FTO serves as a transparent to prevent contacts from leaking to charge carrier layers, it should have good conductivity, high transmission and good adhesion to the layers; it however offers some sheet resistance to the PCE of the solar cell. That's why you get increased performance when you remove it.

Dear Milimo,

Did you have any article Milimo AMOS Nalianya to talk about this case?

Can you please kindly help me share the article?

Thank you very much!

@Vinh Pham, checkout this publication

:Fluorine doped tin oxide as an alternative of indium tin oxide for bottom electrode of semi-transparent organic photovoltaic devices

AIP Advances 9, 085220 (2019); https://doi.org/10.1063/1.5104333

Thank you very much Milimo AMOS Nalianya !

Dear Vinh,

thank you for posting this interesting technical question. As organometallic chemists we are no experts in perovskite chemistry. However, I made the experience that it often pays off to directly check out the "Publications" and "Questions" sections of RG. For example, please have a look at the answers given to the following closely related questions which have been asked earlier on RG:

Why most of the people used FTO instead of ITO for perovskite solar cell fabrication?

https://www.researchgate.net/post/Why-most-of-the-people-used-FTO-instead-of-ITO-for-perovskite-solar-cell-fabrication

and

Can anyone please inform me the roles of different layers used in Perovskite Solar Cell? I want to know the details mechanism. ???

https://www.researchgate.net/post/Can-anyone-please-inform-me-the-roles-of-different-layers-used-in-Perovskite-Solar-Cell-I-want-to-know-the-details-mechanism

Good luck with your work and best wishes!