Cross-Linked Perylene Diimide-Based n-Type Interfacial Layer for Inverted Organic Photovoltaic Devices

This contribution describes the synthesis and characterization of a perylene diimide (PDI)-based n-type semiconductor and its application to organic photovoltaic (OPV) devices having inverted architecture. Films of N,N'-bis(3-trimethoxysilylpropyl)-1,6,7,12-tetrachloroperylene-3,4,9,10-tetracarboxyldiimide (Cl(4)PSi(2)) and blends of this material with various polymers are solution-deposited on tin-doped indium oxide (ITO) substrates as interfacial layers (IFLs). The organic IFL described in this work is based on the air- and light-stable PDI core, annealed at low temperatures compatible with flexible substrates, and crosslinks in air for compatibility with device fabrication. Morphological, optical, and electrochemical analysis of these IFL films demonstrate predominantly smooth surfaces and HOMO and LUMO energies of ~4.5 and 7.0 eV, respectively, which are ideal for accepting electrons and blocking holes in inverted devices. A cationic silane species is added to the Cl(4)PSi(2) at an optimum ~2-5 wt % to reduce IFL series resistance and enhance device performance. Also, a short light soaking procedure is necessary for completed devices to achieve high fill factors in current density-voltage analysis, a phenomenon previously only observed for inverted devices having an n-type inorganic IFL.