Substituent position engineering of phosphine oxide functionalized triazine-based cathode interfacial materials for flexible organic and perovskite solar cells

Abstract

Abstract The grand challenge involved in inverted organic solar cell (IOSC) and perovskite solar cell (PSC) technology is to control the interfacial losses at the interface of the photoactive layer with the electron extracting electrode. Herein, three organic small molecules, namely o-(F)-PO-TAZ, m-(F)-PO-TAZ and p-(F)-PO-TAZ, consisting of phosphine oxide (P O) functionalized 1,3,5-triazine (TAZ) with a fluorine atom ( F) at the ortho (o)/meta (m)/para (p) positions of the phenoxy group attached to the TAZ unit are developed via a rational design approach and used as cathode interfacial layers (CILs) in flexible IOSCs and PSCs. We realized that the F position particularly affects the glass transition temperature (Tg) of the PO-TAZ derivatives, which in turn exerts a positive effect by maintaining robust and smooth morphological features. This gives the IOSC and PSC devices an F position-dependent performance. Particularly, ZnO/p-(F)-PO-TAZ-based flexible IOSC and PSC devices display not only high power conversion efficiencies (PCEs) of 7.68% and 14.64% but also long-term stability that are superior to those of the control and o-(F)- and m-(F)-PO-TAZ-based solar cell devices. The current work offers new findings on constructing photoactive (organic or perovskite) layer/CIL interfaces and assists in the rational design of CILs to facilitate efficient photovoltaic devices.