New shiny kids in the Solar Block, perovskite solar cells are organo-metallic halide that promises to be one of the most widely used materials in the solar sector.

Here, we take a closer look at perovskite structure, its basic formula, and the current ongoing research.

What is Perovskite?

Selected as one of the biggest scientific breakthroughs of 2013 by the journal editors of Science and Nature, Perovskite is a type of crystal structure found in a select bunch of materials. It  is named after the natural mineral Calcium Titanium oxide (CaTiO₃), with a general chemical formula ABX₃.

Perovskites are synthesized in the lab by mixing two expensive salts – lead halides, and organic halides. The solution forms an ink. This can be applied in an ultrafine, uniform layer by layer via inkjet printing or spin coating method.

  Perovskite crystals hve a cubic arrangement of atoms, where ‘A’ is usually a larger positively charged ion, surrounded by a cage of ‘X’ negatively charged ions, and ‘B’ is the cation residing at the center of the cube. Such an arrangement of atoms results in a three-dimensional framework exhibiting various properties depending on the elements and compounds involved.

Due to their unique characteristics, perovskite materials have received special attention in the field of photovoltaics. Since these materials can be synthesized using various elements in different combinations, the properties can be tailored as per application, including harvesting solar energy.

Check this vid on perovskite crystal structure: 

 

What is a Perovskite Solar Cell exactly?

A perovskite solar cell is a kind of solar cell with perovskite crystal structures to convert sunlight into electric current.

Halide perovskites gained little to no attention until layered organometal halide perovskites were reported to exhibit a transition from semiconductor to metal with increasing dimensionality. Besides the change in electrical properties, the band gap decreased with an increase in dimensionality from 2D to 3D. A narrow band gap is ideal for solar cell applications.

  The power conversion efficiency of 3.1% when X is Br, and 3.8% when X is I. When the TiO₂ film has a thickness of about 3.6 um, CH₃NH₃PbI₃ perovskite showed an absorption coefficient 10 times greater than that of the conventional ruthenium-based molecular dye.

 

  Research in Perovskite Solar Cells

As per   the U.S. Department of Energy Solar Energy Technologies Office (SETO), 4 main challenges must be tackled for the technology to become commercially viable. Every challenge represents a unique set of barriers and needs specific technical and commercial goals to be met. 

• Stability and Durability:

Perovskite solar cells have proved to have excellent power conversion efficiency with a potential for high performance. However, their limited stability in comparison to other PV technologies limits their commercialization. Perovskites can decompose when they undergo a reaction with moisture and oxygen, or when exposed for excessive periods to light, heat, or applied voltage.

  Improvement in cell durability is crucial for commercial production of perovskite solar cells.

  To reach the solar market, the cells need to perform optimally for at least two decades, irrespective of the other benefits offered by it. Early perovskite cells degraded within minutes or hours. Intense research has improved the operation time to several months.

To improve the stability of the material, researchers focus their efforts on decreasing the reactivity of the perovskite surface by formulating the structure with alternative materials. Alternative surrounding device layers and electrical contacts, advanced encapsulation materials, and approaches to mitigate the degradation sources during fabrication and operation are considered.

Another problem with the assessment of degradation in perovskites is the lack of consistent testing and validation methods. Since test conditions like encapsulation approaches, atmospheric conditions, illumination, electrical bias, and other parameters can provide valuable data, it is important to assess these parameters. Because there is a lack of standardization of these variables, it becomes more challenging to compare the results and predict the performance on the field based on test results.

• Power Conversion Efficiency

The perovskite PV cells have proven their outstanding power conversion efficiency in small-area devices. However, these devices have not displayed stability or feasibility to fabricate at a large scale. For the widespread development of perovskites, the cells need to have good stability while performing efficiently in large-area modules. 

Perovskites can be tuned to respond to different colors in the spectrum of sunlight by simply changing the composition of the material. Also, a variety of formulations have exhibited high performance. This flexibility permits the perovskites to be combined with another, absorber material that is differently tuned. Such a combination can be used to deliver more power from the same device. This is termed tandem device architecture.

The ability of the perovskites to be tuned to absorb different wavelengths of the solar spectrum is an advantage over silicon PV materials.

• Manufacturability

A perovskite solar cell is a thin-film device that is built with layers of materials that can be either printed or coated from liquid inks or vacuum-deposited. To produce uniform, high-performance perovskite material in a large-scale manufacturing environment is quite challenging, also there is a substantial difference in small-area cell efficiency and large-scale module efficiency.

There are two major production types for perovskite solar cells:

• Sheet-to-Sheet: The device layers are deposited on a rigid base. This base acts like the front surface of the completed solar module. Such an approach is commonly used in the Cadmium telluride thin-film industry.
• Roll-to-Roll: The device layers are deposited on a flexible base, which can be either used as an interior or exterior portion of the complete module.

 

With proven technology and immense future potential, perovskite solar cells are certainly somthing to keep an eye on in the renewable energy material industry.