Two-faced solar cells hit 80% efficiency with transparent electrodes

The conventional solar cells that you see on rooftops capture sunlight from only one side, but have you heard about bifacial solar cells? These innovative cells can generate electricity from sunlight falling on both their front and back sides, making them more efficient at harnessing solar energy.  

They are still not widely used, though. This is because bifacial solar cells require transparent electrodes to conduct electricity while allowing light to pass through. 

Making such electrodes has been challenging as scientists have struggled to find a transparent electrode material that is durable, stable, efficient, and affordable. Finally, a team of researchers from the Indian Institute of Technology (IIT) Dharwad has overcome this challenge. 

Their latest study highlights the development of a transparent electrode made of two layers of nickel oxide (NiO) and one layer of silver (Ag). This incredible advancement can not only make solar cells more efficient but also increase their adoption in industrial and agricultural setups where traditional solar cells can’t be used. 

For example, bifacial cells could be integrated into greenhouses and transparent windows of houses and large buildings.

Making triple-layer transparent electrodes

To construct this electrode, the IIT team employed a technique called low-energy physical vapor deposition. In this process, materials are vaporized in a vacuum chamber and then condensed onto a surface, forming thin, uniform layers. 

Using this method they formed a three-layer Nio/Ag/Nio (NAN) structure, resulting in an electrode less than 40 nanometers thick. This thin design makes it suitable for use in building materials and combining with other types of solar cells.

When they added this NAN electrode to their solar cells, the cells achieved power conversion efficiencies of 9.05% and 6.54% when light was shined on different sides. 

The cells also had a high bifaciality factor of 72%, meaning they could effectively capture light from both directions. Moreover, when the cells were tested for over 1,000 hours without any protective covering, they performed with an impressive 80 percent efficiency.

“Even after 1000 h in ambient circumstances, the BPvSC (bifacial perovskite solar cell) device retained more than 80% of its initial PCE without any encapsulation. The performance of the device begins to decline after 2 weeks, which is typical with PvSCs,” the study authors note.

A highly practical solar innovation

This isn’t the first transparent electrode design for bifacial solar cells. However, previously proposed approaches used materials such as indium tin oxide (ITO) that are expensive and fragile. 

Moreover, these materials require special treatment to become durable and flexible. NAN, on the other side, has no such requirements and is comparatively cheaper. Therefore, it has the potential to make bifacial solar cell technology more accessible and affordable. 

“The work presented here can provide a design strategy for TEs that can be included in PvSC for use in tandem devices, agrivoltaics, and automotive technologies, among other potential uses,” the study authors said

“This breakthrough highlights the immense potential of bifacial perovskite solar cells in advancing solar energy technology,” Dhriti Sundar Ghosh, senior study author and a professor at IIT Dharwad, added.

The study is published in the Journal of Photonics for Energy