Technological developments
electricity and have the potential to be cells measuring less than ¼ the size of
installed virtually anywhere that either a grain of rice each. The organic solar
direct sunlight or artificial lighting such cells are fabricated using environmentally Overview of the elemental technology
as fluorescent systems emit visible light. friendly hydrogen-carbon based materials enabling the high energy conversion
In contrast, today’s building-integrated and successfully produce electricity, as efficiency
solar and photovoltaic products are limited demonstrated in a peer-reviewed study in 1. Improvement in the quality of heterojunction
to installation on south-facing surfaces, the Journal of Renewable and sustainable of HIT solar cell (single-crystalline silicon
as is the case with currently-available Energy of the American Institute of (c-Si) and amorphous silicon (a-Si)). A
solar materials tested in these newest Physics. heterojunction is a stacked semiconductor
experiments.” The superior optical absorption structure formed by heterogeneous
In a series of new experiments, properties of New Energy’s ultra-small solar materials. In the case of the HIT solar cell,
researchers repeatedly tested New Energy’s cells enables development of an ultra-thin it means the laminated structure formed by
ultra-small solar cells on a 1” x 1” substrate film (only 1/1000th the thickness of a a-Si and c-Si.
against today’s popular solar materials human hair, or 1/10th of a micrometer) The structure of the HIT solar cell is
for their capacity to produce electricity that can be utilized to produce a such that it has a feature that can reduce
under varying artificial light conditions, transparent solar window. In photovoltaic recombination loss of the electrical
mimicking the levels of light exposure in applications such as see-thru windows, element (charged carrier) by surrounding
homes and commercial offices. In every where transparency is a primary concern, the energy generation layer of single
case, New Energy’s solar cells, the smallest today’s thin film solar cells simply cannot thin crystalline silicon (c-Si) with high
reported organic solar cells of their kind in be utilized to produce a transparent solar quality ultra-thin amorphous silicon (a-Si)
the world, exponentially outperformed all window for application in homes, offices, layers. Recombination loss occurs when
of the conventional materials tested. and commercial buildings. the negative electron and positive hole
Under normal office lighting (carriers) that are produced within the
conditions, without the benefit of outside SaNyo develops hIT solar cells with solar cell combine and disappear, causing
natural light from windows, New Energy’s world’s highest energy conversion a loss in the electrical current produced
ultra-small solar cells produced:
efficiency of 23.0%
by the cell and hence a decrease in the
SANYO Electric Co., Ltd. has broken its
overall output of the solar cell. SANYO has
• Almost 2-fold greater output power
own record for the world’s highest energy
recently managed to improve the quality
density than monocrystalline
conversion efficiency in practical size
of the HIT solar cell junction through
silicon, an established commercial
(100 cm
2
or more) crystalline silicon-type
developing a technology for depositing
solar cell material;
solar cells, achieving a efficiency of 23.0%
a higher quality a-Si layer over the c-Si
• More than 8-fold greater output
(until now 22.3%) at a research level for
substrate while protecting the c-Si surface
power density than copper-indium-
its proprietary HIT solar photovoltaic
from being damaged.
selenide, known for its high
cells. (Evaluation results provided by the
The result was an increase in the open
optical absorption coefficients
National Institute of Advanced Industrial
circuit voltage (Voc), or the maximum
and versatile optical and electrical
Science and Technology (AIST), an energy
voltage that can be produced by the solar
characteristics; and
conversion efficiency public certification
cell, from 0.725V to 0.729V.
• More than 10-fold greater output
body.)
power density than flexible thin-
A HIT (Heterojunction with Intrinsic
2. Reduction of optical absorption loss. In
film amorphous-silicon, a popular
Thin layer) solar cell is composed of
the solar cell, sunlight that hits its surface
‘second-generation’ solar thin-film
a single thin crystalline silicon wafer
needs to be guided to the c-Si, the energy
material.
sandwiched by ultra-thin amorphous
generation layer, with the smallest possible
New Energy’s solar cells generate electricity
silicon layers. This product provides
absorption loss. As for the HIT solar cell,
not only from the visible radiation found
industry-leading performance and value
reduction of optical absorption loss in the
in sunlight but also by using the visible
using state-of-the-art manufacturing
a-Si layer, which covers the front and rear
light found in artificial illumination,
techniques. The increase in the solar cell
surfaces of the c-Si, and the transparent
such as the fluorescent lighting typically
conversion efficiency is accompanied
conductive layer was a challenge.
installed in offices and commercial
by significant advances in lowering the
Absorption of short-wavelength solar
buildings. While the majority of today’s
production cost of the photovoltaic
radiation by the a-Si layer and that of
solar cells can only be installed where
system and the reduction in the use of raw
long-wavelength solar radiation by the
direct sunlight is available, New Energy’s
materials such as silicon.
transparent conductive layer were the
cells could be installed close to any source
of visible light.
New Energy’s SolarWindow™
technology makes use of an organic
solar array, which has the same desirable
electrical properties as silicon, yet has a
considerably better capacity to ‘optically
absorb’ photons from light to generate
electricity and achieves transparency
through the innovative use of conducting
polymers. Each solar array is composed
of a series of twenty ultra-small solar
www.globalsolartechnology.com
Global Solar Technology – July/August 2009 – 25
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