Conventional structure : PEDOT:PSS is used as a hole transport layer which is hygroscopic and acidic in nature leads to device degradation and low work function metal Al is used as a cathode which is sensitive to oxidation. These reasons are responsible for instability.

Inverted structure: Mostly used metal oxide (ZnO) as a ETL and relatively High work function Metal Ag is used as a Anode.

Its all about the architecture you plan to design. Inverted OSCs can give you more options of using the electron transport layer and helps to get rid of the Al difusion problem to the active layer. However, the problems associated with PEDT:PSS are still there.

Thank you Omar A. Abdulrazzaq and Nafees Ahmad for your valuable comments.