The perovskite layer does not need to cover the entire surface, but reveals holes, and scientists have demonstrated that it creates a protective layer against short circuits.
Metal-organic perovskite layers for solar cells are usually fabricated on a compact substrate using a spin-on technique that usually has many holes but achieves an astonishing level of efficiency.These holes do not cause front-to-back contact The obvious short circuit between the HZB team led by Dr. Marcus Baer now uncovers the reason Marcus Baer has worked with the team led by Professor Henry Snaith of BESSY II (Oxford University).
The conversion efficiency of early metal-organic perovskites was only a few percent (compared with 2.2% in 2006), however, the progress was rapid and the record level now is well above 22%.
The efficiency of the current commercialized silicon solar cell technology has been continuously increasing for more than 50 years. Films made from low cost metal-organic perovskites can be large by spin-coating and subsequent baking (whereby the solvent evaporates and the material crystallizes) The scale of production will make the technology more attractive.
Perovskite film in the hole
Nonetheless, the thin perovskite films spin-coated on compact substrates are often not perfect, but show many pores, and samples of the seminal perovskite group led by Prof. Henry Snipes also showed these holes The problem is that these holes can cause adjacent layers of the solar cell to come into contact, resulting in a short circuit in the solar cell, which will greatly reduce the efficiency level, which was previously not observed.
Establish a thin layer
Now, samples of Henry Snaith were carefully examined by Marcus Bar and his group and the Spectro-Microscopy group at the Fritz Haber Institute, which mapped the surface morphology by scanning electron microscopy, and then analyzed the area of the holes using the BESSY II spectroscopic method We can show that even in the holes the substrate is not really exposed, and apparently where the deposition and crystallization process can prevent short circuits, PhD student Claudia Hartman explains.
Prevent short circuit
At the same time, scientists were able to determine that the energy barriers that charge carriers must overcome can be recombined with each other directly in contact with the contact layer.Transmission materials for electron transport layer (TiO2) and positive charge carrier (Spiro MeOTAD) are not actually direct In addition, the composite barrier between the contact layers is sufficiently high that these cause solar cell internal losses to be extremely small despite the many pores in the perovskite film.