological advancements for perovskite have lead to a projected LCOE

nearly the same as coal’s LCOE. The improvements in solar power due to technological advancements

like perovskite back Swanson’s law and demonstrate that it costs will continue to decrease yearly.



Also, the research done on coal shows that it has surpassed it’s peak power, meaning the market will

have more room for perovskite solar power. Perovskites low LCOE and marketable greenness will

encourage companies to invest in this new technology.

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