Scientists boost stability and efficiency of next-gen solar tech
Solar modules made from perovskite material gain power to transform the
solar tech industry

Date:
July 20, 2020
Source:
Okinawa Institute of Science and Technology (OIST) Graduate
University
Summary:
Researchers have created next-generation solar modules with high
efficiency and good stability. Made using a type of material called
perovskites, these solar modules can maintain a high performance
for over 2000 hours. Their findings have brightened prospects
of commercialization.



FULL STORY ========================================================================== Researchers from the Okinawa Institute of Science and Technology Graduate University (OIST) have created next-generation solar modules with high efficiency and good stability. Made using a type of material called perovskites, these solar modules can maintain a high performance for over
2000 hours. Their findings, reported 20th July 2020 in leading journal,
Nature Energy, have brightened prospects of commercialization.


========================================================================== Perovskites have the potential to revolutionize the solar technology
industry.

Flexible and lightweight, they promise more versatility than the heavy and rigid silicon-based cells currently dominating the market. But scientists
must overcome some major hurdles before perovskites can be commercialized.

"There are three conditions that perovskites must meet: they must be cheap
to produce, highly efficient and have a long lifespan," said Professor
Yabing Qi, head of the OIST Energy Materials and Surface Sciences Unit,
who led this study.

The cost of making perovskite solar cells is low, as the cheap raw
materials require little energy to process. And in just over a decade, scientists have made huge strides in improving how effectively perovskite
solar cells convert sunlight to electricity, with efficiency levels now comparable to those of silicon-based cells.

However, once scaled up from tiny solar cells to larger solar modules,
the efficiency levels of perovskites plummet. This is problematic as
commercial solar technology needs to remain efficient at the size of
solar panels, several feet in length.

"Scaling-up is very demanding; any defects in the material become more pronounced so you need high-quality materials and better fabrication techniques," explained Dr. Luis Ono, a co-author of this study.



==========================================================================
The instability of perovskites is another key issue under intense investigation. Commercial solar cells need to be able to withstand years
of operation but currently perovskite solar cells degrade fast.

Building up the layers Professor Qi's team, supported by the OIST
Technology Development and Innovation Center's Proof-of-Concept
Program, addressed these stability and efficiency issues using a new
approach. Perovskite solar devices are made up of multiple layers --
each with a specific function. Instead of focusing on just one layer,
they looked at the overall performance of the device and how the layers interact with one another.

The active perovskite layer, which absorbs sunlight, lies in the center
of the device, sandwiched between the other layers. When photons
of light strike the perovskite layer, negatively-charged electrons
harness this energy and "jump" to a higher energy level, leaving behind positively-charged "holes" where the electrons used to be. These charges
are then diverted in opposite directions into electron and hole transport layers above and below the active layer. This creates a flow of charge
-- or electricity -- that can leave the solar device via electrodes. The
device is also encapsulated by a protective layer that reduces degradation
and prevents toxic chemicals from leaking into the environment.

In the study, the scientists worked with solar modules that were 22.4 cm2.



==========================================================================
The scientists first improved the interface between the perovskite active
layer and the electron transport layer, by adding a chemical called EDTAK between the two layers. They found that EDTAK prevented the tin oxide
electron transport layer from reacting with the perovskite active layer, increasing the stability of the solar module.

The EDTAK also improved the efficiency of the perovskite solar module
in two different ways. Firstly, potassium in the EDTAK moved into the
active perovskite layer and "healed" tiny defects on the perovskite
surface. This prevented these defects from trapping the moving electrons
and holes, allowing more electricity to be generated. The EDTAK also
increased performance by enhancing the conductive properties of the tin
oxide electron transport layer, making it easier to collect electrons
from the perovskite layer.

The scientists made similar improvements to the interface between
the perovskite active layer and the hole transport layer. This time,
they added a type of perovskite called EAMA between the layers, which
enhanced the ability for the hole transport layer to receive holes.

The EAMA-treated device also showed better stability under humidity and temperature tests. This was due to how the EAMA interacted with the
surface of the perovskite active layer, which is a mosaic of crystal
grains. In solar devices without EAMA, the scientists saw that cracks
formed on the surface of the active layer, which originated from the
boundaries between these grains.

When the scientists added EAMA, they observed that the additional
perovskite material filled the grain boundaries and stopped moisture
from entering, preventing these cracks from forming.

The team also modified the hole transport layer itself, by mixing in
a small amount of polymer called PH3T. This polymer boosted moisture
resistance by providing the layer with water-repellant properties.

The polymer also solved a major issue that has previously hampered
improvements to long-term stability. The electrode on top of the
perovskite solar module is formed from thin strips of gold. But over
time, tiny gold particles migrate from the electrode, through the hole transport layer and into the active perovskite layer. This irreversibly
impairs performance of the device.

When the researchers incorporated PH3T, they found that the gold particles migrated into the device more slowly which significantly increased the
module's lifespan.

For their final improvement, the scientists added a thin layer of
the polymer, parylene, in addition to glass, to provide a protective
coating to the solar module. With this added protection, the solar
modules maintained about 86% of their initial performance, even after
2000 hours of constant illumination.

In collaboration with Dr. Said Kazaoui at National Institute of Advanced Industrial Science and Technology (AIST), the OIST team tested the
improved solar modules and obtained an efficiency of 16.6% -- a very high efficiency for a solar module of that size. The researchers now aim to
carry out these modifications on larger solar modules, leading the way
towards the development of large-scale, commercial solar technology in
the future.


========================================================================== Story Source: Materials provided by Okinawa_Institute_of_Science_and_Technology_(OIST)
Graduate_University. Original written by Dani Ellenby. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Zonghao Liu, Longbin Qiu, Luis K. Ono, Sisi He, Zhanhao Hu,
Maowei Jiang,
Guoqing Tong, Zhifang Wu, Yan Jiang, Dae-Yong Son, Yangyang
Dang, Said Kazaoui, Yabing Qi. A holistic approach to interface
stabilization for efficient perovskite solar modules with over
2,000-hour operational stability. Nature Energy, 2020; DOI:
10.1038/s41560-020-0653-2 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200720112329.htm

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