A Simple Cathode Interfacial Material Performs Well in Organic Solar Cells

A low‐cost perylene‐diimide diphosphonium bromide cathode interlayer material ((1,3,8,10‐tetraoxo‐1,3,8,10‐tetrahydroanthra[2,1,9‐def:6,5,10‐d'e’f']diisoquinoline‐2, 9‐diyl)bis(4,1‐phenylene))bis(triphenylphosphonium)bromide (named as CIL‐4), whose photovoltaic performance is comparable with recognized poly[(9,9‐bis(3′‐(( N,N ‐dimethyl)‐ N ‐ethylammonium)‐propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluor ene)] (PFN‐Br) is reported in this article. Unlike PFN‐Br, CIL‐4 is easy to prepare and well soluble in highly polarized solvents such as H 2 O, CH 3 OH, and DMF. An impressive power conversion efficiency (PCE) of 15.08% is demonstrated. In addition, CIL‐4 is very cost‐effective because of the one‐step synthesis and purification method. CIL‐4 also favorably tends to form a high‐quality amorphous films by a simple solution process. The femtosecond transient absorption (TA) experiment verified electron transfer occurs between n‐type electron acceptor Y6 and the CIL‐4 film interface. This work indicates that perylene‐diimide diphosphonium bromide can be a competent cathode‐adjusting material in the optoelectronic field.