Enhancing Perovskite Solar Cell Efficiency with Tandem Design

Perovskite solar cells (PSCs) have emerged as a game changer in the renewables industry over the years. They have proven to be more affordable than traditional solar panels and can be effectively installed in the front facades and rooftops of buildings. Another feature of perovskite solar cells that has impressed environmental scientists is that it does not emit toxic lead as in the case of traditional solar panels. In addition to that, many research companies have entered the solar space with different ways to produce PSCs on a large-scale basis. This has also resulted in the emergence of PSCs produced through different processes such as tandem technology, Inkjet printing, radiative annealing process, etc. which in turn has enabled these PSCs to be produced for commercial purposes.

Research companies across the globe have employed nanotechnology and nano materials to enhance the efficiency of Perovskite solar cells. At present, these PSCs provide up to 30% efficiency. With the help of nanotextures, the researchers have managed to design solar cells with lower reflection losses and improved open-circuit voltage. Other methods that have proved effective in enhancing the power conversion efficiency of the PSCs include additive engineering, defect passivation, interface engineering and transmission material optimization.

Increasing Perovskite Solar Cell Efficiency through Tandem Design

Adding Spectral Splitters:

One of the most sought-after methods in improving the efficiency of the Perovskite solar cells is by using a spectral splitter between the top and bottom of the two-terminal PSC tandem solar cells. This method is particularly useful for solar cells that use large top cell band gaps such as solar cell-water splitting architectures that require large open-circuit voltages.

The spectral splitters have an estimated efficiency of 45%(theoretical) in comparison to the other PSCs found in the market.Researchers achieve this by reflecting the light back to the top cell, creating an extra path for absorption. This effectively reduces the loss of light from the front cell. By improving the light absorption, the solar cells can provide higher throughput compared to the traditional panels, thereby becoming more energy efficient.

The spectral splitters are of two types, the one that reflects light back to the top cell like a mirror is called planar splitter while the other that reflects light in an angular fashion is called a lambertian splitter. Researchers have found that both these splitters are useful when it comes to enhancing the PCE of the solar cells.

Conversion Materials:

Most solar cells suffer from lower efficiency due to loss of energy from the thermalization of charge carriers which occurs at the time of absorption of high energy photons. By using conversion materials, the researchers enhance the capability of PSCs to utilize a wider spectrum of solar energy through the absorption of Infrared light. This process results in the release of visible light that the cells effectively absorb and convert into electricity for commercial use.

The conversion can be up or down depending on the energy of the photons. During the up-conversion process, researchers convert photons of low energy into photons with high energy. This enables the solar cells to effectively close the spectrum band gap. On the other hand, the down-conversion process converts a photon with high energy to low energy photon with minimal thermalization loss. Another advantage of using conversion materials is that it does not affect the electrical properties of the solar cells and goes on to perform its functions in an independent manner.

An important difference when it comes to the conversion materials is their location. Researchers place the up-conversion materials between the PV material and back reflector, while they place the down-conversion materials on top of the PV material. The conversion materials are usually lanthanides and transition metals that have unique optical, magnetic, and catalytic properties.

Mechanically Stacked Configuration:

Another solution in improving the PCE of the Perovskite Solar cells is by using mechanically stacked tandem design. The mechanically stacked design is more compatible with higher efficiencies and helps in extracting power from lower and top modules of the cells in a separate manner.

The advantage of this method is that researchers utilize different solar cells stacked upon each other, generating greater efficiency and a high degree of flexibility. Moreover, the mechanical stacking provides electrical isolation to the sub cells which helps in independent collection of carriers to the external circuit.

Optical Concentrators:

The Perovskite Solar Cells perform best when brought under direct sunlight. Though there are devices that track the movement of the sun throughout the day, such devices are expensive and unviable for large scale installations. However, researchers can better harness and concentrate sunlight in an efficient manner using optical concentrators, regardless of the angle and frequency of the light.

Researchers have developed the Axially Graded Index Lens, also known as Agile, as an optical concentrator prototype to improve the efficiency of PSCs in a simple and elegant manner. The device is built in the shape of an inverted pyramid, effectively capturing around 90% of the sunlight. The inverted pyramid shape allows the light to enter the lens from any angle and channel it onto the cells.

Final Thoughts:

Researchers can produce PSCs in several ways using different cell architectures, such as P-type, N-type silicon, and busbar configuration. However, as far as efficiency is concerned, tandem design seems to have an edge over the other cell architectures. With more research happening in the development of solar cells, new architectures with much higher efficiencies are likely to emerge.

In addition to utilizing cell architectures, spectrum splitters, or optical concentrators for higher PCEs, achieving better results with perovskite solar cells also relies on proper installation and careful maintenance of the panels.

Certain practices such as installing the solar panels in shady areas or in angles that deflect the sunlight can also result in poor efficiency of the solar cells, irrespective of the cell architecture used. Additionally, the surface of solar panels should be cleaned periodically to ensure better light absorption.

With the emerging clean and renewable energy trend, developments over enhancing the output performance of the PSCs will be a top priority in the days ahead.