Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Can Perovskites and Silicon Team Up to Boost Industrial Solar Cell Efficiencies?

25.03.2015

By developing a way to stack perovskites atop conventional silicon solar cells, a team of MIT and Stanford researchers create “tandem” photovoltaics that may give a boost to traditional silicon solar cells

Silicon solar cells dominate 90 percent of the global photovoltaic market today, yet the record power conversion efficiency of silicon photovoltaics has progressed merely from 25 percent to 25.6 percent during the past 15 years -- meaning the industry is keen to explore alternatives.


Rongrong Cheacharoen/Stanford University

1 cm2 monolithic perovskite-silicon tandem solar cell.

A collaboration between the Massachusetts Institute of Technology (MIT) and Stanford University may be poised to shake things up in the solar energy world. By exploring ways to create solar cells using low-cost manufacturing methods, the team has developed a novel prototype device that combines perovskite with traditional silicon solar cells into a two-terminal "tandem" device.

As the team reports in the journal Applied Physics Letters, from AIP Publishing, their new tandem cells have the potential to achieve significantly higher energy conversion efficiencies than standard single-junction silicon solar cells.

Perovskite is an inexpensive crystalline material that can easily be produced in labs and, as it turns out, stacking it atop a conventional silicon solar cell forms a tandem that has the potential to improve the cell’s overall efficiency, a measure of the amount of sunlight the cell can convert into electricity.

The team focused on tandem solar cells because there was big room for improvement in their cost and market penetration. Tandem solar cells have only garnered a worldwide market share of 0.25 percent compared to silicon solar cells’ 90 percent. “Despite having higher efficiency, tandems are traditionally made using expensive processes -- making it difficult for them to compete economically,” said Colin Bailie, a Ph.D. student at Stanford and an author on the new paper.

Designing low-cost perovskite-silicon tandem solar cells

The team’s tandem approach focuses on keeping costs low and “integrates perovskite solar cells monolithically -- building them sequentially in layers -- onto a silicon solar cell, without significant optical or electrical losses, by using commonly available semiconductor materials and deposition methods,” explained Jonathan P. Mailoa, a graduate student in MIT’s Photovoltaic Research Laboratory and another co-author on the paper.

Before creating the tandems, the researchers first needed to design an interlayer to facilitate electronic charge carrier recombination without significant energy losses. “Fortunately, the physical concepts already exist for other types of multijunction solar cells, so we simply needed to find the best interlayer material combination for the perovskite-silicon pair,” Mailoa said.

To form a connecting layer, known technically as the semiconductor “tunnel junction,” between the two sub-cells, the team used degenerately doped p-type and n-type silicon, which facilitates the recombination of positive charge carriers (holes) from the silicon solar cell and negative charge carriers (electrons) from the perovskite solar cell.

Because the two silicon layers are highly doped, “the energy barrier between them is thin enough so that electrons and holes in the semiconductor easily pass through using quantum mechanical tunneling,” Mailoa added.

While electrons from a perovskite solar cell won’t normally enter this tunnel junction layer, a titanium-dioxide (TiO2) layer commonly used in perovskite solar cells works as an electron-selective contact for silicon. This allows electrons to flow from the perovskite solar cell through the TiO2 layer, eventually passing into the silicon tunnel junction, where they recombine with the holes from the silicon solar cell.

How do perovskite-silicon tandem solar cells work?

Once the tandem is set up, it relies on its multiple absorber layers to absorb different portions of the solar spectrum. “The perovskite absorbs all of the visible photons [higher in energy], for example, while the silicon absorbs the infrared photons [lower in energy],” Bailie said.

Splitting the solar spectrum allows these specialized absorbing layers to convert their range of the spectrum into electrical power much more efficiently than a single absorber can convert the entire solar spectrum on its own.

“This minimizes an undesirable process in solar cells called "thermalization," in which the energy of an absorbed photon is released as heat until it reaches the energy of the absorber’s bandgap,” Bailie explained. “Using a high-bandgap absorber on top of the low-bandgap absorber recovers some of this energy in the high-energy photons that would otherwise be ‘thermalized’ if absorbed in the low-bandgap absorber.”

Another key part of the tandem’s design is that it uses a serial connection, which means that the two solar cells are connected in a manner so that the same amount of current passes through each of the solar cells. In other words, the same amount of light is absorbed in each solar cell and their voltage is added together.

Efficiency evolution ahead

The team’s tandem “demonstrated an open-circuit voltage of 1.65 V, which is essentially the sum of top and bottom cells, with very little voltage loss,” said Tonio Buonassisi, an associate professor of mechanical engineering at MIT who led the research.

An open-circuit voltage of 1.65 V was the highest best-case scenario the team had predicted, which indicates that their tunnel junction performs very well.

But an efficiency evolution is on the horizon. The efficiency record for single-junction perovskite cells ranges from 16 to 20 percent, depending on the formula used. “By contrast, the perovskite in our tandem is based on a technology that achieves only 13 percent in our lab as a single-junction device,” said Bailie. “Improving the quality of our perovskite layer will lead to better tandem devices.”

Another area for improving the tandem’s efficiency is by “reducing parasitic optical losses in other layers of the multijunction solar cell devices and predicting their efficiency potentials through simulation to determine whether or not this approach is truly cost effective,” added Mailoa.

The team also plans “to make improvements to the silicon bottom cell,” said Buonassisi. “The back contact isn’t well passivated, so we lose power at longer wavelengths. But the photovoltaic industry has developed several solutions for this problem…we just need to incorporate one best practice into our next-generation devices.”

While their work is still far from becoming commercially available, it frees other researchers to start to focus their efforts on important aspects of the multijunction device to help further improve both its stability and efficiencies in the future.

“This is the first step in the evolution of a technology that has the potential to disrupt the photovoltaic industry,” noted Bailie.

The article, "A 2-terminal perovskite/silicon multijunction solar cell enabled by a silicon tunnel junction," is authored by Jonathan P. Mailoa, Colin D. Bailie, Eric C. Johlin, Eric T. Hoke, Austin J. Akey, William H. Nguyen, Michael D. McGehee and Tonio Buonassisi. It will be published in the journal Applied Physics Letters on March 24, 2015 (DOI: 10.1063/1.4914179). After that date, it can be accessed at: http://scitation.aip.org/content/aip/journal/apl/106/12/10.1063/1.4914179

The authors of this paper are affiliated with the Massachusetts Institute of Technology and Stanford University.

This work was supported by the U.S. Department of Energy (DOE) under Contract No. DE-EE0006707, and by the Bay Area Photovoltaic Consortium (BAPVC) under Contract No. DE-EE0004946.

ABOUT THE JOURNAL

Applied Physics Letters features concise, rapid reports on significant new findings in applied physics. The journal covers new experimental and theoretical research on applications of physics phenomena related to all branches of science, engineering, and modern technology. See: http://apl.aip.org

Contact Information
Jason Socrates Bardi
American Institute of Physics
jbardi@aip.org
240-535-4954
@jasonbardi

Jason Socrates Bardi | newswise

More articles from Physics and Astronomy:

nachricht Measured for the first time: Direction of light waves changed by quantum effect
24.05.2017 | Vienna University of Technology

nachricht Physicists discover mechanism behind granular capillary effect
24.05.2017 | University of Cologne

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: A quantum walk of photons

Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.

The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....

Im Focus: Turmoil in sluggish electrons’ existence

An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.

We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...

Im Focus: Wafer-thin Magnetic Materials Developed for Future Quantum Technologies

Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.

Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...

Im Focus: World's thinnest hologram paves path to new 3-D world

Nano-hologram paves way for integration of 3-D holography into everyday electronics

An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...

Im Focus: Using graphene to create quantum bits

In the race to produce a quantum computer, a number of projects are seeking a way to create quantum bits -- or qubits -- that are stable, meaning they are not much affected by changes in their environment. This normally needs highly nonlinear non-dissipative elements capable of functioning at very low temperatures.

In pursuit of this goal, researchers at EPFL's Laboratory of Photonics and Quantum Measurements LPQM (STI/SB), have investigated a nonlinear graphene-based...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Marine Conservation: IASS Contributes to UN Ocean Conference in New York on 5-9 June

24.05.2017 | Event News

AWK Aachen Machine Tool Colloquium 2017: Internet of Production for Agile Enterprises

23.05.2017 | Event News

Dortmund MST Conference presents Individualized Healthcare Solutions with micro and nanotechnology

22.05.2017 | Event News

 
Latest News

Physicists discover mechanism behind granular capillary effect

24.05.2017 | Physics and Astronomy

Measured for the first time: Direction of light waves changed by quantum effect

24.05.2017 | Physics and Astronomy

Marine Conservation: IASS Contributes to UN Ocean Conference in New York on 5-9 June

24.05.2017 | Event News

VideoLinks
B2B-VideoLinks
More VideoLinks >>>