Researchers at the University of Sheffield have used silver (Ag) particles to form a SnO2:Ag nanoparticle composite transport layer, to improve the efficiency of perovskite solar cells.
SnO2 is known as one of the most efficient transport layers for perovskite solar cells. Adding the Ag nanoparticles increased the recombination rate (detrimental for device performance), and the charge carrier transfer and extraction was also enhanced (beneficial for device performance). In order to balance these opposing factors, the nanoparticle concentration was optimized at an intermediate concentration with a corresponding power conversion efficiency increase from 13.4 ± 0.7 % for reference solar cells without nanoparticles to 14.3 ± 0.3 % for those with nanoparticles.
The team stated that these devices are one of the first examples of, and exhibit the highest reported efficiency for, perovskite solar cells fabricated completely in air with nanocomposite oxide layers. The protocol developed and reported in the recent study to improve the nanocomposite transport layer has general applicability in other fields, including LEDs, FETs, and electronic devices where transparency and conductivity are also required.
The scientists used in their work an approach that is commonly adopted for the development of organic and dye-sensitized PV cells, for which scientists create composite transport layers with metal nanoparticles. In these devices, the nanoparticles act as a sort of antennae that trap the light in their proximity and contribute to exciting electrons into the conduction band in a more efficient way.
The team tested their approach in a perovskite solar cell constructed with an indium tin oxide (ITO) substrate, an ETL based on SnO2, a perovskite absorber, a hole transport layer (HTL) made of poly-triarylamine (PTAA), and an Ag metal contact, with all the cell layers being deposited in an air process.
The research team deposited Ag nanoparticles with thicknesses of 110 nm on the ETL via chemical synthesis and explained that an alternative process could be depositing thermally evaporated Ag nanoparticles between the ITO substrate and the SnO2 layer. It found, however, that only the first process can increase cell efficiency.
