The most common types of solar panels are manufactured with crystalline silicon (c-Si) or thin-film solar cell technologies, but these are not the only available options, there is another interesting set of materials with great potential for solar applications, called perovskites. Perovskite solar cells are the main option competing to replace c-Si solar cells as the most efficient and cheap material for solar panels in the future.
Perovskites have the potential of producing thinner and lighter solar panels, operating at room temperature. In this article, we will do an in-depth analysis of this promising technology being researched by the solar industry. Here we will explain the basics of perovskite solar cells, compare them to other technologies, and explain different variations of solar cells featuring perovskite.
What are perovskites and perovskite solar cells?
Perovskites, unlike crystalline silicon, comprise a family of materials receiving the name after the mineral they are made of, which in turn is named after Lev Perovski. Perovskites were researched as absorber materials for the first time in 2006, with published results in 2009.
The perovskites have a great potential in the solar industry for the creation of perovskite solar cells, making them the most promising of the 3rd generation photovoltaics. In just 5 years the efficiency of the perovskite solar cell has increased from less than 4% to above 20%, a little more than 15 years later, the efficiency increased even further, achieving a perovskite solar cell efficiency of 30%.
Perovskites have a closely similar crystal structure to the mineral composed of calcium titanium oxide, the first discovered perovskite, but researchers are exploring many perovskite options like the methyl ammonium lead triiodide (CH3NH3). This mineral can be modified to adopt custom physical, optical, and electrical characteristics, making it more suitable for different types of applications.
The perovskite solar cell applications are quite diverse, thanks to this technology featuring unique characteristics like a high-adsorption coefficient, long carrier separation transport, a larger distance between electrons and holes, and the capacity to be tuned to absorb different light colors (wavelengths) from the solar spectrum.
As a result of featuring these characteristics, perovskite solar cells have the potential to replace traditional c-Si solar panels and even most thin-film photovoltaics.
To have a better understanding of this technology, it is important to analyze it in depth. In this section, we will dive into the details of perovskite solar cell, explain their structure and materials, how it works, and the major setbacks that slow the mass production of perovskite solar panels.
Structure and materials for the perovskite solar cell
The structure of perovskite solar cells differs slightly from the classical structure of Al-BSF c-Si solar cells. Perovskite solar cells can be manufactured using conventional n-i-p or p-i-n architecture, sandwiching the perovskite absorber layer between a Hole Transporting Layer (HTL) and an Electron Transporting Layer (ETL). The order of these layers varies with the architecture of the cell.
There are two types of perovskite absorber layers: planar and mesoporous. Planar layers remove the mesoporous scaffold material, leaving only the perovskite layer. Mesoporous perovskite layers, on the other hand, place the liquid perovskite solution over scaffold materials, with the materials for the mesoporous scaffold layer being conductors like titanium dioxide (TiO2) and Zinc Oxide (ZnO), or insulators like Aluminum Oxide (Al2O3) and Zirconium dioxide (ZrO2).
Perovskite solar cell manufacturers place a perovskite absorber layer between ETL and HTL, with both of these layers being sandwiched between electrodes, and the transparent layer is then covered with glass. The most widely used method uses deposition with a One-Step Method, but there are different manufacturing methods using Two-Step depositions, Vapor-Assistance, or Thermal Vapor Deposition.
Depending on the usage of a mesoporous or planar perovskite layer and the architecture of the solar cell, different materials can be placed for the anode/cathode of the layer and different orders for the back sheet and the transparent layer. An n-i-p perovskite solar cell features a Gold (Au) anode and a Fluorine Doped Tin Oxide (FTO) transparent layer, while p-i-n perovskite solar cells can feature Aluminum (Al) cathodes and Indium Tin Oxide (ITO) anodes.
How does the perovskite solar cell work?
On a simple basis, perovskite solar power is generated similarly to most photovoltaic technologies, under the photovoltaic effect. The photons in the solar light hit the perovskite absorber layer, exciting and freeing electrons, creating an electron-hole (e-h) pair. The electron then moves towards the HTL, which transports the electron to the conductor, powering the load.
After electrons powered the load by flowing as an electric current, they get collected by the ETL in the perovskite solar panel, this layer also suppresses the backflow of holes. Excited electrons might fill holes instead of flowing through the load as electricity, accounting for some of the perovskite solar power losses in a process called surface recombination.
The road for mass-production of perovskite solar panels
Perovskite is a fairly new and growing solar cell technology with its first reported application in 2009, a little more than a decade ago. Crystalline silicon was first discovered in 1916, with its first solar application dating back to 1950, more than 70 years ago. This makes it understandable that the mass production of perovskite solar cells might still encounter some barriers along the way.
For perovskite solar panel technology to be commercially successful, experts and perovskite solar cell manufacturers have to work on solving several challenges of this technology, focusing specifically on producing efficient mass-manufacturing processes, perovskite solar cells with larger sizes, and increasing the lifespan of the cell.
There are still many challenges the solar industry has to overcome for perovskite to be a viable technology for real long-term applications. The good news is that researchers all over the world are putting their best efforts into solving these problems for the future.
Perovskite vs. Crystalline silicon solar cells
Crystalline silicon technology has been the norm for many decades in the solar industry. This is a matured technology with well-established mass production processes focused on cost-reduction for c-Si PV modules. This technology features an Al-BSF structure, using monocrystalline c-Si (Mono c-Si) or polycrystalline c-Si (Poly c-Si) for the absorber layer.
Considering the promising future for perovskite solar panels, it is important to compare this technology against the currently well-established crystalline silicon solar panels. In the following table, we compare both technologies, to provide you with a deeper understanding of the potential of this new growing trend in the solar industry.
|Monocrystalline Silicon (mono c-Si)||Polycrystalline Silicon (poly c-Si)||Perovskites|
|Highest Recorded Efficiency||25.4%||24.4%||29.15%|
|Lifespan||25-30 years||30 months (2.5 years)|
|Light Absorption Potential||Wavelengths of light of 1,100 nm||Wavelengths of light of 850 nm|
|Applications||Residential & Industrial||Residential & Industrial||Potential for residential, commercial, industrial, Building Integrated Photovoltaics (BIPV), tactical, and space applications.|
The perovskite solar cell efficiency is an excelling aspect where this technology stands out. Researchers have achieved up to date a recorded efficiency of 29.15%, almost 30%, which is 3.75% more than the highest efficiency recorded for crystalline silicon Al-BSF technology. Considering that c-Si is a highly matured technology, this shows the promising potential for perovskite solar panels.
However, one of the major setbacks that perovskite solar cell technology faces is the lifespan of the cells. The c-Si solar cell technology is a matured technology achieving lifespans of up to 30 years, while perovskite solar panels barely last 30 months in the best of cases, currently making it impractical for most real-world applications.
An interesting difference between c-Si and perovskites is the light absorption potential. Crystalline silicon is limited to absorbing wavelengths equal to or superior to 1,100 nm, while perovskites can be tuned to respond to a wider variety of colors in the solar spectrum. This feature can be exploited in the future, creating solar panels that convert most wavelengths in the solar spectrum. Perovskite solar cells also have the potential to be used for space applications.
The manufacturing cost for perovskite solar cells is currently parallel to the lowest cost for crystalline silicon. This makes it an interesting option, especially considering that c-Si is a matured technology with years of development in the cost-reduction area. It is estimated that perovskite solar panels in the future could cost around $0.10 per watt, making it one of the cheapest PV technologies in history.
Finally, the different applications for perovskites solar panels could end up rapidly replacing c-Si technology, after well establishing the mass-production manufacturing process and figuring out the way to extend the expected lifetime to market levels.
Perovskite vs. Other thin-film solar cell technologies
Perovskite solar cell technology is considered a thin-film photovoltaic technology, since rigid or flexible perovskite solar cells are manufactured with absorber layers of 0.2- 0.4 μm, resulting in even thinner layers than classical thin-film solar cells featuring layers of 0.5-1 μm. Comparing both technologies provides an interesting contrast between them.
Except for III-V GaAs thin-film technology featuring the highest recorded efficiency at 68.9%, perovskite solar cell efficiency at 29.15% could be considered the most efficient thin-film technology, surpassing the 14.0%, 22.1%, and 23.4% conversion efficiency for amorphous silicon (a-Si), cadmium telluride (CdTe), and copper indium gallium selenide (CIGS) thin-film technologies, respectively.
Perovskite solar cell technology also far surpasses every other thin-film option in its cost. Regular thin-film photovoltaics cost around $0.40 to $0.69 per watt, while GaAs technology has a cost of $50 per watt. All of these prices far surpass the low $0.16 per watt cost for perovskite solar cell technology, which can be brought down even further to $0.10 in the future.
Thin-film solar technology is known for its great performance at different temperatures due to low-temperature coefficients, but perovskite solar cell technology performs even better than most thin-film photovoltaics (CdTe, CIGS, and a-Si) that feature temperature coefficients ranging from -0.172%/ºC to -0.36%/ºC. GaAs solar cell is the only technology with a temperature coefficient of 0.09%/ºC, surpassing the performance of perovskite solar cells.
CdTe and CIGS PVs are mainly limited to commercial and industrial applications, while a-Si thin-film is used for BIPV, and GaAs solar cells are used for space applications. Flexible perovskite solar cell technology has the potential to be used in different applications, replacing thin-film photovoltaics, and it can also be used in residential applications since it features an outstanding efficiency and low cost.
Bonus: What are perovskite-silicon tandem solar cells?
When learning about perovskite solar cells, is important to consider a variation of perovskite, which is the perovskite-silicon tandem solar cells. These are solar cells featuring a unique design that combines traditional crystal silicon with perovskite solar cells.
Perovskite silicon tandem solar cells are created by stacking a perovskite absorber layer (including HTL and ETL), on top of an n-type c-Si layer, featuring a recombination layer between them, made out of hydrogenated a-Si (a-Si:H) or nanocrystalline silicon (nc-Si). These solar cells work by taking advantage of c-Si harnessing long-wavelengths and perovskite harnessing short-wavelengths to generate electricity.
Perovskite silicon tandem solar cells partially stabilize perovskite material by featuring a wide bandgap and maintaining the efficient charge carrier transport of the original perovskites. These solar cells deliver interesting benefits like a recorded efficiency of 29%, fewer required manufacturing steps and contact layers, a larger voltage output, and a great performance in high temperatures.
Just like with single-junction perovskite solar cells, perovskite silicon tandem solar cells face several setbacks like a reduced lifetime for the cell due to the effect of halide segregation and other factors. Researchers are still figuring out how to extend the lifespan of these cells. They have already figured out ways to produce 20-year lifespan cells, but with relatively rapid degradation for the generation capacity.
Another important technology that should not go unmentioned is perovskite-perovskite tandem solar cells. These cells feature a similar structure to perovskite silicon tandem solar cells but use different layers of perovskite. Perovskite-perovskite tandem solar cells require fewer fabrication processes, and less energy to recycle the cells, but most importantly, a fast Return of Investment (ROI) of just 4-4.5 months.
Key Takeaways: Benefits of perovskite solar cells
Perovskite solar cell technology is highly promising and delivers excellent benefits for the solar industry and customers, but like with most technologies in its maturing process, it requires researchers to find ways to overcome limiting factors like the stability of the cell, lifespan, mass-manufacturing protocols, and several other aspects that still limit perovskite solar cell applications.
The future of perovskite solar cell technology is bright and will most likely carry the solar industry to new horizons in the following decades. This technology has already achieved amazing benefits in just a little more than 15 years, like the following ones:
- Efficiency is close to 30% for a single solar cell.
- Excellent performance in extreme weather with a temperature coefficient of -0.13%/ºC.
- Low manufacturing costs.
- Potential for many applications.
- Thinner and lighter solar cells than most thin-film photovoltaics.
Perovskite Technology Outlook
While currently there are a few setbacks, researchers are investigating ways to produce stable perovskite solar cells, to make them work like any other solar cell. With the potential of delivering faster ROIs in less than a year, and producing high amounts of electric power, there are many projections for perovskite solar technology.
Some studies do not only consider single-junction perovskite solar cells but are also considering combining perovskite in perovskite-perovskite, perovskite-CIGS, and perovskite-Organic Photovoltaic (OPV) tandem. These combinations could yield excellent benefits like higher efficiency, increased stability, and several other benefits.
One future potential for perovskite solar cells is a higher increase in their efficiency. While this technology has already achieved a 29.15% efficiency, the future could produce an efficiency close to 38%, which is its theoretical maximum perovskite solar cell efficiency.
The potential for a wide range of perovskite solar cell applications is another aspect in which this technology excels. As a result of perovskite having a more flexible and lighter design than most thin-film photovoltaics, and higher efficiency than traditional rigid c-Si solar panels, this technology has the potential to completely replace both thin-film and silicon-based models, becoming the main technology in the solar industry for residential, commercial, utility-scale, tactical, and even space applications.