Dear Mohammad,

Hope you are well,

When a material contains crysatllograohic defects which forms electronically active recombination centers, then one has to passivate them to render them

inactive meaning they no longer act as recombination centers.

These active bond sometimes called dangling bonds. There passivation is accomplished by saturating them by the suitable passivating gas such as hydrogen and oxygen.

One of the famous material which is used in photovoltaic is the amorous Silicon which is passivated by hydrogenation. Surfaces are also oxidized to passivate them. It took long time to reduce the active defects on the interface between silicon and silicon dioxide to produce the MOSFET transistors.

Best wishes

Dear professor Zekry

thanks for your complete and vivid answer.

That's just the matter.

Dear Muhammad

yeah that's the right poin of view too.

thanks.

Dear Mohammad

I trust you are well and safe.

Adding to the previous explicit explanations, halide Perovskite photovoltaics in particular have several interfaces, including the HTL/perovskite and ETL/perovskite interfaces. Because of surface defects, these interfaces are also highly defective, accumulating more defects than even grain boundaries.

The high defect density at the interfaces leads to high nonradiative trap-assited recombination losses, resulting in loss in Voc and PCE.

Passivating these interfaces by introducing suitable thin layer interface modifiers between the HTL and perovkites for instance, improves the Voc and PCE.

Some modifiers used in the past include PTAA, PH3T, Al2O3, graphene oxide, PCBM, fullerene derivatives and more.

Apart from passivating the interface and surfaces , these modifiers also passivate grain boundaries, prevent moisture ingress and ensure suitable band alignment.