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While solar energy holds the promise of long-term sustainable energy, current systems are too inefficient to make mass installations financially viable.
Most solar energy costs originate from the price of installing the panels and the land they sit on. The cells themselves only contribute approximately 20 percent of the cost of solar energy. Due to this, researchers have been attempting to help improve the efficiency of the cells, so that less land may be used to generate electricity from the sun.
Efficiency Improvements on Perovskite Solar Cells
Perovskite solar cells are potentially the most promising solar power technology for researchers right now. First appearing in 2009 with an efficiency of just 3.8 percent, engineers around the world have been developing new ways to increase its energy conversion efficiency.
In April, researchers from Hong Kong Polytechnic University announced the development of perovskite-silicon tandem solar cells, with the world's highest conversion efficiency of 25.5 percent.
The study team noted that a calibrated mix of solar cell materials would be ideal for energy absorption because different materials absorb different wavelengths for solar energy. For instance, methylammonium lead tri-halide perovskite and silicon solar cells are a complementary pair. With the perovskite as a top layer, it can collect the short wavelength photons while the bottom silicon layer absorbs long wavelength photons.
The team were able to boost the efficiency of this hybrid cell, in three different steps. To begin with, the team used a low temperature chemical method to lower the impact created by perovskite defects.
Next, the team made a three-layer sandwich of molybdenum trioxide/gold/molybdenum trioxide, rendering it transparent, so light could penetrate to the bottom silicon layer. Finally, a rose petal-like film was placed as the top layer of the solar panel to capture even more light.
The study team said they are continuing to search for ways to refine their cell and facilitate mass fabrication.
Putting the Pressure on Perovskite
At Stanford University, researchers have taken a different approach to perovskite solar cells, applying intense pressure to increase solar absorption.
In a study published in April, Stanford researchers showed how pressure impacts the way hybrid perovskite cells respond to light. To reach their conclusion, the scientists loaded perovskite samples into a high-pressure “anvil” device made up of two opposing diamonds. Each small sample was placed between the diamonds and then compressed at very high pressures.
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The outcomes were obvious, the researchers said in a press release. One sample, which is commonly orange, became a lighter color under pressure, a sign the perovskite was soaking up higher-energy light waves than normal. However, as the stress heightened further, the sample darkened, implying that lower-energy light was then being drawn in.
The Stanford researchers said that their results indicate pressure could be used to manipulate the wavelengths of light a perovskite cell absorbs.
Improving Conventional Photovoltaics
In addition to making progress on state-of-the-art technologies, researchers are still looking for ways to continue boosting the efficiency of conventional photovoltaics.
In August 2015, engineers from the University of California Riverside announced the successful development of a coating that could potentially boost the efficiency of commercial solar cells by around 30 percent.
Conventional solar cells aren’t able to capture the infrared part of the sun’s rays, allowing it to pass right through. However, the newly-developed coating essentially reshuffles the infrared part of solar radiation to allow conventional photovoltaics to harvest this previously untapped energy. The coating takes two infrared photons and combines their energies to make one higher energy photon. This photon is then readily absorbed by conventional photovoltaic cells.
The UC Riverside engineers said this reshuffling of the infrared spectrum could have implications far beyond that of photovoltaics.
References and Further Reading
Perovskite-Silicon Tandem Solar Cells with the Worlds Highest Power Conversion Efficiency
Stanford Scientists Improve Perovskite Solar-Cell Absorbers by Giving Them a Squeeze
New Solar Panel Coating Could Improve Efficiency by More Than 30 Percent
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